UiV.Vli ILLIKOi AT UR< ' 7 JHRCULA^^ AGRICULTURELJBRARY Experiments in ERADICATING FIELD BINDWEED By L. V. SHERWOOD and R. F. FUELLEMAN AGRICULTURE LIBRARY SEP 2 6 1990 UNIVERSITY OF ILL!NO!3 Bulletin 525 UNIVERSITY OF ILLINOIS AGRICULTURAL EXPERIMENT STATION : *' . ' CONTENTS PAGE INTRODUCTION 473 History and Spread . . . -. .-,. . ; 474 Identification and Description 474 GROWTH HABITS . . . . , . . , . 477 Seed Production. . . . . 480 Rooting Habits ....'.' 483 ERADICATION BY CUiTURAL METHODS 487 Bare-Fallowing '.-..- 487 Clean Cultivation 491 ..,-. j . Small Grains and Fallowing .495 SMOTHERING AND BURNING 495 DESTROYING WITH CHEMICALS 496 2,4-D 496 Chlorates 500 . Other Chemicals 503 FINAL CHECK-UP NECESSARY .504 SUMMARY. . ... . V.A,:. ..:-. .- ,. . 505 - . * -- Urbana, Illinois January, 1948 Publicafions in the Bulletin series report the results of investigations made or sponsored by the Experiment Station EXPERIMENTS IN ERADICATING FIELD BINDWEED By L. V. SHERWOOD and R. F. FuELLEMAN 1 . INTRODUCTION AIONG THE WEEDS that grow in Illinois, one of the farm- er's worst enemies is field bindweed (Convolvulus arvenfis] L.). Townspeople, too, have cause to be concerned over the control of this weed, for it chokes out the grass from their lawns and the vegetables from their gardens. The damage that field bindweed does to agricultural crops-- is severe. Maintaining that "crop production on heavily infested land is rarely profitable," loan companies often refuse mortgages on farms known to be infested with this weed. Figures from experiments in Kansas 2 show how field bindweed reduces crop yieTds: Sorghum, fer example, which yielded 3.92 tons of silage per acre on clean, land, yielded only 2.06 tons on bindweed-infested soil. Yields of Sudan grass hay decreased from 2.2 tons on clean land to 1.54 tons on" in 1 -, fested soil. There was also a reduction in barley from 21 ,5 tjp 7.5 bushels; in wheat from 20.9 to 13.7 bushels; and in oats from. 30.9 to 16.6 bushels per acre. In Illinois more concentrated effort and research have gone into the control of field bindweed than of any other wee-d in the history. of the state. Yet every year many old infestations grow larger, while new infestations appear where none existed before. No farm is free" from danger as long as there is an infestation anywhere near. Because of the difficulty in eradicating this plant, many farmers have given up trying to control it. Other farmers, however, have been successful. Both they and research workers have proved that field bindweed can be controlled in America, as well as in Europe, its place of origin. 1 L. V. SHERWOOD, formerly Assistant Chief in Crop Production ; and R. F. FUELLEMAN, Associate Professor of Crop Production Research. 2 ZAHNLEY, ]. W., and PICKETT, W. F. Field bindweed and methods of control. Kans. Agr. Exp. Sta. Bui. 269. 1934. ..' ' 473 474 BULLETIN No. 525 [January, History and Spread A native of Europe, field bindweed was first introduced into the United States along the Atlantic seaboard. As early as 1739 it was mentioned in Virginia. 1 It was reported in Pennsylvania in 1812, Mas- sachusetts in 1814, Maine in 1824, Kansas in 1877, Wisconsin in 1882, Ohio in 1885, Nebraska in 1888, and Iowa in 1889. By now it has spread into every state of the Union. 2 Field bindweed probably came into Illinois about 1890 or earlier. It was introduced in garden and crop seeds and in feeds. Tho now undoubtedly in every county, it is more common in the northern than in the southern part of the state. Most of the infestations are relatively small and scattered. Often, however, an infestation may remain small and comparatively inactive for 10 to 20 years; then it will suddenly begin to spread rapidly, causing severe losses unless controlled. It is expected that the plant will gradually become better adapted to Illinois soil and climate and that, when this occurs, damage will be more wide- spread and severe. Identification and Description Field bindweed is known by a variety of names, including "creeping Jennie," "European bindweed," "small-flowered morning glory," and The blossoms of field bindweed vary from white to light pink. In shape they resemble those of a morning glory but they are usually much smaller, being about 1 or 11/2 inches in di- ameter. (Fig. 1) "creeping Charlie." A perennial plant, it starts blossoming in June in Illinois, grows profusely in July, and continues less vigorously until late fall. 1 KIESSELBACH, T. A., PETERSEN, N. F., and BURR, W. W. Bindweeds and their control. Nebr. Agr. Exp. Sta. Bui. 287. 1934. 2 Minn. Dept. Agr., Dairy and Food. Bui. 17. 1934. 1948] ERADICATING FIELD BINDWEED Upper specimens are hedge bindweed, Convolvulus sepium ; the lower ones are field bindweed. These two weeds are quite similar in appearance, but field bindweed can be identified by the small bracts on the flower or seed stems (lower left). The bracts on hedge bindweed are larger and situated at the base of the flower. (Fig. 2) 476 BULLETIN No. 525 [January, The underground root system of field bindweed is extensive, growing as deep as the water table, which in Illinois is often 8 to 10 feet below the sur- face of the soil. The vertical ruler is 18 inches long. (Fig- 3) The blossoms are white to light pink, about 1 to li/i inches in diameter, resembling those of a small morning glory (Fig. 1). Tho the leaves may vary in size and shape, they are usually narrow, lance- shaped, pointed, and lobed (Fig. 2). People often confuse field bindweed with other viny plants. The best way to identify it is to look for the two small bracts between the flower and the main stem (Fig. 2). No other viny plant common in the state has bracts which appear on the flower stem in exactly the same way. 1948] ERADICATING FIELD BINDWEED 477 The root system is deep and connected underground (Fig. 3). As the roots grow horizontally, they send up new shoots at irregular intervals. The plant also propagates by seeds. GROWTH HABITS Field bindweed produces seeds (Fig. 4) from July to September in Illinois. The mature seeds normally lie on or in the soil until the following spring before germinating. Seed germination begins in May Seeds of field bindweed may live for a long time in the soil before germinat- ing. Those shown on the left are natural size; those on the right have been magnified about 3i/ 2 times. (Fig- 4) and continues thruout the summer. During the first 6 weeks of growth, the roots of field bindweed seedlings grow rapidly downward (Fig. 5) until they reach a depth of about 4 feet. Then lateral branching of the roots begins and, soon after, new plants shoot up in a radius of 3 or 4 feet around the original plant (Fig. 6). During the first season an individual plant will spread until it covers an area 3 to 5 feet in diameter. It may produce a few blossoms late that season. Field bindweed is one of the last plants to be killed by frost. In central Illinois growth is renewed about April 15 each spring. Spring growth, however, is usually very slow until warm weather. The period of most rapid vegetative growth at Urbana is usually during the last part of May or early June. Blossoming begins immediately after this period, usually during the first half of June (Fig. 7). 478 BULLETIN No. 525 [January, Field bindweed grows rapidly. The plant on the left is 20 days old; that on the right, 35 days old. Both were photographed July 5. To control this plant efficiently it is necessary to recognize and eradicate it early. See also Figs. 13 and 14 as aids to early identification. (Fig. 5) The blossoming period is long, ending about August 1 (Fig. 7), except for a few scattered blossoms which appear until frost. Con- sequently it is important to guard against seed production thruout the entire growing season. After the blossoming period, or normally by August 1, field bindweed goes into semi-dormancy for about a month. During this period very little vegetative growth occurs and many of the basal leaves die. Established plants renew growth about Sep- tember 1 and continue growing until freezing weather. 1948] ERADICATING FIELD BINDWEED 479 All this growth developed from one seedling in 160 days (May 28 to No- vember 3, 1939) at Urbana. The roots were over 6 feet deep. (Fig. 6) 1200 5 10 15 20 25 30 5 10 15 20 25 30 4 Variation in blossom production of field bindweed during three summer months at Urbana. (Fig. 7) 480 BULLETIN No. 525 [January, Seed Production Originally it was believed that field bindweed produced few if any seeds in Illinois. More recently it has become evident that seed produc- tion in Illinois is heavy (Fig. 8). The quantity of seeds produced, however, may vary considerably with different infestations and in different years (Table 1). Both plant habits and the effects of weather help to explain these variations. Table 1. Flower and Seed Production of Field Bindweed: Urbana, Illinois, 1937-1941 Year Blossoms per square yard Seeds per square yard Blossoms setting seed 1937 number 77 number 1 percent 1.3 1938 341 7 (early summer) 1.6 1939 2 277 - 686 14 1940 1 737 1 400 38 1941 1 007 349 16 Field bindweed appears to be a cross-pollinated plant. During four years of repeated experiments with controlled self-pollination at Urbana, no seeds were produced by individual bindweed plants which had been covered with cheesecloth. When cross-pollination was per- mitted, varying amounts of seed were produced (Table 2). Results indicate that flowers are more likely to be fertilized by pollen from another plant than by pollen from the same plant. This conclusion is supported by cytological studies made thruout Illinois (Table 3). It was found that plants produced an abundance of viable pollen even in areas where no seed developed. Table 2. Effect of Controlled Pollination on Seed Production of Field Bindweed: Urbana, Illinois, 1940 Increase in seeds Treatment Blossoms Blossoms setting seed Seeds per capsule Seeds set per original blossom set per original blossom, due to controlled pollination number perct. number number perct. Normal pollination permitted . . . 6 080 38 2.1 .80 Flowers cross-pollinated by hand and left open*. . . 141 50 2.9 1.42 77.5 Flowers emasculated after open- ing; not cross-pollinated by hand, but left open 203 25 2.5 .61 Flowers emasculated after open- ing; cross-pollinated by hand and left open* .."... 135 39 2.6 1.03 68.9 a Controlled pollination (cross-pollination by hand) was done by placing the pollen in an atomize r and spraying it onto the exposed stigmas of another plant. The blossoms were left open because pre- vious tests had shown that protective devices always caused the blossoms to die. 1948] ERADICATING FIELD BINDWEED 481 482 BULLETIN No. 525 [January, Table 3. Pollen Viability of Field Bindweed Gathered From Various Locations in Illinois in 1939 Location of infestation Date of collec- tion Total grains counted Number of grains aborted* Number of grains viable Percent of grains viable Seed produc- tion Urbana A June 29, 30, 32294 3556 28738 89.0 Very light July 7 Urbana B July 8 17250 2 118 15 132 87.7 None Sibley July 11 12693 2856 9837 77.5 Light Rochelle July 11 13388 6453 6935 51.8 None Viola July 12 22835 3833 19002 83.2 Very heavy Urbana C Aug. 20, 129176 57054 72122 55.8 Light Sept. 9 Total 227636 75870 151766 66.7 1 In the shriveled aborted grains the cytoplasmic content was only partly developed and the germinal furrows were completely closed. In sectioned material the nuclei in these shriveled grains appeared to be disintegrating. Judging from the above experiments, isolated infestations where the plants developed vegetatively from one parent plant will produce very little if any seed, but seed production will increase as unrelated infestations become more prevalent. This may in part account for the lack of seed production in some areas and the abundant production in other places. It may also partially explain the sudden changes which occur from one year to the next in the amount of seed produced in a given infestation or area. Variations in weather probably account for many of the changes in seed production from year to year. Weather may affect the opening and closing of the blossoms, the number of insects which carry the pollen, and perhaps the viability of the pollen. Pollen of field bindweed is normally shed about 8:00 a.m. and prob- ably remains viable as long as the blossoms are open. On a clear morning blossoms usually open about sunrise and remain open until noon. This gives ample opportunity for cross-pollination to take place. During dry weather, therefore, plants growing close to unrelated strains are likely to produce considerable seed. If rain falls during most of the day when pollination would nor- mally occur, the number of seeds set is low. Morning rainfall interferes with seed production more than rain in the afternoon. On rainy morn- ings blossoms open later than in dry weather sometimes not at all. If they open later, there is less time for insects to carry pollen and this in turn results in fewer seeds. Seed production, therefore, is not likely to be so great in years of heavy rainfall as in dry years. In all years, however, particularly where unrelated infestations grow close together, seed production is a very serious problem in Illinois. Sometimes the seeds become scattered in the soil and then the problem is even more difficult. These seeds are slow to lose their 1948] ERADICATING FIELD BINDWEED 483 viability and may lie in the soil for as long as six years 1 before germi- nation. When this happens, the time needed for eradication is greatly prolonged. Rooting Habits Field bindweed roots penetrate the soil to a depth of 7 to 10 feet in Illinois (Fig. 3). In established infestations the roots may spread This growth occurred in one year's time from a single root fragment. The fragment was planted July 8, 1937; the growth was photographed June 23, 1938. The ruler is 18 inches long. (Fig. 9) laterally as much as 10 to 15 feet in one growing season. As they grow horizontally they send up new shoots. It is also possible that pieces of root, cut off during cultivation, may help to spread the weed to other parts of the field (Fig. 9). Trials 1 KIESSELBACH, T. A., PETERSEN, N. F., and BURR, W. W. Bindweeds and their centrol. Nebr. Agr. Exp. Sta. Bui. 287. 1934. 484 BULLETIN No. 525 [January, $ tf I 3 I U) m to M T3 I O jj I s .0 area agme taken K3i 32 3* fs .S jj "'S d, *.!, TTT si E" or= * -v J2- ou^ Isl 111 & I o Ej ^ 5 CD o O g M^^ [z >>>>>. ^s^e^s c c c ^i . i i fefek o'-o'-o'- OOO COTCicfifloi OOO CQ, 5 Q' 3 Q. i -, [fl C 1948} ERADICATING FIELD BINDWEED 485 have been made at Urbana (Tables 4, 5, and 6) to determine under which conditions root fragments are most likely to grow. All frag- ments tested were severed at the time of gathering. Growth of the fragments varied greatly with the amount of food stored in the roots. In the 1936-1939 tests fragments from areas which had been previously unmolested sent up the greatest amount of growth (Table 4). Pieces of root from land that had been fallowed sent up practically no growth. The effect of food reserves in the roots was shown in 1940 tests also (Table 5). Fragments from areas where bindweed tops had been kept removed all season sent up no shoots, while 64 percent of the fragments from unmolested areas grew. Fragments taken from the top foot of soil in areas which had been previously disturbed, either by fallowing or by normal cultivations, were less likely to grow than fragments from greater depths (Table 6). In 1937 only 6.7 percent of the fragments from the first foot of soil grew, whereas the percentages from the second and third foot layers Table 5. Effects of Watering, Root Reserves, Size, and Kind of Tissue on Growth of Field Bindweed Root Fragments: Urbana, Illinois, 1940 Date of planting* Kind of tissue Length of fragments planted Moisture at time of planting 1 " S ; th^tTew Effect of watering at time of planting Sept 5 Root Root Root Root inches 6 6 Watered Watered Unmolested Unmolested 36 64 50 36 100 68 Sept. 6 .... Average for watered fragments . . Sept. 5 6 6 Unwatered Unwatered Unmolested Unmolested Sept. 6 . .... Average for unwatered fragments Effect of root reserves Sept. 6 Root Root 6 6 Watered Watered Unmolested Kept clear of tops all season 64 Sept. 6 .... Effect of size of fragments Sept. 5 Root 6 Watered Unmolested 36 Sept. 5 Root 3 Watered Unmolested 4 Effect of kind of tissue Sept. 6 Root 6 Watered Unmolested 64 Sept. 6 Stem 6 Watered Unmolested Twenty-five fragments were used for each of the ten plantings. All fragments were taken from upper foot of soil and planted about 3 inches deep. b Rainfall on September 9, 1940, was .48 inch. 486 BULLETIN No. 525 {January, Table 6. Growth of Field Bindweed Root Fragments of Varying Lengths and Depths of Planting and Taken From Different Layers of Soil: Urbana, Illinois, 1937 (Fragments taken from soil which had previously been fallowed or normally cultivated) Layer of soil from which roots were taken Depth of planting Results when roots of different length were used for planting 1 in. 2 in. 3 in. 4 in. Sin. 6 in. First foot inches 4 Grew deep did nc Grew Grew >t grow) Grew Grew Grew Grew Second foot 2 (Fragments planted 2, 6, 9, and 12 inches .... Grew Grew Grew Third foot 4 6 9 12 2 .... Grew .... .... Grew 4 6 9 12 ..... .... Grew Grew Grew Grew Grew Grew Grew Five fragments of each length were gathered from each foot of soil. Each of the five fragments was planted at a different depth. Altogether 90 fragments were planted, each representing a different combination of layer of soil, length of fragment, and depth of planting. were 33.3 and 36.7 respectively. It is probable that the structure of renewed growth above the plowed depth is morphologically stem rather than root. That would help to explain why fragments from near the surface of plowed areas did not send up many shoots. In trials to determine the effect of moisture on the growth of root fragments, it was found that watering at the time of planting did not increase the growth of fragments. In fact, fragments which were not watered in trials at Urbana grew more than the watered fragments (Table 5). The amount of moisture in the soil from which the fragments were taken did, however, affect the growth of the fragments. Pieces planted on June 4, July 8, and August 21, 1937, were all taken from land where corn had grown the previous year. That some of the July 8 plantings grew while none of the June 4 or August 21 plantings did so (Table 4) may be attributed to the fact that there was greater mois- ture in the soil from which the July 8 plantings had been taken. These results indicate that in wet years there is greater danger of infestations spreading from root fragments than in dry years. Cultiva- tions are not so effective when the soil is wet as when the soil is dry, for root hairs are less likely to be damaged when the soil is wet. Frag- ments clinging to the plow are much more likely to grow when they are scattered in the field while the soil is wet. To be most effective, cultivations should be done on dry soil and 1948] ERADICATING FIELD BINDWEED 487 in such a way that severed roots are broken loose from the soil particles. Cultivations should also break the roots into as small frag- ments as possible. The smaller the fragments, the less likely they are to grow (Tables 4, 5, and 6). ERADICATION BY CULTURAL METHODS To get rid of field bindweed, both the extensive root systems of established plants and the seeds which are already in the soil must be destroyed. In Illinois the roots can be eradicated in one and a half to two growing seasons by cultural methods, the time and expense varying according to the way the work is done. Seeds are more of a problem. If they have been plowed under, it may take several years to get rid of them entirely. If, however, they are brought to or left near the surface of the soil, most of them can be cleared out within a year. Alternate freezing and thawing, the presence of enough oxygen for germination, the action of certain molds, and various other conditions will break the dormant stage of seeds which are close to the surface and will cause germination. The re- sulting seedlings can then be destroyed. It is, of course, much cheaper to prevent seed production than to destroy seeds after they are in the soil. If an eradication program cannot be started at once, the plants should be plowed or otherwise molested each time they start blooming. This will prevent seed pro- duction for the time being. One or two well-timed shallow plowings or cultivations in a season may be enough for this purpose. The culti- vations will also sever some of the roots and make it less likely that they will send up new plants. Bare-Fallowing Bare-fallowing for one and a half to two growing seasons will kill field bindweed roots. The root system cannot live indefinitely with no leaves, for without leaves no food can be manufactured. Each time the top growth is destroyed some of the food stored in the roots is utilized in sending up new shoots. If the process is repeated enough times, the food supply in the roots will be exhausted and they will eventually die. The cultivations will also destroy seedlings and keep seeds from getting into the soil. Cultivations should be started early in the season. When culti- vations were started in May (Table 7) the weeds were destroyed in two 488 BULLETIN No. 525 [January, Table 7. Effect of Frequency of Bare-Fallow Cultivations on Eradication of Field Bindweed: Urbana, Illinois, 1938-1939 (Cultivations begun in May) Days after plants came up before they were culti- vated again" Percent of ground origi- nally covered with field bindweed Date of cultivations Number of cultivations required for eradication of roots Started 1938 Ended 1939 1938 1939 Total 0... percl. ..'... 90 May 25 May 25 May 25 May 25 May 25 May 25 May 25 May 25 July 7 Aug. 21>> July 28 Aug. 12 Aug. 31 Oct. 2 Oct. 16 Not eradi- cated 29 15 11 11 9 8 7 9 9 6 6 6 6 6 38 24 17 17 15 14 13 6 90 10 90 12 85 14 80 16 80 20.. . . 85 28 . . . 95 Field cultivator equipped with duckfoot shovels was run at a depth of 4 to 5 inches. b Bindweed was not eradicated as quickly as it might have been, because the roots in the cul- tivated area were being fed thru underground root connections with surrounding unmolested plants. c This frequency resulted in five cultivations each year, which were not enough to eradicate the weed. seasons or less. Delaying the first cultivation until August 23 (Table 8) lengthened the time required for eradication. Some of the plants in this test were not killed even by the end of the fourth season. Cultivating- should preferably be done about 10 days after the plants emerge, or about every 2 weeks (Tables 7 and 8). Even tho cultivations made at 20-day intervals have been satisfactory (Table 7) it is safer to plan on the 2- week interval. This will allow leeway for any unexpected delays caused by the weather. More frequent cultiva- tions simply add to the expense. Furthermore, if cultivations are too frequent, it may take longer to kill the plants, perhaps because they tend to become dormant rather than die. Depth of cultivation does not greatly affect the time needed for complete eradication (Table 9), except when cultivations are very Table 8. Effect of Frequency of Bare-Fallow Cultivations on Eradication of Field Bindweed: Urbana, Illinois, 1938-1941 (Cultivations begun in August) Days after plants I came up before they were cul- tivated again* Date of cultivations ( Completeness of root eradication Number of cultivations Started 1938 Ended 1940 1938 1939 1940 1941 Total 0... Aug. 23 Aug. 23 Aug. 23 Aug. 23 Aug. 23 Oct. 11 Oct. 21 Oct. 11 Not eradi- cated Not eradi- cated Complete Complete Complete Incomplete Incomplete 10 6 5 4 3 25 15 10 8 8 15 10 7 7 5 5 5 50 31 22 24 21 5 10 15 20 Duckfoot cultivator was run at depth of 4 to 5 inches. 1948] ERADICATING FIELD BINDWEED 489 Table 9. Effect of Depth and Frequency of Bare- Fallow Cultivations on Eradication of Field Bindweed: Urbana, Illinois, 1937-1938 Depth of cultiva Number of cultivations Average interval between cultiva- tions (days)" Seasons required to completely eradicate roots (approximate) 1937 1938 Total 20 20 6 7 5 5 4 4 3 2 40 19 17 13 9 8 8 5 4 6 10 13 15 23 25 27 49 43 1J 1 1J| 1H i IH iji 1 8 iM 3 inches 13 6 inches 10 8 4 4 . . . 4 30 inches 2 2 Each plot was cultivated as soon as top growth appeared; usually no more than two leaves showed above the ground. Other experiments at the Illinois Station have shown that it is better to allow a limited amount of top growth before cultivation (Table 7). shallow less than 3 inches. If only the surface is scraped, some plants will be missed entirely, and more time and much more frequent working will be required for complete eradication. Since too-shallow cultivations must be repeated so often, they in- crease the cost of eradication. On the other hand, if the cultivations are too deep, the expense is also prohibitive. Considering economy and effectiveness, the best depth is probably 3 to 4 inches just enough to assure that the cultivator will work properly. Overlapping blades, such as sweep or duck foot types (Fig. 10), are most effective in destroying field bindweed. They are less likely to miss A field cultivator with sweep-type, overlapping blades such as these is the most satisfactory implement for destroying field bindweed. Fewer plants are missed with this type of blade. (Fig. 10) 490 BULLETIN No. 525 [January, Even thoro disking did not sever all the top growth of the bindweed in this plot. A sweep-type cultivator would have done a better job. (Fig- 11) The short, low-yielding corn in foreground is growing on land bare-fallowed the preceding year. To get normal growth of corn in Illinois after such treat- ment, phosphate applications are necessary. (Fig. 12) 1948] ERADICATING FIELD BINDWEED 491 plants than the ordinary disk. Many plants have been found still grow- ing the next day after a disk has been used (Fig. 11). After bare- fallowing it is sometimes advisable to grow an inter- tilled crop for one or more seasons to get rid of any seeds which may have lodged deep in the soil before the eradication program was begun. In the past farmers have hesitated to grow corn after bare- fallowing because of the reduced yields (Fig. 12). Recent studies have indicated, however, that addition of phosphate to the soil will counteract the de- pressing effects of bare-fallowing. The phosphorus should preferably be in the superphosphate form. One application of 250 pounds of 20-percent superphosphate per acre was found to keep the corn crop up to normal. Since soil types vary, however, tests should be made to determine the most effective application for a particular soil type. Small grains will grow satisfactorily on land that has been bare- fallowed the preceding year. Clean Cultivation For a number of reasons, clean cultivation of an intertilled crop like corn is preferable to the bare- fallow method of controlling field bindweed. That clean cultivation is as effective as bare-fallowing was shown by tests made at Sibley, Illinois (Table 10). An advantage of clean cultivation is that this method does not have the depressing effects on subsequent crop yields that bare- fallowing has. Moreover, the crop grown may not only repay the cost of eradication but may also return a profit, as shown by the trials at Sibley and Urbana (Tables 11 and 12). It is more profitable to use this method with corn than with soybeans. The principal disadvantage of row-crop tillage is that bindweeds missed by the cultivator have to be hoed out by hand. If clean cultivation is to rid an area of bindweed, it must do two things: It must destroy all top growth often enough thruout each season that the plants are never more than 5 or 6 inches tall; and it must keep seeds from forming. As in bare- fallowing, cultivations should be about 2 weeks apart. The usual seedbed preparation will ordinarily keep down field bindweed until the corn has emerged, if implements are used that will cut off all the top growth of bindweed. One or two extra cultivations during this period may be necessary. When the growing corn is cultivated, all top growth of bindweeds missed by the machine should be hoed out by hand after each cultiva- tion. Work on the experimental plots at Urbana and Sibley showed 492 BULLETIN No. 525 [January, Table 10. Effectiveness and Costs of Different Crop Sequences in the Eradication of Field Bindweed: Sibley, Illinois, 1940-1941 Sequence of crops Operations needed for eradication (in addition to usual farm practices) Total hours of man labor" Total hours for 2-plow tractor and duckfoot cultivator Cost of treat- ment 11 Complete- ness of root eradica- tion 1940, corn 8 hoeings, one every 2 weeks from June 28 to Oct. 11 28 1941 , corn 8 hoeings, one every 2 weeks from June 23 to Oct. 1 . . 14 Total for 2 years 42 1940, corn 8 hoeings, one every 2 weeks from June 28 to Oct. 11 28 1941, oats Plowed Aug. 1 . 2 5 bare-fallow cultivations from Aug. 8 to Oct. 3 . . 5 Total for 2 years. . . 35J 1940, oats Plowed July 18 2J 4 bare-fallow cultivations from Aug. 21 to Sept. 30 4 1941, soybeans 8 hoeings, one every 2 weeks from June 23 to Oct. 1 . . 60 Total for 2 years 66^ 1940, soybeans 8 hoeings, one every 2 weeks from June 28 to Oct. 11 56 1941, corn 8 hoeings, one every 2 weeks from June 23 to Oct. 1 . . 14 Total for 2 years 70 4.20 $12.60 $ 8.40 2.63 5.25 #16.28 $ 2.63 4.20 18.00 $24.83 16.80 4.20 321.00 Complete Not quite complete Not quite complete Complete a Time is the actual amount used on small plots at Sibley. For bare-fallow operations the cost is probably higher on these small plots than under farm conditions. b Costs figured at 30 cents an hour for labor and 75 cents an hour for tractor. This should be adjusted according to local wages. Table 11. Net Profit per Acre Where Field Bindweed Was Eradicated While Crops Were Grown: Normal Crop Rotation Plots at Sibley, Illinois, 1940-1941 Sequence of crops Gross income from crops" Normal cost of producing crops b Extra cost for eradicating bindweed Net profit on land while bind- weed was eradicated $42 $20 $ 8.40 (28 hr.) $13.60 .... 42 20 4.20 (14 hr.) 17.80 Total for 2 years $84 $40 $12.60 (42 hr.) $31.40 $42 . 50 $20 $16.80 (56 hr.) $ 5.70 Second year, corn 42 20 4.20 (14 hr.) 17.80 $84 . 50 $40 $21.00 (70 hr.) $23.50 a Gross income from crops was based on a 60-bushel yield of corn worth 70 cents a bushel and a 25-bushel yield of soybeans worth $1.70 a bushel. b This is the average cost on moderately productive farms. It includes all costs of growing and harvesting the crops, taxes, and interest on the land. c Cost of hoeing was figured at 30 cents an hour, a minimum rate at the time. Cost will vary with locality. that this is practicable. After the corn is laid by, hand-hoeing should be continued at 10-day to 2-week intervals. As in bare- fallowing, the most satisfactory implement for the clean- cultivation method is a sweep- type cultivator with overlapping blades. 1948] ERADICATING FIELD BINDWEED 493 The best depth is that at which the cultivator operates best usually about 3 to 4 inches. Old, established plants, with their deep perennial root systems, take about li/2 years to eradicate. Then, if the infestation is in a seed-producing area, two or three more seasons may be needed to de- Table 12. Comparative Costs per Acre for Eradicating Field Bindweed by Different Methods: Urbana, Illinois, 1940-1941 (Based on 1940 prices) Costs and income Corn (no bind- weed) Clean Chlorates cultivation Bare-fallowed n 2?jflS in corn (8 days after S .l" r i ?> ,? H mfe ~ che <~> p y e e r a sa^To d d second year) First year Weed control $. . . $ 8.40 8.08 10.89 27.37 29.68 2.31 4.20 8.08 10.89 23.17 29.68 6.51 8.82 12.60 3 6.00* to $11. 00 8.08 14. 08* to 19.08 -14.08* to -19.08 3.00* to 6. 00 8.08 11.08* to' 14. 08 -11.08* to" -14. 08 -25.16* to -33.16 46.58* to 54. 58 $ 64.00 8.08 Taxes and interest on investment 8.08 10.89 18.97 29.68 10.71 72.08 -72.08 16.00 8.08 Second year Weed control Taxes and interest on investment 8.08 10.89 18.97 29.68 10.71 21.42 24.08 Net income -24.08 -96.16 117.58 Two years Total cost of weed eradication, includ- NOTE: Prices of labor, operation of equipment, yields, corn, etc., are based upon a report of an hour for man, tractor, and duckfoot field cultivator. Chlorates cost 10 cents a pound at the time of the experiment. Sometimes a complete kill is obtained by as little as 3 pounds of chlorates per square rod. More often 5 or 6 pounds are required per square rod. Data for other years will, of course, depend on price of labor, yield and price of corn, etc. * These figures, based on data from plots at Sibley, Illinois, are included for comparison. Table 13. Summary of Experiment on Maximum Age at Which Seedlings May Be Killed by One Shallow Cultivation: Urbana, Illinois, 1941 Percent of plants surviving one cultivation made varying number of Planting date weeks after seedlings came up 1 wk. 2 wk. 3 wk. 4 wk. 5 wk. 6 wk. 7 wk. 8 wk. 9 wk. May 25 022 2 7 June 24 .... 24 ? 19 1 20 S 20 8 41 ? 66.7 Aug. ll b 9 1 3.2 a Each planting of 30 scarified seeds was replicated 3 times. The number of plants produced for each week's test ranged from 10 to 24. b Because of cool weather, growth was slow and survival was poor from the August 11 planting. BULLETIN No. 525 [January, These field bindweed seedlings are one week old. At this stage, the roots are very shallow and the plants can usually be killed by one cultiva- tion. (Fig. 13) By the time seedling plants are four weeks old, they may be 9 inches long or longer, including top growth and roots. More than one cultivation may be needed to kill seedlings this old. (Fig. 14) 1948] ERADICATING FIELD BINDWEED 495 stroy seedling plants. During this period the object is to encourage the seeds to germinate and then to kill the young plants. Frequent shallow cultivation is the rule, plus whatever hoeing is necessary to destroy all the seedlings and any old plants that still persist. Cultivations at Sibley late in 1941 (Table 10) and also in 1942 and 1943 were made primarily to destroy seedlings. Seedlings not more than 2 weeks old can be killed by a single shallow cultivation, according to trials at Urbana (Table 13). Small Grains and Fallowing Bare-fallowing certain plots at Sibley, Illinois, after the small- grain harvest and until fall did not eradicate field bindweed. After three successive grain crops the plots had as much bindweed as before the eradication program was started if not more. Furthermore, this method did not prevent bindweed from producing seed. Of the small grains observed at Sibley, rye was most effective in retarding the growth of bindweed and preventing seed production. Winter wheat was next. Spring oats and barley did not compete well with the bindweed. Indications are therefore that spring grains are less effective than fall-seeded grains, mainly because they are slower in getting started in the spring. SMOTHERING AND BURNING Smothering Smother crops will not eradicate field bindweed. Alfalfa, soybeans, and other rank-growing crops, however, help to prevent the rapid spread of the weeds and they may, at times, discourage seed production. Covering field bindweed plants with such materials as roofing paper, straw, and manure will lower the rate of spread and may sometimes help prevent seed production, but it will not rid the land of this weed. Burning Burning an infested area was no more effective than if the weeds had been scraped off with a hoe. New growth appeared immediately. If, however, burnings are frequent enough so that there is never more than 5 or 6 inches of top growth, the weeds will eventually be de- stroyed. There may be occasions when one timely burning will destroy seeds already formed. Burning in the flowering stage will prevent seed production. 496 BULLETIN No. 525 [January, DESTROYING WITH CHEMICALS No chemicals have been found which, because of either economy or effectiveness, can completely take the place of cultural methods of control. Nevertheless, there are times when chemicals should supple- ment cultural methods and times when they will have to be used ex- clusively. They may have to be relied on entirely when the infestation cannot be reached with cultivation equipment or when it is too small to warrant the use of large-scale equipment. Sometimes, even under field conditions, it is actually cheaper to use chemicals than to cultivate. 2,4-D Sprays and dusts containing 2,4-D (2,4-dichlorophenoxyacetic acid) are excellent aids in the eradication of field bindweed. They are recom- mended where bindweed is growing in perennial grasses, in small grains, and in corn. They may be used either as a substitute for or in combination with cultivation. In small grains, spraying field bindweed with 2,4-D makes harvest- ing easier and also makes infested fields eligible for certification. Sprays containing 2,4-D may cause some damage to corn or small grains, under adverse conditions, but as long as the treatment results in a net gain, or prevents weed seed production, it is justified. Seed production prevented with 2,4-D. At Urbana one treatment of 2,4-D applied to field bindweed in the bud stage kept seeds from forming. However, there may be some advantage in making treatments slightly before bud stage, since there is often a delay in the effect of the chemicals following treatment. If treatment is not made until the bud stage, a delay in killing may result in the ripening of seeds after the chemicals are applied. Effect on roots. It was found at Urbana that one application of 2,4-D, made before the bindweed blossomed and while it was growing rapidly, destroyed the top growth and roots to a depth of 12 to 24 inches. It would appear, therefore, that repeated, properly timed treat- ments might eliminate the pest, acting in the same manner as repeated cultivations. However, considerable top growth must be allowed before each treatment so that the plants can absorb enough 2,4-D to be effec- tive on the already extensive roots. While the top growth is developing enough for chemical treatment, the roots are also re-establishing them- selves, both in extent and in food reserves. The result has often been that the second treatment has killed the roots no deeper than did the first application. This may account for failure to obtain conclusive re- sults in the eradication of field bindweed with 2,4-D. 1948] ERADICATING FIELD BINDWEED 497 Table 14. Effect of 2,4-D Chemicals on Field Bindweed: Urbana, Illinois, 1947 2,4-D material Pounds per acre Date of applica- tion Gallons of carrier per acre Days re- quired to kill top growth Number of shoots per square rod, Oct. 16, 1947 1 4 July 7 160 14 1.4 July 7 160 9 Butyl ester 1.4 July 7 160 9 1 Ammonium salt 1.4 July 7 160 12 1 Ammonium salt 2.8 July 7 160 10 Butyl ester. 2 8 July 7 160 8 Butyl ester . . .8 Oct. 16 2 2 Use of 2,4-D with cultural methods. Even tho field bindweed has not yet been completely eradicated by 2,4-D alone, the chemical may have a very practical place as a supplement to cultural methods of control. For example, the destruction of the roots to a depth of 12 to 24 inches would be a great help before starting fallow or clean- cultivation procedures. Furthermore, there are times when the soil is too wet to properly operate cultivation equipment. Applications with 2,4-D at this time would keep down the top growth until cultivations could be made. This chemical can also be used instead of the hoe method for preventing top growth and eliminating seedlings in certain crops after it is no longer possible to use cultivation implements in the crop. Chemical elimination of seedlings is particularly advantageous since they are destroyed without disturbing the soil. Thus, in contrast to cultural methods, seeds deep in the soil are not brought to the surface to sprout. While this method may not eliminate weed seeds from the soil as rapidly as repeated cultivations, it offers the possible advantage of better weed control with fewer operations. Furthermore, actual records show that where chemical control has been continuously prac- ticed over a period of years, certain weed species totally disappear. Use in grassy areas. Most hay and pasture grasses have been found to be resistant to 2,4-D. One advantage of the chemical, there- fore, is that in grassy areas it can be used to eliminate or control certain weeds, including field bindweed, without the destruction of grasses so important in the prevention of erosion. When to apply. In general, results are best when the plants are treated while in the active, growing stage of development, just before blossoming. The 2,4-D chemical is a little slow-acting in cool weather and may be almost totally ineffective in extremely hot, dry weather, but it can usually be applied with reasonable assurance of success in any growing weather regardless of temperature. 498 BULLETIN No. 525 [January, Concentration and amount. Directions on the containers give recommended concentrations for 2,4-D sprays. It is impossible to offer general recommendations for the use of commercial preparations since each often contains a different percentage of 2,4-D. In general, 1/2 to 1 pound of 2,4-D (free acid basis) per acre gives good control with a minimum of damage to associated crops. In noncrop fields and grass meadows heavier concentrations can be used to get quick results. For eradication, more than one application is usually necessary. In Illinois, 2,4-D is usually applied in water solution, altho in the South dusts of 2,4-D have been successfully applied by airplanes at rates as low as 1.2 pounds of 2,4-D free acid to the acre. In the past solutions containing .1 to .3 percent of 2,4-D free acid have been used in Illinois at rates of 100 to 300 gallons per acre. Present trends, how- ever, are toward low-gallonage applications of 1/2 to 1 pound of acid per acre. New data .from various experiment stations indicate that the amount of 2,4-D recommended for an acre should be mixed with just enough water or oil for adequate coverage. This will vary with the type of equipment available, and with the height and density of plants. Enough solution should be applied to completely moisten the unwanted vegetation, but there is no advantage in applying so much that it runs onto the ground. As little as 2 gallons of carrier have been used (Table 14), but 5, 10, and 15 gallons of liquid are easier to spread over an acre than 2 gallons. Precautions. 1. Blanket applications of 2,4-D should be made only in resistant crops. Spot treatments are sometimes used in suscep- tible crops but there is always a risk that these crops will be affected. While some crops are resistant to 2,4-D at all stages of growth, other crops are susceptible in all stages, and still others are resistant at certain stages and are susceptible at other times. Most seedlings of both crops and weeds are killed or seriously injured by 2,4-D. Anyone contemplating the use of 2,4-D in crops should determine whether the crops are resistant. Following is a list of the important susceptible, intermediate, and resistant crops. Susceptible. Too readily injured by selective spraying of weeds in them and readily injured by spray drift: Practically all garden flowers and vegetables. Nearly all cultivated legumes including alfalfa, red clover, white clover, alsike clover, sweet clover, field peas, soybeans, vetches, lespedezas, and others. Other susceptible groups are cotton, flax, hemp, sorghums, sugar beets, and Sudan grass. 1948] ERADICATING FIELD BINDWEED 499 Intermediate. Not so readily injured as Group 1. Selective spraying with suitable concentrations and formulations of 2,4-D is possible in many of these plants with caution as to stage of growth: Asparagus, barley, oats, wheat, rye, bentgrass, buffalo grass, corn, pota- toes, and strawberries. Resistant. Selective spraying with 2,4-D of weeds in these plants is generally possible: Evergreens, needle-leaved. (Pines, spruces, red cedar and other junipers, arbor vitae, hemlock, yews, etc. Some injury to new growth has been noted from spraying while in rapid growth.) Most hay and pasture grasses. Bromegrass, timothy, common ryegrass, orchard grass, Kentucky bluegrass, Canada bluegrass, and Bermuda grass. Also most weedy grasses like crabgrass, foxtails, goosegrass, and others. 1 2. In addition to the crops and ornamental plants included in the above list, practically all fruit trees and vines are susceptible. In general, therefore, avoid using 2,4-D in gardens, vineyards, and orchards. If the chemical is used in these areas, extreme care must be exercised. 3. Great caution is necessary in the use of 2,4-D near fields where susceptible crops are growing. Concentrations of only 5 ppm of 2,4-D will affect growth of susceptible plants, altho as a rule not herbicidally. Certain 2,4-D formulations, particularly the esters, are apt to volatilize and thus affect nearby crops. The sprays should be applied when the wind is low and in a direction away from areas of susceptible and desirable vegetation. 4. Preparations containing 2,4-D should not be stored with grain intended for seed purposes. Transfer of the chemical thru volatiliza- tion may result in abnormalities in the plants produced from the seed. 5. If possible, spray equipment should be assigned only for the use of 2,4-D, since it is so difficult to be sure that certain 2,4-D formu- lations have been cleaned from the equipment. "If the same sprayer must be used for both 2,4-D and other sprays on susceptible plants, wash the sprayer with tri-sodium phosphate solution (two-thirds ounce to the gallon), or household ammonia solution (1 part to 100 of water) allowing the solution to stand in the sprayer 36 to 48 hours. Follow by thoro rinsing, in either case. Hot water is preferable for these treatments. Metal sprayers are more readily cleaned than wooden tanks. The sodium, ammonium, and amine salts are more readily re- moved than the ester formulations, which have a miscible oil base." 2 1 From the 1947 and 1948 Reports of the Policy Committee on Herbicides of the North Central Weed Control Conference. 2 WILLARD, C. F., and WELTON, F. A., in Ohio Agr. Exp. Sta. Farm and Home Research 32, 33. 1947. 500 BULLETIN No. 525 [January, Chlorates Sodium chlorate has many drawbacks such as cost, its relatively long-time effect upon the soil, its effect on succeeding crops, and the hazards of handling it. Also, it is not always totally effective. In some cases, however, this chemical has actually proved 100 percent effective. Therefore, it still has a value when complete elimination of field bind- weed is desired in an area which cannot be reached by cultural equip- ment. Sodium chlorate has been tested both in its pure form and in the commercial preparation Atlacide, which is about 60 percent sodium chlorate. The pure sodium chlorate and Atlacide proved most promising in preliminary tests of different chemicals in 1936 at Urbana. The fol- lowing year, in an experiment comparing chemicals which had shown possibilities in the 1936 tests, the chlorates were the only chemicals to prove satisfactory (Table 15). Only two treatments of sodium chlorate or of Atlacide were necessary to destroy field bindweed. The chlorates proved equally effective in 1938 and 1939 (Table 16). Treatments those years were made not only to test various chemicals but also to actually eradicate all bindweed from an area. Thus, only chemicals that had previously shown any promise of effectiveness were used. As in the previous tests, the chlorates gave best results. Chlorates, at rates of 3 to 5 pounds per square rod, when properly applied will greatly weaken, if not kill, field bindweed. As long as the effect of chlorates is in the soil, any new seedlings will also be killed. Any bindweed seeds which do not germinate while the soil is sterile may later germinate and grow. Special precautions. It is highly important that treatment should extend 4 or 5 feet beyond the edge of visible infestation. In this way all roots and plants just ready to come up around the border will also be killed. Chlorates should not be applied to newly plowed or tilled land. After the soil has been treated, it should not be cultivated until the weeds have been fully eradicated. Repeated treatments may be less effective if the land is cultivated during the time when applications are being made. Danger in using chlorates. Neither sodium chlorate nor Atla- cide alone is dangerous; it is only when the chlorate comes in contact with dry material such as weeds, clothes, straw, or any combustible product that it provides a fire hazard. Then, if struck with a sharp blow, it will sometimes explode violently; or if ignited by friction or a spark, it will burn rapidly. 1948] ERADICATING FIELD BINDWEED 501 Original weeds still 2 i "a | CM o o CM CS ID CM 1/5 o CM CM CM CM m o O 00 s ooo PO CM CS lOOO n CM CS ' smelting industry). >duction in the area, i on the same dates 1 T-H 1 t^ CO treatments plot , ^-product o no seed prc were givei o\ r- 1 in 1 Number of per :- ' . '- ... . .Q ?1 e n* o-fi-o |aj "oilg hH cf 1 D T3 (!) Ov 00 CM a CM bi 3 o o O O > * CM t the treatrr il rates wer treatments o T3 , ^^5 '3 -""S nical Treatments i >P i - Same as P Same as P Same as P Same as P Same as P Same as P Same as P Same as P Same as P Same as P 1 ll CS CSCM III e with the equipment av -ates were doubled, since same dates as the three s n, Plot 1. 1 u 1 n 1-1 3 a H Material in 2 gallons of i 3 3 7 H D a 3 S 1 Sulfuric acid, 3 pounds* Arsenical solution, 200 cc 2 Sulfuric acid, 6 pounds* Arsenical solution, 300 cc : 3 Sulfuric acid, 1 pound* Arsenical solution, 100 cc 4 Iron sulfate, 1 pound 1 " Iron sulfate, 2 pounds 5 Iron sulfate, 2 pounds 1 " Iron sulfate, 4 pounds 6 Iron sulfate, 3 pounds 1 " Iron sulfate, 6 pounds ......' 7 Sodium thiocyanate, 1 pound 8 Sodium thiocyanate, 2 pounds 9 Sodium thiocyanate, 3 pounds T3-S-0 C C C 333 OOO oaa <-H CM1O S-S-S 'O'o'o O"-CM 3 Sodium chlorate, 1 pound 4 Sodium chlorate, 3 pounds 5 Sodium chlorate, 5 pounds * Sulfuric acid was so difficult to hand b After the first three treatments the he first three treatments were made on the the five treatments with arsenical solutic HS 502 BULLETIN No. 525 \January, Table 16. Chemical Treatments Used on Field Bindweed: Urbana, Illinois, 1938-1939 Plot 1938 1939 Results June 30, 1940 Material and date Amount per square rod Material and date Amount per square rod Ib. Ib. 1 Atlacide: .9 Sodium chlorate: 1.4 No bindweed Sept. 1, Oct. 26 > Oct. 19 2 Atlacide: 1.8 Sodium chlorate: 1.4 No bindweed Sept. 1 Oct. 19 3 Atlacide: 1.5 (No bindweed) No bindweed Sept. 1, Oct. 26 4 Atlacide: 2.0 (No bindweed) . No bindweed Sept. 1, Oct. 26 5 Sodium chlorate: 3.0 (No bindweed) No bindweed Sept. 1 ..- 6 Sodium chlorate: 4.1 (No bindweed) No bindweed . ' - Sept. 1 7 Lime chlorate: 1.8 (No bindweed) No bindweed Sept. 1, 17, Oct. 26 8 Lime chlorate: . 3.0 (No bindweed) No bindweed Sept. 1, 17 9 Ammonium thiocyanate: 3.0 Sodium chlorate: 4.7 No bindweed Sept. 1, Oct. 26" Oct. 19 10 Ammonium thiocyanate: 1.8 Sodium chlorate: 3.3 No bindweed Sept. 1, 17 Oct. 19 11 Ammonium thiocyanate: .9 Sodium chlorate: 2.4 No bindweed Sept. 1,17, 26" Oct. 19 12 Iron sulfate: 6.0 Iron sulfate: 6.0 Many plants Sept. 1, 22 Oct. 19 8 First-year treatments en these plots were not very effective. Since the bindweed, for practical 6ns, had to be completely killed, chlorates were used in 1939 on all but Plot 12. It is highly important to follow these rules when handling chlorates: 1. Keep the chemical in tightly covered metal containers. '2. Mix and handle material away from buildings. 3. Wash all clothing used in spraying before it dries. Since it is dif- ficult to remove the chemical from shoe leather, one should wear rubber boots, and these likewise should be washed before they dry. 4. Keep all fires away. Smoking even while wearing the clothing which was used in spraying is positively dangerous. 5. Thoroly wash all spraying equipment used for Bordeaux, lime- sulfur, or other sulfur sprays, before using it for chlorates. Sulfur forms an explosive mixture with chlorates. 6. Do not apply chlorates near valuable trees and shrubs, as the leaves may drop off or the plants may be killed. Effect on soil. Heavy applications of chlorates are likely to leave the soil sterile for one or two growing seasons, especially in years of low rainfall. In 1939 corn was planted on all plots chemi- cally treated in 1937-1938 (Table 17). Corn growing on the chlorate- treated plots showed the worst effects. By 1940, however, the corn on the chlorate-treated plots appeared normal. 1948] ERADICATING FIELD BINDWEED 503 Table 17. Yield of Corn on Soils Previously Treated With Chemical Herbicides: Urbana, Illinois, 1939 (For treatment and dates see Table 15) Type of chemical Plots* Corn hills Cornstalks Fodder Ear corn 123 number 48 number 117 Ib. 26 Ib. 58 Iron sulfate 4, 5, 6 48 149 42 88 Sodium thiocyanate 7, 8, 9 48 156 49 91 Atlacide 10, 11, 12 44 116 33 49 Sodium chlorate 13, 14, 15 45 128 . 30 46 "Plot numbers refer to those in Table 15. In addition to making the soil sterile, the chlorates are likely to cause puddling of the soil for some time. This is due to the accumu- lation of the sodium ion. When puddling occurs, a hard soil crust may result, causing low germination of small-seeded legumes the following year. When chlorates are applied in the fall, a normal yield of certain crops can sometimes be obtained the following year. More often the yield will be reduced, however, and occasionally no crop can be grown until the second year. Cost of chlorates. The price of chlorates in the past has ranged from 7 to 12 cents a pound, depending on the season and the amount purchased. At 10 cents a pound the cost of treating will range from $40 to $100 an acre. Chlorates have limited use. The cost of chlorates, together with the loss of the use of the land for one or two seasons, limits the use of chlorates to small areas. Chlorates should be used for (1) small spots in cultivated fields, pastures, and waste places; (2) fence rows near fields where weeds have been eradicated by tillage; and (3) road- sides and rough land where cultivation is impossible. Other Chemicals Among the other chemicals which have been tested at the Univer- sity of Illinois are sulfuric acid, an arsenical (by-product from the smelting industry), iron sulfate, and sodium thiocyanate. 1 These chemicals showed promise in the 1936 preliminary trials and were in- cluded in the series of plots which was set up in 1937 to compare types of chemicals (Table 15). 1 A complete list of the chemicals tried may be obtained by writing to the Agronomy Department, University of Illinois, Urbana. 504 BULLETIN No. 525 {January. Sulfuric acid was tested because of its cheapness and because of the possibility that it would kill the roots by repeatedly destroying the top growth. A "top-burner" type, it did not directly affect the roots. It was later replaced by the arsenical, which had the same effect on the plants. Iron sulfate, a "top-burner" chemical of a selective or differential nature, was tried with the hope that, by repeated treatments, it would destroy field bindweed without destroying grass. In the pre- liminary trials in 1936 fewer applications of sodium thiocyanate than of other chemicals had been needed to prevent all top growth. Accord- ingly, sodium thiocyanate was included in the 1937 tests. Altho none of these chemicals proved satisfactory, final results were not available when the 1938 tests were set up. Accordingly, ammonium thiocyanate and iron sulfate were included with the hope that they might eradicate field bindweed (Table 16). When it appeared that ammonium thiocyanate was not going to kill the bindweed, the treat- ment was changed to sodium chlorate. Only one plot, No. 12, was treated with iron sulfate; and even tho the applications were heavy, the bindweed was not killed. After-effects of chemicals. Corn planted in 1939 on plots which had been treated with iron sulfate or with sodium thiocyanate ap- peared normal when compared with surrounding corn (Table 17). Plots treated with the sulfuric acid-arsenical solution showed harmful effects not only in 1939 but also in 1940, when they were the only plots with residual effects. Early growth of corn in 1941 still appeared slightly reduced on these plots, but difference in growth was less notice- able later in the season. Arsenicals particularly dangerous. The effects of arsenicals are known to be cumulative in the soil, large amounts resulting in con- tinued soil sterility. "Arsenicals are also harmful to the operator. Thus, even if arsenicals were effective in eliminating field bindweed, which they have not proved to be, they could not be recommended. FINAL CHECK-UP NECESSARY Even after field bindweed is eliminated from a field, all the good work can soon be undone if surrounding infestations are allowed to spread. Ditchbanks, fence rows, and waste places should be checked for the presence of field bindweed. If it has appeared in any of these places, it should be eliminated at once. 1948} ERADICATING FIELD BINDWEED 505 Sometimes out-of-the-way infestations can best be eradicated by chemicals; other times the fence may be removed and cultural pro- cedures extended to the fence row areas. Individual plants scattered here and there should be eliminated, since the first infestation can easily start from just one seed or a single plant. Field bindweed seed can also be introduced in crop seeds, garden seeds, feeds, manures, neighborhood threshing machines, and other farm equipment. As much care as possible should be exercised to avoid a new infestation from these sources. SUMMARY Field bindweed is so prevalent in Illinois that serious efforts should be made to control it. Since the plant spreads both thru seeds and thru its root system, both must be eradicated before the plant can be controlled. Cultural methods of control. The established roots of field bind- weed can be eradicated in one and one-half to two growing seasons by bare- fallowing or by clean cultivation of an intertilled crop like corn. It is cheaper to use clean cultivation while growing corn than while growing soybeans. Cultural methods of control should be started in the spring before field bindweed blossoms, rather than in late summer or fall. Cultiva- tions should be made about 10 days after the bindweed plants emerge. This is the best time from the standpoint of both economy and effec- tiveness. The best depth of cultivation for both fallow and clean cultivation is that at which the cultivation instrument operates best usually 3 to 4 inches. A sweep-type cultivator with overlapping blades misses fewer plants than the disk or shovel types. After the roots have been eradicated, it is advisable to grow inter- tilled crops for at least one more year in order to get rid of all the seeds in the soil. Altho corn does not grow so well as small grains as the first crop after bare- fallow, adding 20-percent superphosphate to the soil will keep yields up to par. An application of 250 pounds an acre has given good results. Soil tests should be made, however, to find out how much is needed for a particular soil type. Bindweed seeds are long-lived, and once they lodge in the soil, the best way to eliminate them is to encourage them to grow so that the 506 BULLETIN No. 525 resulting seedlings can be destroyed. One shallow cultivation will de- stroy the seedlings if it is made before they are 2 weeks old. To prevent seed production, the plants must be cut close to the ground or other- wise destroyed as soon as, or before, the first blossoms appear. The combination of growing small grains and bare- fallowing after grain harvest is not a successful method. Chemical methods of control. Sprays containing 2,4-D may be used either alone or in combination with cultural methods. These chemi- cals have proved particularly effective in the prevention of seed production. One treatment of 2,4-D applied to field bindweed in the bud stage will keep seeds from forming. Chlorates have been effective in eradicating field bindweed and are recommended for very small areas and for places which cannot be reached with cultural equipment. Three to five pounds per square rod is needed. Prevention. Small infestations should be eradicated as soon as they appear ; the job can be done more cheaply then than at any later time. Special effort should be made to avoid introducing- field bindweed seed in crop seeds, garden seeds, feeds, manures, neighborhood thresh- ing machines, and other farm equipment. 10,0501-4836127 UNIVERSITY OF ILLINOIS-URBANA 30112018395779