UNIVERSITY OF CALIFORNIA California? college of agriculture Reserve AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA WALNUT CULTURE IN CALIFORNIA L. D. BATCHELOR Revised by L. D. BATCHELOR and O. LEE BRAUCHER BULLETIN 379 June, 1924 Revised October, 1929 UNIVERSITY OF CALIFORNIA PRINTING OFFICE BERKELEY, CALIFORNIA 1929 CONTENTS PAGE General review of the walnut industry 3 Consumption in the United States 4 Returns to be expected 7 Income derived from walnuts 10 Acreage 13 Length of life of walnut trees 14 Profitable bearing age of young trees 15 Climatic limitations 16 Frost injury 16 Heat injury 17 Soil requirements 18 Depth and character of soil 18 Drainage and alkali injury 19 Water requirements 20 Amount of irrigation water necessary 21 Irrigation water of good quality essential 22 Varieties 24 History 24 Choice of a variety 26 Rootstocks 41 Methods of propagation 43 Starting the Young Orchard 44 Requirements for good nursery trees 44 Planning the arrangement of the orchard 44 Care of trees before planting 46 Planting nursery trees 46 Planting the orchard with black walnut trees and top-grafting 48 Training young trees 51 Value of orchards and lands 57 Cultivation 60 Cover cropping 63 Irrigation 65 Intercropping , 80 Fertilization 85 Pruning 85 Insects and diseases 87 Codling moth 88 Aphis ■ 88 Combined control for aphis and codling moth 89 Red spider 89 Italian pear scale 89 Walnut blight (Bacterium juglandis Pierce) 90 Melaxuma 90 Crown gall (Pseudomonas tumefaciens) 93 Crown rot 94 Winter injury or die-back 97 Harvesting 98 Hulling 102 Washing 102 Dehydration 103 Sun-drving 108 Packing 108 Selling the crop 110 WALNUT CULTURE IN CALIFORNIA L. D. BATCHELORi Bevised by L. D. Batchelor and 0. Lee Braucher 2 GENERAL REVIEW OF THE WALNUT INDUSTRY The Persian walnut (Juglans regia), more commonly known as the English walnut, may be seen growing in nearly every county in the state of California. The commercial production of nuts, however, is centered mainly in southern California; in Los Angeles, Orange, Ventura, Santa Barbara, Riverside, and San Bernardino counties. In the central part of the state walnut culture is becoming important — in Santa Clara, San Joaquin, Contra Costa, Lake, Napa, Tulare, and Sonoma counties. At the present time, there are approximately 125,000 acres of walnut trees of various ages within the state. During the past decade walnuts have been one of the most staple and at the same time one of the most profitable crops which could be grown on such land and in such locations as are adapted to this crop. The importance of walnuts as an article of commerce is shown in table 1. The record of importation of walnuts from abroad together with the production in this country may be compared. The increasing importance is shown of both the imported and domestic walnuts as a source of food in this country. Inasmuch as the proportion of imported shelled nuts to those imported in the shells has increased greatly during the past decade, it is necessary to transpose all tonnage figures to the same basis. Other- wise the totals are not comparable. The total tonnage for each year is therefore stated in terms of walnuts in the shell, the kernel ton- nages being transposed into terms of unshelled nuts containing 45 per cent edible portion. An ordinary sample of commercial domestic nuts may be expected to contain 45 per cent edible portion. It should not be inferred from this that the transposed tonnage on the basis of 45 per cent edible portion represents the tonnage of walnuts which was cracked to obtain the imported kernels. The calculations are made in this way 1 Professor of Orchard Management in the Citrus Experiment Station and Graduate School of Tropical Agriculture, and Horticulturist in the Experiment Station. 2 Employed by the California Walnut Growers Association as a co-worker with the Horticultural Division of the Citrus Experiment Station. 4 University of California — Experiment Station merely to show approximately the tonnage of domestic nuts for which the imported kernels act as a substitute. The actual tonnage of for- eign nuts which was cracked to obtain the kernels as stated in table 1 was more nearly in the proportion of 3 to 1, as 32 per cent is more nearly the edible portion found in many of the European "cracking varieties. ' ' Walnuts, formerly looked upon as a holiday luxury, are becoming more and more a food to be used the year through in the average household. In table 1, column 6, the production of merchantable nuts in California is shown. It is apparent that there is a marked fluctuation in production from year to year according to the favorableness of the seasons. The trend in production obviously cannot be obtained by comparing the production for a single year with another single year. The production in 1919, for example, has been exceeded only twice during the nine years which have followed, and in only one year has the tonnage exceeded the 1919 production by a notable amount. This, however, does not give a true picture of the trend of production. If the average of the four-year period, 1915 to 1918 inclusive, is com- pared with the average production during 1925 to 1928 inclusive, a leveling effect will be obtained by averaging four years' production together in each instance. This average annual production in the first instance is 16,034 tons and the second instance is 26,841 ; this may be taken as a fairly reliable indication of an increase of 67 per cent during the past decade. The importations recorded in columns 2 to 5 inclusive of table 1 show a notable increase during the decade heretofore mentioned. The average annual imported tonnage of unshelled walnuts (column 5) has advanced from 22,059 tons to 34,784 tons, or an increase of 58 per cent, during the decade just past. This may not be a true picture of the trend of importations, however, because of the restriction of available shipping facilities during the World War. For this reason the figure 58 per cent is probably somewhat inflated. Consumption in the United States. — Taking the four years just past as a basis, the consumption of walnuts in the United States, as shown in columns 5 and 10 of table 1, has been divided between domestic production and importations in the proportion of 47 to 53. This is graphically shown in figure 1. On the basis of the edible por- tion of the nuts, the domestic production in the United States is slightly less than half the total consumption. In terms of walnuts in the shell, 45 per cent edible portion (page 5) the total annual consumption of walnuts in the United States has Buu 379] Walnut Culture in California TONS 80000 [777-, CALIFORNIA V//A PRODUCTION IMPORTATIONS OREGON PRODUCTION 7> ~ Vy " ^ ~ _1 70000 60000 50000 40000 30000 aoooo 10000 ■ 913 1914 1915 1916 1917 1918 1920 1921 1922 192} 1924 |925 Fig. 1. — Annual consumption of walnuts in the United States. Domestic and foreign tonnage sold as walnut kernels has been converted to the basis of unshelled nuts, 45 per cent edible portion, and added to the original tonnages sold as unshelled nuts. University of California — Experiment Station - i a $ O -H •- • cS Total sumpt in the ted St 10 CO IO t-l ^< CO co co i-H 00 O r^ O CM OS CM CM OS CM 00 OS CO ■* 10 CM lO t- t- ^M OS CO ^ CO N CM CO »o •* «o ■* t^ 0O t^ OS O t^ * N CO if) E OS CO CO O rt t^ CM O to ^H O IO CO CO CM O N 00 to CO CM ■* >jt n co O * 10 O 11) lO N >(5 N (O CO CO C -B o « « P j8 3 u -* O O 00 co co N ■* ■* us 10 CO H O N in) CO t- O O O CO T-H OS 113 ■* 00 CO CO f^ © CO •*»< t- O l>- >o os — — — -u d ^30 2.5 " TfH -** 1^-. CM rt O CO N » N IO OS IO 10 co t^ t~ CO «5 N N N N CO 'St fc : ? -H CM 1—1 1—1 fla £ t< cj 0) • "5*35 Total aductic chanta s in Ca OS c t^ co r^ O0 N CO H if) 115 ^ O rt O «d co a- .-1 -* cm 10 •rt OS CO -H O O I-- Tjl to » N N O •«n O >-^ oc OO » rt OC - X N Ol £N t~- CO 1^ ■«»< 1^ -H co os r- CC OS 0- CO -*< 00 "" 1— 1 co © >-i to O IO t- rt »o CO cu ■<1< CO CN Ol ■* K) !C CO O t-- OS i-H IO O iO O rt OS co CO 1- OH 00 .- O 00 CO lO OS CM rt CM co" rt CC a CO P 13 c J m JV c"^3 cu~ -* "*t co os cc i-H CO CM OS OO C IO «5 00 t^ "- CO CNl •*, N CO H OC O f~ i-H O t~- CO OS N ■* CC J^ -HH CO CM CC co to co t^ rt 10 00 O CO CO CO (O N "C CC 00 £"3 CD ^H OC ■<* to co c: 1— 1 t^ -h* OO O 1— CO* IO* rt" rt « co rt rt rt rt CNI CN CM CM CM CM 1- CM (i co l, ocS Osa T3 1-H C CM CM OS t* rt OS CO lO rt O" 00 -^ t^ >C 2 a> lO O O OS CM IT CO O CO O I*- O- t^ IO 00 C co 3 CM oc CO OS i-H OC i-H OS CO i-H 1— 1 to M IO N N r^ ^3 10 c CO O co" T* 10 n » 00 a a rt" rt" os" O- cC CO CO CO 00 CM OS OS U5 >o 03 a > s t 3 J* 2 1 g "3 co -h. i 10 » N Ol ) CS O H N CO H Ui CO 9 c fP 1 rtl CM CM CM CM CN CM CM CM CN > ■' > — • 1 s O 1 O j O . O O s O O s CJ CT B at cr 0- cr < < Bul. 379] Walnut Culture in California 7 ranged between 45,000 and 75,000 tons annually during the past few years. The consumption per capita has increased from approximately 0.745 of a pound (12 ounces) annually during the four-year period 1915 to 1918 inclusive to 1.110 pounds (17% ounces) as an average of the last four years 1925 to 1928 inclusive. This amounts to 49 per cent increase in per capita consumption during the decade just past. The trend of the annual consumption of walnuts per capita in United States is shown by figure 2. Year 1910 igi5 ig2 o Fig. 2. — Trend of the annual walnut consumption per capita in the United States. Calculated from data of figure 1. Returns to Be Expected. — The reasonable returns per pound of nuts which may be expected from a walnut grove may be forecast with some degree of confidence by a study of the trend in prices during the past, If such a study is to be put on a sound basis, the figures used must represent the average price per pound received by the growers for their total crop. The figures showing the wholesale market price per pound of certain of the higher-grade classes, after the nuts have been processed and packed, obviously give an erroneous and inflated value when used for the farm price. When such values are used to inflate the price of walnut-grove development subdivisions, the final result amounts to obtaining money under false pretenses. University of California — Experiment Station Per cent of total crop included in data — both seedling and budded walnuts oo Ratio of orchard-run to opening price, per cent t^ Value per pound net to grower orchard-run CO u 3-2 wa a -a a$ 03 O ■>*< Range of net orchard-run price in 19 local packing houses co WD ■a| o CM 03 ~ N K! tO C<5 >o <— i »C CO n O! m oo •— i — i co cm co «5 »/3 OS co >— i i-l <* ■* 00 t- cm os >o co co * n n ^i h lO i-H rH •>*< OS OS CO O OO oo © Os o o to r-- a^ ».o ->* co iO •-o CI o o SO •* t— .-c _, s to t^ OB to t— OS OS O o CI o »o 00 on iO to O o CO 00 00 Os SO OB N N "O CO ifl CM t Ji ■W™f^»WPC3^X»Sff* .'•;*" M ' W . ^W*™1 -..'..;.■:> ^;- HmW« ->oA^?i$MPV|j Fig. 6 — Eureka (natural size). 30 University of California — Experiment Station In an attempt to learn the cause of the existence of several differ- ent types, the ranch where this variety was first propagated was vis- ited during" the winter of 1924. In interviewing a member of the family who was present when the early propagation began, it was learned that there were originally four seedling trees from which this so-called Placentia Perfection was first propagated. Two of these trees furnished more scions than the others because they were con- sidered somewhat superior as regards productivity and nut character- istics. No attempt was ever made to keep the scions from the four trees separate, thus this so-called variety from the very beginning was really composed of four clonal varieties indiscriminately mixed together. It is therefore not surprising that many writers have com- mented upon the different types of Placentia. It may well be assumed that one of the four original seedlings is superior to the rest in pro- ductivity or blight resistance. There are, no doubt, many hetero- geneous Placentia groves from which scions are now being taken, which should be carefully gone over during harvest to eliminate the least desirable types. The two outstanding types most commonly found in the Placentia mixture, are a roundish type which produces a large percentage of rather rough nuts, and a more oval type which is composed almost exclusively of very smooth nuts. The former type is shown in figure 5, and is probably more commonly found than the latter type. The Placentia variety has been grown with marked success throughout the coastal sections of southern California, and some of the best grafted trees in the inland valleys of the south are of this variety. The placentia has not become popular with the walnut growers of central or northern California, because it seems to lose some of its tendency for precocity and heavy production, and is further hampered by its production of dark kernels in those districts. Eureka. 10 — This variety was originally selected because of its sup- posed resistance to walnut blight, the heavy production of the parent tree, and the exceedingly high quality of the nut. The supposed resistance to blight has not been substantiated. The Eureka is not usually so readily propagated upon the black walnut root as some of the Santa Barbara soft-shell varieties. The trees are vigorous growers, although the growth may not be so great 10 The parent tree of the original Eureka tree was a Persian or Kaghazi type of walnut which grew on the old Meek estate near Hayward, California. The seedling which developed into the original tree was located in the dooryard of a ranch about a mile south of Fullerton. Here it grew to be a mature tree, but died of a root disease during the summer of 1923. Bul. 379] Walnut Culture in California 31 1 ^iL*i V ft - J i i ! ; < /; ^^^^p^|Kf^«BP^ s : ! i^ « ,y?3i§ I lifi, * -■ -IP : Fig. 7. — Ehrhardt (natural size). 32 University of California — Experiment Station as that of the Placentias in the same orchard. The Eureka is later in reaching an age of profitable bearing than the Santa Barbara soft- shell varieties in southern California. The tree blooms much later than most other varieties and often escapes injury to the flowers by late spring frosts. Its harvest season is fully three weeks later than that of seedling nuts, or of the Placen- tia. This is a distinct disadvantage in marketing the crop in the eastern cities in time for the holiday trade. The Eureka variety has suffered a great deal from injury caused by being: frosted during the early fall. This may be due to a charac- teristic of late ripening, or to the possibility that the Eureka has been planted in places most subject to frost because of its late blooming habit. The Eureka nut is easily distinguished from any other variety grown in southern California by its pronounced elongation, rather straight parallel sides, slightly rounding to square ends, with the apex usually broader and more nearly square than the base (fig. 6). The color of its shell is a bright straw, of a lighter, more attractive shade than the typical soft-shell nuts. The extra heavy shell and the excep- tionally and completely firm "seal" of the nut, make it a model nut for good keeping qualities, and for withstanding commercial handling. A well-grown Eureka nut is filled to its full capacity with a light, cream-colored, plump, waxy kernel, with rather deep convolutions, possessing the very best of eating qualities. The Eureka is richer and freer from astringency than the soft-shell varieties. The kernel of the Eureka walnut will not usually fill out perfectly on all four quarters. For this reason the variety has been very dis- appointing in southern and some of the central California districts. Ehrhardt. 11 — The location of the original seedling tree from which this variety was propagated is apparently unknown. The Ehrhardt walnut is of the Santa Barbara soft-shell type, closely resembling in some ways the Placentia. It is somewhat rougher, slightly larger, and better sealed. The kernel gives the impression of being more plump than that of the Placentia, because its convolutions are very shallow. The variety is readily propagated, making a tree of medium vigor, which bears at an early age. It will probably succeed where the Santa Barbara soft-shell type succeeds. 11 For a detailed description and history of this variety the reader is referred to Batchelor, L. D. Walnut Culture in California. California Agr. Exp. Sta. Bui. 332:1-80. 1921. Bul. 379] Walnut Culture in California 33 Fig. 8. — Payne (natural size). 34 University of California — Experiment Station Its tendency to produce very heavy crops of high-grade nuts, apparently out-yielding the Placentia, makes this variety worthy of extended commercial planting, especially in the coastal districts of southern California. Several trees top-grafted to Ehrhardt have shown remarkable production in Santa Clara County. The nuts (fig. 7) are well considered by the wholesale trade. One of the distinct advantages of this variety is the fact that it so closely resembles the Placentia that it is sold with the latter variety in the budded grade. This simple wholesale disposal of a relatively new variety is a decided asset if it is to be planted in sections already largely devoted to the Placentia. Payne. — (Synonyms: Losee Payne, Cluster Mayette, Losee.) The parent seedling tree of this variety was discovered by G. P. Payne in his grove, near Campbell, California, in 1898. The variety has not been widely planted and only in recent years has it been propagated in any quantity. This variety somewhat resembles the Franquette regarding shape and eating qualities. Its precocity in reaching heavy production is probably the chief characteristic which has brought it into prominence during the past few years. In this respect it exceeds any other variety produced in the state. The Payne is notoriously subject to blight. The Payne tree makes a rather slow growth, possibly because of its very heavy production as a young tree. The nuts are borne rather prominently on the outside of the trees and are thus subject to severe sunburning in the inland valleys during years of abnormally high temperatures. The nut (fig. 8) is oblong, rather pointed at the apex; shell of medium thickness, somewhat pitted, and well sealed ; kernel full, with moderate convolutions, and of exceptionally mild flavor. With the heavy production of the oldest trees growing at present, there seems to be a reduction in the size of the nut, making a high percentage of small sizes. This nut has been sold in the Fancy grade, under its varietal name. It is well liked by the wholesale trade and usually brings as much or more than the Budded grade, on account of its especially fine quality. The greatest popularity of this variety is found in the Stockton, San Jose, and Concord districts. It might be suitable to interplant in a Franquette grove and for such use it may be of great value. Thus during the first ten or twelve years of the growth of the orchard, the total production would be more than doubled. After this period the Franquette trees will require all of the space. In the districts of Bul. 379] Walnut Culture in California 35 ^r ^^^% *" ?*«>. 'UuK fellr ^mM^%ik_ . ■■&%&«"^- S - :•£>' #* v ^ b@S^» .'*:-&&9^^ ^n^Bcj l^^#^%'':^^^ ^PiU*r t r -* Br X '"B Aj fc¥ X^|l : &&m ■ - /" Jf $m^r ^ r ■ ^| 1 ^K'°j<£'^^j -jf s~ /-jp. r't/P&t^^^r ■ ^^^H ^ vS, "\\j/"*^H $&*■ J- : ^2'"J'JMmJ r 'JK5Ki : fc 3H W-'/vrimm «fc •'■ '>■' '■ "*■ JvaS a/AwJmw IgB^hI*' > ^'^^B •r-«»^Cll(r ^^ft'^'iiil^H^. ~'«prvXt ' ^i'-sSm 7j£^ mk w h«Si ^'~~ ; Fig. 9. — Franquette (natural size). (From Bulletin 231). 36 University of California — Experiment Station the coastal counties where the blight is most regularly severe and prevalent, the Payne variety certainly cannot be recommended for permanent trees. Concord. — The Concord is one of the varieties most extensively planted in portions of California, especially in Contra Costa and Napa counties. In these districts it has proved to be a vigorous, thrifty tree, and an annual producer of medium-sized crops. The trees are fairly precocious. The nuts are elongated and somewhat pointed at the apex; the shell is rather smooth; the nuts are poorly sealed, the kernel fairly plump, with medium to deep convolutions, only medium light-colored and of good quality. This variety is not so well received by the wholesale trade as the Placentia, Ehrhardt, Franquette, or Payne. It is doubtful if it should be planted where the above-mentioned varieties will succeed. In southern California the Concord does not yield so well as the soft-shell varieties. Franquette. — This well-known commercial variety of France was introduced into that country in the section around Vinay, Isere, in 1810 12 by a man named Franquet. The original source of the variety is not known. Felix Gillet introduced it into California in 1871. The first noteworthy commercial planting of this variety in this state is the Vrcoman grove at Santa Rosa. In more recent years very suc- cessful groves of Franquettes have been developed in Santa Clara, Napa, and San Joaquin counties from scion wood originating in the Vrooman grove. Plantings in Oregon which trace their origin directly to the Vrooman grove have been a notable success. There are many so-called Franquette groves which do not trace back to the original introduction of this variety, and in reality they are not the true Franquette. Some of these misnamed collections have been the means of reflecting great discredit on this very meritorious variety. In other instances the misnamed collections are clearly some of the other varieties from France which have considerable merit, but it is doubtful whether they are as well adapted to central and northern California conditions as the true Franquette. In planting this variety in the future we believe great pains should be taken to obtain the pure strain from well-known high-producing trees. The Franquette should not be looked upon in any sense as a type ; on the contrary is a pure clonal variety of long standing, and can be perpetuated thus if care in scion selection is exercised. 12 Treyve, L. Quelle varietes de noix cultiver en Fl-ance. Vie a la Campagne 22(260) :52. 1925. Bul. 379] Walnut Culture in California 37 Fig. 10. — Grove (natural size), 38 University of California — Experiment Station This variety has been tested longer in central California than any other. It has many adherents in these sections because of its regular crops of moderate size and of excellent quality. It is less liable to produce dark kernels, due to high maximum temperatures, than the Santa Barbara soft-shell varieties. In southern California, the Franquette has not proved commercially successful. The Franquette is only a medium producer during the first ten years of its growth. It blooms very late, and the harvest season is too late for the most advantageous disposal of the crop for the eastern holiday trade. Owing to its late blooming it usually escapes injury by late spring frosts. The nut (fig. 9) is large, elongated, pointed, fairly smooth, and of a lighter, clearer and more attractive color than the soft-shell types. The shell is thin, but well sealed, and fairly well filled with a very light-colored, moderately plump kernel. The eating qualities of the Franquette are unsurpassed by any variety grown in California. The high quality of this nut makes it sell for a higher price than most other varieties grown in the state. Grove. — The Grove walmit has attracted attention throughout the neighborhood of the original tree, at Lawrence, California, where it is known locally by the name of its original owner, the late Mr. L. E. Grove. The original tree is a chance seedling, growing in the door- yard, and it was one year old when Mr. Grove came into possession of the place. Nothing has been learned about the parentage of this tree. It has an upright habit of growth with a striking amount of fruiting wood for the size of the tree. The tree blooms late, probably a little later than the Payne, while the nuts mature from October 1 to 15. The foliage is large and dense and the nuts have not been subject to sunburn. The tree and nut characteristics suggest that this tree may have some Franquette heritage. The nut (fig. 10) is of medium size, oval, somewhat pointed on the blossom end, exceptionally well sealed, with a heavy shell. The kernel is plump, with rather deep convolutions, and lighter colored than the Santa Barbara soft-shell type of nuts. The percentage of kernel in several random samples produced during the past three years has varied from 50 to 52 per cent. From 35 to 40 nuts of these samples weighed a pound. The most valuable characteristics of this variety are its precocity and heavy bearing, and the fine eating quality of its nuts, which are of a desirable commercial type. The Grove is worthy of commercial trial in central California, Buu 379] Walnut Culture in California 39 wmmmmmsBBm Fig. 11. — Blackmer (natural size). 40 University of California — Experiment Station Wasson. — The original Wasson tree is located in a grove on the highway between Ventura and Santa Paula about one mile east of the Saticoy road, on the property of Lee Hawley. The tree is now 45 years old, 35 feet high, and has a 60-foot spread. The orchard in which it is located was planted in 1885 from seed obtained from the original Sexton orchard near Santa Barbara. The Wasson is large and rather rough with the suture coming up full width to the stem end on one side and suddenly flattening out for a quarter of an inch or so on the other side. The nut is well sealed and the shell solid and hard. It will stand much more abuse in handling than the Placentia. The tree is precocious and bears relatively large crops. The Wasson is apparently adapted to the same sections as the Placentia. Pride of Ventura. — The Pride of Ventura is a selected type of Santa Barbara soft-shell seedling. The original tree is located in Ventura County near Ventura. It is precocious and bears heavily. The nuts are large, fairly smooth, and the shell is heavy and well sealed. The very limited plantings in Ventura County indicate its superiority for that particular section. It should be considered an untried variety for the interior sections. Blackmer. — This variety is also known as the Mautner, Westfall, Westphal, Meridian, Leib and Leib Special, Vaughn's Pride, and Money Maker. The original tree is still alive and is located two miles south of Meridian on the east bank of the Sacramento River. The nut (fig. 11) is large, long, and pointed. The shell is very light colored and bleaches easily. It has a heavy shell and is well sealed. The kernels are large, plump, good quality, and light colored. It is marketed as a fancy variety. The tree comes into bearing fairly early and bears heavy crops. It is a vigorous grower and consequently must be planted at greater distances than some of the slower-growing varieties. The Blackmer blooms comparatively early and may often be damaged by late spring frosts. The nuts ripen early in the fall, which is a decided asset. The Blackmer has been thoroughly tested in central California in recent years. In southern California it should be considered essen- tially an untried variety. Bul. 379] Walnut Culture in California 41 ROOTSTOCKS Northern California Black Walnuts. — The choice of rootstocks for the walnut has narrowed down during the past twenty years to a pre- dominating" preference for the northern California black walnut (Juglans calif ornica var. hindsii). The seed is shipped commercially by several agencies from central California for this purpose. Groups of dooryard and border trees usually furnish this seed. Some nursery- men in southern California have located and use seed from particu- larly vigorous black walnuts of this species, which have been planted locally. The seedlings from a group of such trees vary considerably, and in some instances certain trees are especially valued because of their tendency to produce uniform and vigorous seedlings. This variety of the species is resistant to some degree to the oak root fungus (Armillaria mellea) ; this, in fact, is probably its most valuable characteristic. Were it not for the presence of oak root fungus in some of the walnut-growing districts, the black walnut root- stock would not be of any particular advantage in comparison with the ordinary seedling rootstock of Persian walnut {Juglans regia). The hard-shell type of this latter species, which was heretofore com- mon in California, makes a large vigorous tree and has much to com- mend it where the oak root fungus does not occur. One of the greatest disadvantages in using the northern California black walnut as a rootstock is its susceptibility to crown rot (Phyto- phthora). This disease has become increasingly troublesome during the past decade. The matter is further complicated by the fact that the northern black walnut (Juglans calif ornica var. hindsii) is merely a variety of and is often confused with the southern California black walnut (J. calif ornica) 13 and the latter is especially susceptible to the crown rot. Plantings of both varieties occur in southern as well as northern California. Therefore there has been much confusion in the past in attempting to obtain a pure strain of the northern variety for rootstock purposes. The fact that seed came from northern California has not always been an assurance that the northern species was obtained. Southern California Black Walnut. — Large collections of Cali- fornia black walnuts may show trees typical of the northern variety and other trees typical of the southern form with many specimen trees representing various intermediate types. This very heterogeneous !3 Jepson, Willis Linn. The silva of California. Univ. California Memoirs 2:195. 1910. 42 University of California — Experiment Station species may, therefore, be considered to contain one type (Juglans calif ornica var. hindsii) which is distinctly arboreous in form, with a tall trunk and large fruit (l 1 /^ to 2 inches in diameter). This type makes a good graft union with most of the varieties of the Persian walnut. The other type (J. calif ornica) is more variable, generally branches near the ground, and assumes a more shrub-like habit of growth. It does not form a smooth graft union with the Persian walnut and has the added disadvantage of being very subject to crown rot. The graft union is characterized by an enlargement of the black root just below the graft union to two or three times the size of the Persian walnut directly above the graft union. This condition of growth produces a partially girdled condition and often is associated with a dwarfed condition of the trees, together with especially large crops in proportion to the size of the tree. A tendency to sucker profusely at the crown is another undesirable characteristic of the southern California black walnut. Hybrid BootstocJcs. — The Paradox-hybrid rootstock, which is a cross between the English and any of the black walnuts, makes a remarkably rapid growing tree. Mature trees may have a spread of 60 to 90 feet. The vigor of this first-generation hybrid has been mainly responsible for its popularity among some planters. Such trees in the past have not been produced in any large quantity and due to the difficulties in propagating hybrids it seems probable that their use in the future will be only in a restricted way. The increased vigor of the first-generation hybrid is not carried on to following generations; in fact, the first-generation hybrid trees are usually nearly barren, and their seedlings show many types of growth and vigor, making undesirable rootstocks. The Royal-hybrid walnut is a cross between the eastern black walnut and the California black walnut. It is thought by some that the second-generation Royal-hybrid is equal or even superior to the northern black walnut as a rootstock. There may be hybrid strains which justify this confidence, but it cannot be said that such superiority is universal. Seedlings from some of the Royal-hybrid trees produce uniformly vigorous trees, while those from others are variable and lack vigor. Probably the pollinating parent has much to do with this lack of consistency. Persian Walnut Seedlings. — The variability of the California black walnut, and thus the many disappointing results of its use as a root- stock, as heretofore discussed, has been the means of turning the attention of the industry to the use of the seedlings of the Persian Bul. 379] Walnut Culture in California 43 walnut (Juglans regia) as a rootstock. If the seedlings are grown from especially vigorous trees, such as the hard-shell variety, we know of no disadvantage in using them wherever the oak root fungus is not a consideration. They have the advantage of making a smooth graft union free from any girdling effect, and are also apparently much more resistant, under orchard conditions, to crown rot than the black root. This latter characteristic has been its principal reason for popularity in several of the districts of southern California where the root-rot has become increasingly troublesome during the past decade. It was thought at one time that possibly the black walnuts of the several species were more resistant to unfavorable soil conditions than the Persian walnut. In the case of alkali soils the blacks have been recommended for use. During the past few years many walnut groves have been injured by using irrigation water containing harmful amounts of alkali. In observing many such groves it is apparent that the black walnut does not show any greater resistance to injury than the seedling Persian trees on their own roots. Increasing use of the Persian seedlings for rootstock purposes seems entirely justified. METHODS OF PROPAGATION^ The English walnut is usually grafted on to the black walnut root during the early spring, using a whip graft. It can be budded 15 however, and some nurserymen prefer this method. Grafting. — One year from the time of planting the nuts in the nursery the seedlings should be ready for grafting. By this time they should have attained a diameter of one inch or more at the surface of the ground. The surface soil is hoed away from the crown of the trees to a depth of 2 or 3 inches and the scion is inserted in the stock just below the surface of the ground. After the scion is tied and thoroughly waxed, the soil is hoed back over the crown of the tree covering scion and all to a depth of one or two inches. Well-pulverized soil is essential in covering up the grafted trees for the presence of 14 Stahl, J. L. Propagation of deciduous fruits. California Agr. Exp. Sta. Cir. 294:1-24. 1925. is The question is often asked: "What is a budded walnut?" The grade of nuts sold under the name ' ' budded ' ' has no doubt prompted this question in many instances. A budded nut is any one of the varieties which will grade according to the standard of perfection set by the Placentia. The tree which bears such a nut has been produced by budding or grafting a bud or scion of the variety in question on a seedling rootstock. If budded, the work is usually done in August, using a patch or a shield bud from the current season's growth. 44 University of California — Experiment Station clods is likely to result in the scions being loosened or knocked out of the stock. The grafted trees are grown one year in the nursery and trained to a whip-like growth free from lateral branches. It is necessary to tie each tree to a stake. Stakes 1 in. by 2 in. by 8 feet long make satis- factory supports. Considerable pains is necessary throughout the growing season to tie up the rapid growing trees periodically so they will continue to grow straight. Budding. — When walnuts are propagated by budding, the nuts are given an early start and the seedlings kept rapidly growing until August. At this season they are large enough to receive a bud near the surface of the ground. Patch budding is the method most com- monly followed, although a shield bud may be successfully used if the chip of wood is carefully removed from the bud. It is essential to have the bud ripened by removing the leaf, leaving the petiole attached to the base of the bud for a period of about 10 days before the buds are cut. After the buds are inserted in the stock they are firmly tied in place by means of waxed cloth. This must be loosened at about ten- day intervals until the buds have become attached to the stock. The buds are usually allowed to remain dormant until the following spring. STARTING THE YOUNG ORCHARD Requirements for Good Nursery Trees. — Grafted trees sell accord- ing to size, a premium being placed upon the larger trees. The price of well-grown walnut trees varies from $1.00 to $2.00. A medium- sized tree (8 to 10 feet) may be preferable to either an extremely large, or a small tree. A very large tree may be injured considerably in digging from the nursery, while a small one may be stunted, with a poor root system, and never make a first-class orchard tree. Although a considerable premium is usually paid for the largest trees, it is doubt- ful if they are actually worth any more than those of medium size. Planning the arrangement of the Orchard. — From 12 to 27 walnut trees to the acre are found in the mature orchards. General observa- tion and the opinions of many walnut growers agree that the trees have in the past, been planted too close in walnut groves in general. Orchards planted with the trees 60 feet apart each way are among the most productive in the state. With this spacing the individual trees have room to develop fully. A large proportion of the nuts are produced on the side branches, and the trees maintain a healthy vigorous growth of new fruiting wood for many years. Bul.. 379] Walnut Culture in California 45 Fig. 12. — The trees in this orchard were planted too close, being spaced 40 feet. They are producing walnuts only in the tops and will soon have to be thinned in order to obtain a satisfactory yield per acre. (From Bulletin 332.) Fig. 13. — An old seedling grove thinned out by removing every other diagonal row. 46 University of California — Experiment Station In the close plantings, where the trees are only 40 to 50 feet apart, the side branches are shaded most of the day, the fruit spurs on the lower branches soon die, and the crop is borne mainly in the tops of the trees. A closely planted grove is illustrated by figure 12. Such orchards have not maintained their productivity so well as those planted less densely. Plantings where the trees are 40 or 45 feet apart can be thinned out by removing every other tree in each row so that the trees alternate, or stand opposite a space in the adjacent rows. This is the same as removing every other diagonal row. The remaining trees will then stand approximately 57 or 63 feet apart respectively in the rows, running diagonally across the orchard. See figure 13. One of the most favored systems at present is to plant the trees 30 feet apart in rows which are 60 feet apart. The trees may be all of one variety, or of two, planted alternately. With the latter method, there is the advantage of a choice between two varieties when the time arrives for removing half of the trees. Such plantings are usually thinned out when the trees are from 10 to 14 years old, the time vary- ing according to the variety, soil, water and climatic conditions. They should not be left until they crowd badly. If this method is properly carried out, nearly twice the tonnage may be expected during the first 10 or 14 years as where only the permanent trees are planted. At the same time, there is practically as much room for intercrops such as beans, during the early life of the orchard as if only 12 trees had been planted to the acre. The extra expense of buying and planting filler trees may be paid for by part of one year's crop, while all other extra expense due to the filler trees, such as pruning, extra water, etc., is of minor importance. Care of Trees Before Planting. — If the trees are received from the nursery before the ground is ready for planting, they should be unpacked and heeled in where they will be shaded. The soil around the roots should be thoroughly watered after they are heeled in. If it is more practical, the trees may be held for a time under a shed with the roots packed in damp sawdust or shavings. Planting Nursery Trees. — Walnut trees should be planted during January or February so that the soil may be thoroughly settled around the roots and growth start with the beginning of the normal growing season, which is usually March in southern California. Holes should be dug deep enough to allow room for the full length of the tap root, which may be from 18 to 30 inches. The lateral roots may be 6 or 8 inches long, and the hole should be wide enough to accommodate them. Buu 379] Walnut Culture in California 47 Fig. 14. — Example of side and bark graft scions tied in place ready for waxing. 48 University of California — Experiment Station In filling in the soil around the roots, it is advisable to use the top soil, tamping it thoroughly without bruising the roots. A better stand of trees may be expected, and a prompter growth in the spring, if the young trees are thoroughly irrigated as soon as they are planted. This can be accomplished by running a single furrow along the row and cutting the water in at the basin left around each tree when it was planted. Irrigation at this time may not be essential from the point of view of available soil moisture but it will be well worth the extra care, as a means of thoroughly settling the soil around the roots to prevent their drying out. A few light rains should not mislead the planter and cause him to omit this first irrigation at planting. Planting the Orchard with Black Walnut Trees and Top-Grafting. — In several parts of central California, especially in Contra Costa County, the planting of nursery-grown walnut trees has frequently been followed by a rather poor stand, and a slow growth of the surviv- ing trees during the first 2 or 3 years. Walnuts are usually grown in this district without irrigation water and it seems probable that the poor results with nursery trees is directly traceable to the failure to water the trees at the time they are planted. In any event the past experiences have led the present planters to favor the planting of the black walnuts in the field and top-grafting the resulting trees when they are from 2 to 5 years old. Two or three walnuts are planted in each place where a tree is to grow. During the early summer the smallest trees from each group are pulled out, leaving the most vigorous one. In the Stockton and Linden districts one-year-old black walnut trees are planted in orchard form, rather than nuts. With good soil conditions and water available, black walnut trees or nursery-grafted trees should be readily transplanted with nearly all making a good growth the first year. Various methods of top-grafting are recommended by the advocates of this general method of starting a walnut orchard. The two-year-old trees may be grafted in the main limbs near the trunk by means of a side-graft. If the trees are 3 to 5 years old they may be top-grafted by means of a bark graft or a cleft graft. Figures 14 and 15 show the detail method of making side, bark, and cleft grafts. The particular type of graft best suited to this method of propagation depends largely on the size of the stock and the scion. The side graft is pref- erable on small branches, and the bark-graft or the cleft-graft method is the most usable on limbs 3 to 6 inches in diameter. Buu 379] Walnut Culture in California 49 Whatever method of grafting is practiced, one of the most import- ant details of this operation is in regard to waxing. All cut portions of the stock and scion should be covered with wax as soon as the scions have been tied in place. A hot wax made from the following formula is commonly used : resin 4 parts, beeswax 1 part, linseed oil 1 part. Fig. 15. — Cleft graft ready to wax. There are also prepared waxes on the market which are not so apt to crack with weathering as wax made according to the above formula. Bi-weekly inspection and rewaxing to keep all the cracks in the wax covered over is essential to success. Water-emulsified asphalt com- pounds make a satisfactory grafting wax. These compounds are used cold. Patch-budding is another method sometimes followed in top- working young black walnut trees. Two-year-old trees with one-year- old frame work branches % to % of & n inch in diameter are an ideal size to top-work by patch budding. The buds are usually placed in the branches, about 6 to 12 inches from the main trunk. With the 50 University of California — Experiment Station buds thus placed the eventual orchard tree has a trunk and the base of the scaffold limbs of the black walnut as shown in figure 16. The black walnut wood is stronger than the English walnut — an advantage in favor of such top-worked trees. v 5 )Jk J'K)' j ~\ o 1 a 4 t? i 3 1 NUT O r> O < // MAY 21 3/ 10 ^une 20 30 JULY /o Fig. 25. — Mean weekly growth of Placentia walnuts from May 3 to July 12, 1923. (Expressed as the area of the cross section, which is in direct relation to volume.) The most rapid growth of the walnuts takes place during the five or six weeks immediately after the blossoming period. It has been shown by field trials and by general observation that a shortage of soil moisture in a walnut grove during the early part of the growing period will be followed by a production of a large percentage of small walnuts. A study of the growth of Placentia walnuts was made during the 1923 season, the results of which are shown graphically by figure 25. The production of a large percentage of large nuts is so essential to successful walnut culture, that the details of the obser- 70 University of California — Experiment Station vations set forth in figure 25 may well be included in a consideration of the irrigation needs of this crop. Just when this period of rapid growth takes place and when it ends, is of prime importance to the walnut grower. At the end of the rapid growth "the die is cast" so far as the size of the walnut then on the tree is concerned. No amount of mid-summer or late irrigation water will make a particle of difference in the size of walnuts after the shell begins to harden so that it is cut with difficulty with a knife. In obtaining the data presented in figure 25 random samples of 100 nuts were picked weekly in a similar, careful, systematic manner from a group of Placentia trees. These nuts were cut across their largest diameter between the stem and blossom end. Records were kept of the average size of the nuts, as well as of the average size of nuts and shuck combined, for the growing season. The actual diame- ter measurements have been transformed into cross-section measure- ments to show more clearly the trend of growth. The curve shows the relative growth from May 3 to July 12. The trees bloomed 10 to 14 days before the observations commenced, at which time the small nuts were 1.2 centimeters (% 6 of an inch) in diameter. The curve shows that a rapid increase in size of the nuts took place from May 3 to May 31. After May 31 the curve flattens out and only a small growth is made up to June 28. After June 28 the differences in average size of all the samples measured were within the range of probable error in random sampling, and therefore show no increase in size after that date. The shuck, however, which cor- responds to the edible portion of a stone fruit, made more relatively late growth than the nut: the growth curve for the shuck did not flatten out much until the last of June. By June 14 the average size of the sample was equivalent to the minimum size of a Large Budded nut. By again referring to the curve it may be clearly seen how little actual growth took place after this size was reached. The cross-section size of the samples of Placentia walnuts increased 483 per cent during the 28 days from May 3 to May 31 ; and increased only 18 per cent during the following 28 days. It must be clear from these figures that any irrigation water which is to affect the size of walnuts should be in the ground during the month of May, and the earlier it is applied during the month, the more effective it will be. The winter irrigation serves also to supply the needed early spring moisture for the growth of the trees. Aside from the small amount of Bul. 379] Walnut Culture in California 71 moisture transpired by the dormant trees and lost through the surface evaporation of the soil, the bulk of the winter irrigation water is available for the tree's use in the spring, provided it is not largely used by cover crops or weeds before the trees begin to grow. Observa- tions of the soil moisture present by means of a soil auger or soil tube which will reach to depths of 7 or 8 feet, should at least begin at the time when the trees start to leaf out. If the winter rains plus the winter irrigation do not percolate to a depth of eight feet during the winter and late spring, it is advisable to apply the first spring irriga- tion sometime in April. At this season of the year the trees are begin- ning to leaf out and the young nuts should soon be rapidly increasing in size. Filling the subsoil with moisture at this season makes a reservoir for the tree roots to draw upon during the early part of the summer, while the nuts are reaching their full size. It should not be inferred from this that soil moisture which penetrates below the root zone is drawn upward into the root zone by capillary action as the growing season advances. Such capillary action is probably negligi- ble unless a water table is present. A series of experiments carried on by La Rue and Batchelor 16 points out the results of adequate irrigation in contrast to lack of proper irrigation in relation to seasonal growth. Three plots were laid out, comparable with the three conditions which are often found in commercial orchards. In one plot (plot 3) the soil moisture was maintained between the wilting point and field capacity of the soil to a depth of seven feet except possibly during the harvest season and early winter. In another plot (plot 4) the soil moisture was maintained between the wilting point and field capacity of the soil to a depth of seven feet except from the first week in July until the first week in September. During this latter period the soil was allowed to become dry. In still another plot (plot 5) the soil moisture was maintained between the wilting point and field capacity of the soil to a depth of seven feet, from July to September inclusive. This plot was therefore relatively dry during the first part of the growing season. All three plots received the same total amount of water. The effect of these three irrigation practices upon the nuts from the respective plots is shown in table 10, and may be summed up as follows : i !6 La Eue, R. G., and L. D. Batchelor. Irrigation of walnut trees in relation to the quality of the nuts. Diamond Walnut News, 10(2) : 3. May, 1928. 72 University of California — Experiment Station Plot 3, in which adequate moisture was available at all times, produced a good crop, in consideration of the adverse season, with respect to both size and quality of the nuts. Plot 5, which received no water until July, produced only 18 per cent large-sized nuts in contrast to 64 per cent large-sized nuts on plot 3, and 21 per cent babies as against 2 per cent babies on plot 3. The quality as compared with plot 3 was fairly good. There were 27 per cent culls on plot 4 and 26 per cent culls on plot 5 due to exterior appearance as con- trasted with 17 per cent culls due to exterior appearance on plot 3. Crack tests showed 26 per cent blanks, shrivels, and molded combined on plot 4 as against 14 per cent on plot 3. The results from the irrigation applied in early spring were not so good as in the case where the irrigation was applied in the winter prior to the starting of spring growth. TABLE 10 Percentage of Sizes and Quality of Walnuts Kesulting from Different Seasonal Applications of Irrigation Water. Nature of season of irrigation Packing-house grades Orchard-run crack test eliminating class in column 5 Size grade Culls exterior appear- ance Plot Culls, moldy, blank, and shriveled Baby Medium Large Sound 1 2 3 5 6 6 7 8 3 Adequate through growing 2 3 21 17 20 35 64 50 18 17 27 26 14 26 15 86 4 5 Dry latter part growing sea- son Dry early part growing sea- 74 85 The lack of soil moisture early in the growing season caused small- sized nuts, and the lack of soil moisture during June and early July resulted in very poor quality as measured by the shriveling of the kernels. Table 11 shows the yield and estimated gross income for each plot. Depth of Soil to Irrigate. — It should be the aim of the walnut grower to keep all the soil from the surface to a depth of at least seven to eight feet well supplied with moisture from early spring until early fall. In accomplishing this it should be borne in mind that the root system of the walnut tree is distributed throughout this entire seven Bul. 379] Walnut Culture in California 73 to eight-foot depth of soil and in many cases much deeper. How- ever, the soil moisture is extracted much more rapidly from the sur- face three or four feet of soil than from the area below this where the roots are less numerous. Such observations may be interpreted as showing that the roots are more numerous in the upper three or four feet of soil than in the area below this. For this reason it may be desirable to apply only sufficient water to wet the upper root zone at one or more of the irrigations during the summer months. This principle applies especially where there is little or no change in the water-holding capacity of the soil from the surface to the lower root zone. If, on the contrary, the lower portion of the root system is surrounded by a soil with a much greater capacity to hold moisture than the surface soil, it may be necessary to use precaution to prevent excessive irrigation of the lower root zone. TABLE 11 Yieild and Estimated Gross Income per Acre for Each Plot Plot Yield in pounds Estimated gross return per acre Loss due to unsea- sonal irrigation compared with plot 3 3 1,760 1,230 1 188 $357.28 194.46 167.75 4 5 162.82 189.53 Figure 26 shows the trend of soil moisture in a full-bearing walnut grove located in the coastal district, growing on a Yolo loam. The water-holding capacity does not change greatly throughout the first seven feet from the surface. It can be seen from this figure that the soil moisture was not removed as rapidly from the lower root zone as from that portion nearer the surface. The winter and early spring irrigations thoroughly wet the entire root zone, but it was not neces- sary to apply so much water during the latter part of the growing season as was applied during the winter irrigation. The slower drying out of the soil through the lower root zone made very heavy applications during midsummer unnecessary. The whole soil mass was kept above the wilting point throughout the growing season. In the case of groves located on such soil types as the Hanf ord fine sandy loam or the Hanford sandy loam, the conditions are different from the case above described on the Yolo soil. The Hanford types are commonly underlain by a coarse sandy strata which holds less water than the surface soil. With fewer roots in this lower area it will 74 University of California — Experiment Station o w o ifl omom ouiolo omoLnomoinotnot/) m o m o r* — — im "• —