- A.- \ \ Division of Agricultural Sciences UNIVERSITY OF CALIFORNIA THE ORIENTAL FRUIT MOTH IN CALIFORNIA F. M. Summers CALIFORNIA AGRICULTURAL Experiment Station Extension Service 11111:11111 CIRCULAR 539 Tie Oriental fruit moth, a serious pest on peaches and nectarines in Cali- fornia since 1954, can be controlled but infestation is often discovered too late to prevent damage at costs that are worthwhile to the grower. This circular provides information that will help the grower determine in- festation in time, so that he can undertake the appropriate control steps. The circular does not give specific pesticide recommendations and, for up-to-date information, refers the reader to the most recent Pest Control Guide for Peaches and Nectarines published annually by the University of California Experiment Station and Extension Service. August, 1966 THE AUTHOR: F. M. Summers is Professor of Entomology and Entomologist in the Agri- cultural Experiment Station, Davis. THE ORIENTAL FRUIT MOTH IN CALIFORNIA Where the moth came from The Oriental fruit moth, Grapholitha molesta (Busck), has been found in Aus- tralia, Japan, Manchuria, Korea, Italy, France, Canada and, since 1916, in the United States. It first appeared in the vicinity of Washington, D.C., probably imported from Japan. It had arrived in Japan from some other part of the Orient early this century. In the United States the moth spread northeast, south and west. It was found in Connecticut in 1917, in Georgia in 1923, and as far west as Missouri in 1930. By that time, fourteen years after its arrival in this country, the pest had be- come prevalent in practically all peach- producing states east of the Mississippi River. The seriousness of the crop dam- age induced federal and many state ex- periment stations to study the moth's bi- ology and possible control measures. California was one of the last peach- crowing states to be invaded by the fruit inoth. In spite of quarantine regulations and rigid border and maritime port in- spections, the moth entered California in 1942 and was first discovered in a small peach orchard in Yorba Linda, Orange County. During the next three years a state- wide survey disclosed traces of the pest (one or a few moths) in all the principal peach-growing areas of the state, but no outbreak took place. On the contrary, the numbers of moths decreased until, in 1947, it was difficult to find even a single specimen. The first serious outbreak occurred in 1954, in two separate peach-growing localities in central California. A con- siderable number of orchards were in- fested heavily, a few very seriously. Within two to three years, outbreaks be- gan to occur in the prime cling peach orchards of the two interior valleys. Al- though some large areas are not known to be infested now, the present distribu- tion of the moth is so extensive that its appearance may be anticipated wherever favored host plants are grown. Host plants for the moth The preferred host of the Oriental fruit moth is fruiting quince, but the principal commercial crop attacked is peach. Other economically important hosts include almond, apple, apricot, cherry, nectarine, pear, and plum. It has also been demon- strated experimentally that the pest can complete its development on fruits or flower parts of several ornamental trees and shrubs. How much damage? It is difficult to evaluate concisely the economic effects of the Oriental fruit moth on California fruit crops because costs are affected by too many direct and indirect factors. However, a review of these factors will help clarify the problem. Without doubt, Oriental fruit moth damage to peaches is serious. Before DDT was available as an insecticide, the moth was regarded as one of the most destructive pests on fruit crops. Experi- ment stations in the peach belt recorded serious losses, some as high as 100 per cent for certain varieties of peaches in particular orchards. In 1930, for example, the fruit moth damaged and rendered un- fit for marketing 12 per cent of the state- wide peach crop of South Carolina. To- day, because synthetic pesticides are available, the economics of the problem would probably emphasize the cost of control rather than crop losses. At present, the full impact of the moth on California horticulture cannot be ap- preciated because, except for peaches and nectarines, the major stone and pome fruits have shown no significant losses; but they may be potentially vulnerable. The moth may be able, in time, to adapt its reproductive capability for buildup and survival in almond, apricot, plum, and prune orchards but today these crops [3] are not seriously imperiled. Some fruit infestations have been found, usually on crops close to or bordering heavily in- fested peach orchards. Damage to peaches. The Oriental fruit moth does its damage through its worms (larval stage). The pest, like the peach twig borer, feeds primarily on the twigs and does not appreciably attack green fruit unless the pest population is very heavy or the growing shoots mature and become woody. The destruction of too many twig tips on very young trees causes abnormal branching and pruning complications; the effect on twigs of ma- ture trees is relatively unimportant. Canning peaches are most seriously af- fected, possibly because they are not picked until fully ripe. Successively ripening varieties of cling peaches are harvested at close intervals from about July 10 until September 3. All varieties are susceptible in some degree, but par- ticularly those picked during August and early September, for example Gaume, Carolyn, Halford, and Starn. During the first serious outbreak, at Kingsburg, Fresno County, approximately 55 or- chards were found to be infested, with decreasing seriousness the farther they were from an epicenter or "hot spot/' In the most seriously infested area, the crop of one orchard was a total loss — meaning that it was not economically worthwhile to pick and sort although much less than 100 per cent of the fruit was infested. Nearby orchards had one or more truck- lots rejected at grading stations, and all others had some fruit loss in addition to unusually high labor costs for sorting fruits. But dessert peaches picked in an orchard adjacent to the one having the total loss were relatively worm-free. They were harvested one month earlier, in semiripe condition for shipment to distant markets. Infested freestone peach orchards with late-ripening varieties also have had some crippling losses. Packers discard culls and credit producers for saleable fruit, generally on a pack-out basis. A different system prevails in the grading of cling peaches consigned to canneries. Producers sort to grade before delivery. Lots routed from orchards to canneries are subject to inspection at official way- side grading stations. This grading sys- tem may bring about a costly complica- tion with peaches damaged by the fruit moth. Fruit shipments may be passed in grade bv authorized graders and yet have "invisible" worm damage, that is, small, inconspicuous entry holes, so that dam- age is revealed only when fruits are peeled and split in canneries. With han- dling and transportation costs high, the growers of canning peaches face the hazard of total loss on imperfectly sorted shipments. The costs of returning, un- loading and resorting a rejected lot mav be prohibitive. Control of the Oriental fruit moth is sometimes complicated by late-season up- surges of worms, making necessary extra spraying or dusting of orchards. Dusting mav have undesirable side-effects such as drift of the pesticide to other crops, dam- age to apiaries, interference with visi- bility on highways, and increase of spider mite infestations. The prevalence of a similar pest, the peach twig borer, in California peach or- chards further complicates the assess- ment of fruit losses and pest control costs attributable to fruit moth only. If one learns to estimate levels of fruit moth infestation and determines appro- priate times for spraying, it should be possible to develop a program of insect control to fit the need. The remainder of - this circular is designed to help growers plan their control program, if needed, by describing: • The life cycle of the pest. • How infestations spread. • How to judge infestations and the , best time for spraying. [4] LIFE CYCLE Stem of a peach shoot stripped and peeled open to show a nearly mature worm within its mine. The stages of development The adult (moth stage) of the Oriental fruit moth is rarely seen in the orchard unless a special attempt is made to cap- ture it in a trap. The moth does not directly injure foliage or fruit; the adults neither bite nor pierce host plants and are equipped only to lap or suck up sur- face liquids such as dew or plant secre- tions. It is the larvae or "worms" that cause all the damage to crops. The moths are small, having a wing- spread of about J2 inch. The body and upper wing surfaces are dark gray, with superimposed tinges of bronze. Their only distinctive marking is a faint, nar- row band of silver gray forming an in- verted "V" across the middle of the fore- wings when they are folded. The moths rest on dark parts of the host during bright daylight hours. They normally be- gin to fly at dusk and continue until about midnight. Another period of flight activity comes before or just after day- break. During favorable weather the moths mate within 24 hours after emerg- ing from the pupal stage and begin to lay eggs within 48 hours. The eggs are laid on leaves, small twigs, or fruits. The laying period for a female continues for as long as 18 days. During this time 125 to 150 eggs may be laid, approximately two-thirds of them during the first eight days. Few eggs are laid at 60° F and none at 55° F or below. The eggs are tiny, convex, circular discs cemented to plant surfaces. They are approximately Mc inch across and are milky white until the embryo is well formed. They usually hatch within three and one-half to six days in midsummer and within seven to 14 days when night- time temperatures stay close to 60° F. A "strike" or "nagged shoot." The terminal shoot and one of the laterals have been bored out, probably by the same worm. The dried remnants indicate depth of mines. This is an old strike; the worm has matured and crawled elsewhere to pupate. This damage is indistinguishable from that done by the peach twig borer. [5] This Elberta peach has been badly damaged inside, close to the pit. The only outward indication is the tiny entrance hole of the worm near the base of the stem. The smallest larvae (worms) are about Vie inch long and have black heads and almost transparent bodies. When they bore into buds or fruits, the entrance is so small that very sharp vision is required to find it. As worms feed they grow for a time and then molt; they repeat this growing and molting for four or occa- sionally five growth phases, each one longer than the preceding. Full-grown worms are approximately % inch long and cream, flesh-colored, or faintly pink in body color. The head capsule is yellowish brown. When full grown, they almost always leave their twig mines or tunnels in fruit and crawl to suitable niches in which to spin cocoons. It is the exit hole in fruits which indicates damage; this hole often fills with semihard gum. Many of the worms lower themselves directly to the ground by secreting a silk strand. In orchards, the cocoons are constructed deep in the cracks of thick tree bark, in pruning scars, under leaf trash, in the ground, and on remnants of dry weeds. The pupa is the complex transforming stage. Most of the organs of the larva are refashioned into the form of a reproduc- tive individual, the moth. The overwintering stage The Oriental fruit moth, like the codling moth of apples and pears, ends its season of activity when some of its larvae stop developing and go into hibernation. Under California conditions, a small num- ber of these hibernating larvae appear during the third summer generation in June and July; a much larger number of fourth-generation larvae cease to develop in July and August. All larvae of the fifth generation, in September and October, become part of the total overwintering population. A substantial fifth generation of larvae occurs in the interior valleys but not in southern California. This overwintering stage enables the pest to endure the stresses of winter and thus protects the species during the long period when host plants are dormant. It is in this state that larvae hibernating on nursery stock or in picking boxes are readily dispersed to orchards. It is also the stage least responsive to sprays. [6] Larvae destined to hibernate resemble those which immediately transform into moths and start another generation, ex- cept that their internal gland functions are different. All larvae grow to full size in fruit or twigs, then leave the food source and wander in search of suitable places in which to spin thick-walled silk cocoons. As soon as the cocoon is con- structed, nonhibernating larvae become rigid and immediately change into pupae. About 10 days later the pupal skins split and moths emerge from the cocoon. Those destined to overwinter do not pupate immediately, but persist as larvae until spring. Certain variations in temperature and length of day are required to end the hibernation. Some of the larvae resume development and pupate as early as the end of February; most end hibernation during early March; and a few "strag- glers" do not become moths until April. The period required for all of the moths to emerge is approximately 45 days. The first moths appear when peach buds enter the popcorn stage; the last ones well after the host's jacket stage. The long duration of moth emergence affects all of the cyclical events which take place during the growing season — the periodic buildup and decline of moth populations, the duration of the worm broods, etc. As many as 80 days may elapse be- tween the dates on which the first few eggs are laid by early-emerging moths of the overwintering generation and the lay- ing of the first few eggs by a moth of the next generation. The span of each cycle of reproduction and growth — egg to larva to pupa to moth to egg again — is directly affected by weather conditions. Low temperatures retard development and lengthen the reproductive cycles; high temperatures speed up develop- ment and shorten the cycles. Thus, the first spring generation lasts about 80 days, midsummer generations run their course in approximately 30 days. Wind and rainfall also interrupt flight activity, mating, and egg laying. Each cycle therefore does not proceed at an even pace. Such interruptions or slowdowns often create confusion and uncertainty about the tracing of flight activities and the timing of sprays. Stem end of an Elberta peach magnified to show the entrance hole of a fruit moth worm. The entrance was made when the worm was very small. [7] mum, and then an inverse or decline phase. Eggs deposited during a long period of early spring by moths issuing from the wintered cocoons represent the initial stages of the first generation. When these, in turn, develop into moths, the eggs laid bv the latter start the next genera- tion. As the season progresses one gen- eration follows another until at least four, and sometimes five, generations of larvae have developed. The first generation runs its course before the second begins. Reproductive cycles are not interrupted The moth stage of the Oriental fruit moth m Succession of generations The growth stages in development fol- low one another in a regular pattern. However, since different individuals in a population begin a stage on different dates, each growth stage begins or ends for a few individuals on one day, for a few more the next day and so on. The time trend for each growth stage in- cludes a beginning, a buildup to a maxi- A mature worm removed from the flesh of a peach. It is during this larval stage that the Oriental fruit moth causes fruit damaee. Gum-filled exit holes, where worms crawled out of the fruits. but appear discontinuous because the hidden pupal stage intervenes between the larval and moth stages. The pupal stage separates the several moth flight periods and larval growth periods into periodically recurring "broods" or gen- erations. The break between second and third generations, during June or early July, is less pronounced than between earlier generations. Not all the worms of the second brood disappear from the trees before the next brood begins to ap- pear. The remaining broods or genera- tions overlap so much that worms and moths seem to be continuously present though not equally abundant at all times. Since weather conditions also greatly affect the rhythm of the pest's activity, the periods of peak abundance during the first two or three generations of moths and larvae should be determined an- nually for each locality. The duration of each growth stage for the several generations is shown in the table below. Such data provide a broad basis for estimating when to ex- pect the appearance or recurrence of any particular stage in the life cycle of the pest. The variations from generation to generation illustrate how the progress of season affects time required for develop- ment — but there are limitations because the data are applicable only to a par- ticular place (Dinuba) and to a specific year (1945). Duration of Immature and Mature Stages in the Life History of the Oriental Fruit Moth* Stage Incubation period of eggs Min. Mean Max. Feeding period of larvae on peach twigs Min. Mean Max. Feeding period of larvae on peaches. Min. Mean Max. Pupal period — entire cocoon stage . . Min. Mean Max. Life span of female moths Min. Mean Max. Period before females begin to lay- eggs Min. Mean Max. Period of egg laying Min. Mean Max. Total life cycle Mean Over- wintering 4 12 23 4 6 12 3 8 13 Generation First Second Third Fourth days Fifth 4 3 3 3 6 4 3 4 9 5 4 7 15 21 10 13 10 15 Twigs hard 27 16 18 14 8 8 8 23 12 11 13 33 19 18 30 8 8 9 9 14 10 11 14 36 13 14 23 3 4 3 3 14 14 18 16 23 23 29 32 2 2 3 5 5 6 4f 14 13 11 1 1 1 9 8 10 16t 18 13 16 48 32 32 35 13 Twigs hard 15 24 34 * Based on specimen reared in an insectary, Dinuba, Tulare County, 1945. t Records discontinued after November 20. Values of means rounded off to nearest whole number. [9] HOW INFESTATIONS SPREAD The Oriental fruit moth spreads from one orchard to others nearby when the moths fly. The larva cannot creep more than a few feet beyond the base of its host plant. The moth is unable to fly long dis- tances. Marked specimens have been liberated and later recaptured as far as one mile from the point of release, but the flight of moths is probably not the principal means of spreading infestations over great distances. The real problem lies in the transport of the pest in its passive, cocooned stage. Federal and state quarantine regulations, as formerly applied to the fruit moth situation in California, were especially concerned with the transportation of nursery stock from infested areas, ship- ments of worm-infested fruits and used containers, and movements of trucks and railroad cars used for transporting host materials. Mature larvae within boxed fruits leave the fruits and spin cocoons in corners, crevices, or cracks in the containers. Fully developed larvae exit soon after the fruits are handled or disturbed. Less ma- ture larvae continue to feed in the fruits until mature and ready to come out. Thus the worms of diverse ages when the fruit is packed creep from these fruits and gradually accumulate in containers or in structures on which the containers are stacked. Cocoons can be built in the tiniest crevices, and it is easy to overlook them. An extreme case was reported by an eastern investigator who recovered 375 larvae between the wooden strips of one bushel basket and lid. Many of these were so well hidden that no casual in- spection would have located them. Enormous numbers of boxes and bins are transported to and from processing plants every year. Some of these con- tainers may be emptied and re-routed to distant points for use in harvesting a dif- ferent crop. Many of the cocooned larvae may remain hidden in the boxes or bins all winter and emerge the next spring. Two methods for disinfesting durable containers are known. One uses live steam, the other fumigation with a lethal gas, such as methyl bromide. In Cali- fornia, where infestations are widespread, the problem of infested containers is of concern for uninfested as well as infested orchards. Spreading to uninfested orchards. The difficulties of preventing introduction of the fruit moth to uninfested orchards were evident when intrastate quarantine and fumigation operations were carried out by the California State Department of Agriculture during the period 1944- 1947. The sheer magnitude of the task as a large-scale public operation soon out- stripped supplies and manpower even at that stage when infestations in Califor- nia were not as widespread as they are now. A grower today would have a for- midable job of decontaminating all in- coming containers and transport vehicles. Spreading to infested orchards. Growers often wonder whether the effectiveness of their spray programs is seriously af- fected by the escape of substantial num- bers of moths out of containers moved onto or stored on their properties. Re- search on this point is lacking but experi- ence seems to indicate that the cost of ridding containers of the pest exceeds the benefit. The more practical procedure is to destroy the immigrant moths and their progeny with the regular orchard spray program. The "edge effect." Another disturbing as- pect of the spreading of infestation con- cerns the "edge effect" or orchard inter- action. When one infested property is carefully treated and the next one neg- lected, to what extent does the second recontaminate the first? A large amount of research indicates that observable dif- ferences in infestation between treated and untreated plots persist for at least several months after test sprays are ap- plied. Similarly, treated and untreated orchards coexist for reasonably long pe- riods of a growing season without becom- ing equally infested. But if one or two [10] moth flight periods intervene between the dates of final spraying and harvest dates, the marginal rows of a treated orchard adjacent to another, heavily infested or- chard are apt to yield more wormy fruit than its center rows. No information is available to specify how many border rows of trees should be especially treated as a "buffer zone." But it is common experience that the benefit of an annual spray program in one orchard will not be offset drastically within a season by the proximity of an untreated orchard. HOW TO JUDGE INFESTATIONS Moth traps are very useful for determin- ing the time and extent of buildups of this pest. This section of the circular de- scribes how to prepare traps and how to record and interpret moth trap data. Construction and maintenance of moth traps A bait trap for sampling fruit moth popu- lations is a bucket-like container filled with a fermenting or aromatic fluid. Moths attracted to the trap flutter into the liquid and are held by its surface film. If the sides of the container are nearly vertical, the trapped moths are unable to drag themselves out of the liquid. They float on the surface for two or three days until they drown and sink. Select a container holding two to three pints of liquid when filled to within 1 inch of the brim. The suspension, or bail, can be fashioned from light-gauge wire. A three-wire suspension is better than the two-point suspension of the ordinary bucket handle. Twist the upper ends of the three suspending wires tightly to- gether and bend this twisted shank into an evenly rounded hook, about like that of a coat hanger. 1 £ Closeup of the liquid in a bait trap containing eight or nine Oriental fruit moths and very few specimens of other kinds. [ii] No fixed standards exist for trap size, — small moths, millers, flies, lacewings, thus the value of trap records for making etc. Count the Oriental fruit moths float- comparisons or sharing information will ing on the surface, then stir and strain be lost unless traps are made truly com- the liquid in the traps to find additional parable. The rules-of- thumb about seri- drowned specimens. You may pour the ousness of infestation are based on traps contents through a 6-inch kitchen strainer having a diameter of 4?2 inches measured into an empty pail and then back into the across the brim and a depth of 4 inches. original, or you may interchange pails. The bait used was a mixture of the fol- To inspect traps you need a pole, a lowing: strainer, a spare pail, and a record book. Teroinvl acetate 10 ml The P ole is re q uired t0 m and han g p I i 11 traps. Provide a bamboo pole or broom R a ' " ' 4 iu handle with a stout hook made of heavy- w k I g au g e w * re or w ith a 4-inch screwhook. The hook should project at a right angle Terpinyl acetate and suitable emulsi- from the axis of the pole, close to its end. fiers are difficult to buy in small quanti- A V-shaped bend in the hook about 3 ties at local stores. Both of these ingredi- inches out from the pole must open up- ents may be supplied by pesticide dis- ward so that it can be inserted under the tributors on a cost or service basis, usually twisted ends of the trap bail and be dis- with the two ingredients combined in a engaged easily when the trap hook is ready-to-use emulsion. Keep the stock lifted over a branch of the tree. supply of premixed bait — sugar solution If you have difficulties identifying and emulsified terpinyl acetate — cool and Oriental fruit moths in the trap, your in a vented container so that gas evolved Farm Advisor or county officials will can escape. Unused stock mixtures kept assist you. for more than four or five weeks should TT l i i be discarded. How to record moth trap data Hang traps fairly high in the trees, on A record of numbers of moths captured stout laterals, and located so that no in the traps will help you follow the suc- leaves dangle into the liquid. Traps cessive generations of the moth stage, should swing freely, without bumping Traps are inspected daily, or at short in- into heavy branches when trees sway. tervals, and the number of fruit moths Renew the bait in all traps after a strong taken from each trap is recorded. No wind or, in any case, at intervals of about fixed schedule as to the hour of the day 10 days to minimize deviations in bait i s required for servicing the traps because composition. few moths, if any, will be captured by the One trap samples moths in the tree in traps during full daylight hours. Moth which it hangs. It may also attract some counts are averaged for both days and moths from adjacent trees but it becomes traps. For example, if five traps contain much less effective as distance increases. 18, 12, 20, 16, and 9 moths after three Moth activity around any one tree may days, the total is 75 moths in five traps not represent the general level of activity in three days. This averages to 15 moths for the orchard, and it is desirable to op- per trap in three days, or five moths per erate about 10 traps, placed in some day. Moths per trap per day (MTD) is regular pattern throughout a planting of calculated as follows: 10 to 20 acres. Individual traps are easier , . . , n _ A , Tn p , r i- -r .r. • • Moths — traps — days -MID. to rind tor inspections it their spacing is r J regular and linear. For example, a trap When the weather is erratic, inspect could be placed in every fifth tree across and strain traps every day. Abrupt or lengthwise throughout the block. In changes of weather produce sharp ups larger orchards a line of traps may be and downs in the moth counts. If favor- shifted from area to area, as conditions able and unfavorable days have occurred suggest. in the period between trap inspections, Bait traps capture a variety of insects the average count for such a period may [12] be misleading. Most or all of the moths recovered from traps left for several days without attention may have been caught during the only favorable day in the in- terval between inspections. When to operate the traps The most reliable way to trace the course of infestations is to operate traps contin- uously, from blooming to harvest. Dis- continuous trapping operations can lead to confusion because each time traps are installed anew, a variable number of ob- servations are required to reestablish the trend. Since the first two generations are separate, or nearly so, the moth counts show upward and downward trends as each flight period passes — and the traps may be idle during the in-between period. Particular attention is required for the fol- lowing vital periods: 1. Blooming period. The flight of moths from the overwintering generation is expected to begin about March 10. This flight often appears to be a series of scattered flurries because cold, rain, fog, or wind frequently 100 5 Q Q_ < a: x h- o 3 80 60 40 20 interrupt what otherwise would be an evenly moving trend of popula- tion buildup and decline. This pro- longed generation requires at least five weeks of trapping to insure that any delayed upsurge of moths from overwintering larvae will be de- tected. 2. Peach thinning period. The flight of the first-generation moths is expected to begin about May 10 and end ap- proximately 30 days later. 3. Before harvest begins for early clings. The flight of second-genera- tion moths is expected to begin about June 15. This flight overlaps with the next one which follows late in July. Moth counts made during the first pe- riod provide a "sizing-up" of the task ahead; counts made during the second period give a "progress report" on what is being accomplished; and observations made during the third period may be re- garded as the "safety check." Counter- measures applied later than the time when worms begin to attack near-ripe peaches, are essentially salvage operations. MAR APR MAY JUN JUL AUG SEPT Average numbers of moths caught in traps in a cling peach orchard, Kingsburg, Fresno County (Gaume variety, 1955). The curve for March-April (OW) represents moths de- veloped from overwintered larvae, and the four subsequent generations of moths are marked 1 to 4. The heavy bars below the baseline show the periods during which larvae of the first two generations were present in twigs. The tracing of larval development was dis- continued in July because the presence of larvae at all times thereafter made it too difficult to distinguish generations. Extensive control measures were responsible for the decline of the infestation and crop losses were negligible. See text for details. [13 Moth trap records combined for 18 cling peach orchards at Wheatland, Yuba County, 1964. The significance of the heavy bars below the baseline is explained in the graph on page 13. Moth buildup in July and August required control measures before harvest. See text for details. Although it is difficult to know what any one MTD value means at the mo- ment, it is a useful value for comparing moth densities among periods, orchards, or spray programs. A trend usually be- comes apparent when several consecutive MTD values are computed and recorded. The pattern or trend of moth flights through certain critical periods provide a basis for deciding control strategy. Two graphs on pages 13 and 14 illus- trate two very different conditions of in- festation. The first graph (page 13) represents the record of five bait traps operated in one peach orchard which had a serious crop loss during the harvest period of 1954. At the end of that year the orchard was severely infested with overwintering larvae. The carry-over of the heavy in- festations was demonstrated with bait traps during the next spring. The moths trapped during March and April, 1955, came from overwintered worms (OW). The traps were installed on March 19, 1955, and serviced for the first time on March 21, too late to show the actual be- ginning of the moth flight period. The number of moths captured rose rapidly to a high peak, on March 29, and then declined until no more were evident for almost a month (April 21 to May 13). Meanwhile the eggs they had laid, hatched and eventually turned into moths during May. The recurring generations of moths are numbered 1 to 4 on the graph. The serious crop loss during the pre- vious year and high counts of moths dur- ing March and April indicated the need of an all-out control effort. Ultimately this consisted of six applications of DDT, one or two applications for each generation of worms. The curve of moth counts shows how the pest density declined until har- vest date, August 18, The crop loss was held down to less than 0.4 per cent. The other graph (above) shows an opposite trend. The curve is plotted from pooled data obtained in a num- ber of clustered orchards. The season (1964) started with moderate numbers of moths from overwintering worms (OW) but the infestations increased to poten- tially damaging levels before the peak of the peach harvesting period. One spray containing an organic phosphate insecti- cide was applied when first-generation worms began to appear in foliage (first week of April), but it was not sufficient to prevent appreciable buildup during the 14] second and third moth flight periods. Seri- ous consequences were averted by air- craft applications of carbaryl dust before the peaches ripened. Evaluation of trap records The usefulness of trap records depends upon how well they can be translated into practical information about the likelihood of serious crop damage or major expense. There is no infallible way to do this be- cause many variable or unpredictable fac- tors may interfere. Two crude guides have been devised to assist growers in relating moth counts to possibilities of crop dam- age. The "two-ten estimate" is a rule-of -thumb for anticipating spray needs according to moth counts observed during the first (OW) moth flight period. Moth counts converted to daily trap averages (MTD) can be judged according to three intensity levels: • When daily averages are 2 MTD or less, the level of infestation is trivial; spraying is not necessary during this flight period. Check again during the next flight period. • When daily averages range from 2 to 10 MTD, the level of infestation is light; spraying when the first worms appear in twigs may suffice to pre- vent serious buildup during the har- vest period. Check the next flight period. • When daily averages exceed 10 MTD, the infestation ranges from moderate to heavy, according to how high the counts go and how long the high counts persist. At least two sprays should be anticipated, one spray for each of the first two gen- erations of larvae. Counts above 50 MTD for one or several days during this part of the season indicate seri- ous trouble ahead if spraying is not done well. Theoretically, a fertile female moth of the overwintered generation could give rise to more than 15 million females of the fourth generation, most of which would be laying eggs during the peak of peach harvest. If the earliest generation is ap- preciably reduced by a pesticide, so is the likelihood for buildup of a heavy infesta- tion in the remaining three generations. The hazard of crop destruction diminishes appreciably as each generation passes without flaring up, and the significance of numbers of moths caught in traps changes as the season advances toward harvest date. In other words, a maximum count of 10 MTD during March or April may mean possible danger, but two genera- tions later the same value may be re- garded as a fairly safe level. When rapidly growing shoots mature and become woody, some of the worms shift their attacks from twigs to fruits. On heavily infested trees, competition for food results in a "spillover" of larvae from shoots to fruits. Limited evidence also indicates that fruits become more susceptible as they ripen. The extent to which lush shoot growth protects ripen- ing fruit is not known, yet experience has shown that peach orchards can tolerate low-level infestations while maturing an almost worm-free crop. The "Thirty-by-five" estimate: infesta- tions averaging higher than 30 MTD for five days during any 30 day period after May 15 are likely to cause significant amounts of crop damage. This rule-of-thumb attempts to define a tolerance for infestation level in terms of moth counts, as applicable to the sec- ond and subsequent flight periods. The rule has limited value as a guide for spray- ing because it indicates only what a barely acceptable end result should be; it does not specify how to achieve it. No simple statistic or magic number can be pro- posed to describe how low the moth counts must be at any early period to guarantee that infestations will not ex- ceed the tolerance at a later date. If a "substantial" flight of moths is ob- served during the second flight period, and treatment is deferred, the affected orchards will probably require spraying or dusting later, at a time when cultural practices interfere most. Veteran observ- ers tend to emphasize early-season con- trol, and recommend that control be com- pleted, if possible, before mid-June. [15] Indications of time for spraying Communities where Oriental fruit moth is a problem should have information about the activities of its larvae, especially when the first two or three generations of larvae begin to appear and when they begin to decline or leave the foliage. For maximum results, the control meas- ure should be applied in time to affect the largest number of newly hatched worms — as soon as hatching begins and the first few very small worms can be detected in the growing tips of tender shoots. An ef- fective, persistent insecticide applied at the onset of hatching acts against both moths and worms. Toxic residues on leaves and tree framework not only affect moths present at the time of spraying but also those which emerge during the next few days. The residues also destroy worms hatching after applications. How long the residue remains effective de- pends on kind of material, amount of de- posit, temperature, rainfall, etc. But even the best applied spray leaves survivors because it cannot cover everything and its residue loses its killing power before some of the moths emerge. Twig sampling. The sampling of peach twigs to detect fruit moth infestation is an essential part of the information needed to determine the best time for control. An experienced person must patiently and carefully search for the first signs of at- tack on shoots by the worms of an oncom- ing generation. Success depends on know- ing approximately when to expect the at- tack, where to start looking, and how to detect twig damage in the early stage before wilting occurs. The observer also must be able to distinguish between old, mature worms of an outgoing brood and the very small worms of the oncoming brood. Experienced growers, farm advi- sors, and technical fieldmen are usuallv best qualified to secure and interpret such twig-sampling data. When the timing is established by a competent person it is broadly applicable to stone fruit orchards within a large community. Moth counts. It is sometimes possible to rely on moth counts to find the best time for spraying. For example, the feeding periods of the first two generations of fruit moth worms are indicated by the lengths of the horizontal bars drawn be- low the baselines of the graphs on pages 13 and 14. In the first graph, the peaks of the moth flights (OW, 1, 2) coincided closely enough with the start of egg hatch- ing to indicate the time for spraying (March, May and June). In this instance the periods of maximal moth flight ac- tivity were clear. In another instance (graph, page 14), the early-season moth flights were irregularly interrupted and extended by unfavorable weather. The hatching of first-generation eggs began long after the highest moth counts (OW) were recorded. Also, the flight period of first generation moths (1) had no obvious peak. Therefore it was necessary to de- termine the date to spray for this genera- tion by searching for newly hatched worms in the tips of twigs. Preharvest evaluation. The payoff on the investment for control should become ap- parent when the third flight of moths be- gins. If the moth counts remain well be- low the tolerance level throughout the period from June 15 to July 15, the vari- eties yet to ripen are not apt to require further treatment. Continued surveillance with moth traps is strongly recommended. On the other hand, when moth counts approach the tolerance level during the third flight period, the affected orchard should be treated immediately. The best time for treating larvae of the third gen- eration is likely to be near the end of June. Peach crops accumulate worm damage until harvest date. A recent study of peach damage by fruit moth showed that a part of the damage occurred 15 days or more before the harvest date. The varieties of peaches which ripened during July sus- tained much of their damage during the period of late June to early July. But the varieties which ripened in August also acquired a significant amount of damage during the same period, despite the fact that they were treated later. Our tests showed that 10 per cent carbaryl dust rapidlv depressed moth counts and held them down for a considerable period; yet later ripening varieties with heavy infesta- tions, which were not treated until shortly before harvest, still showed crop damage, presumably acquired before dusting. [16 THE FRUIT MOTH AND THE PEACH TWIG BORER The prevalence of the peach twig borer in California orchards complicates the selection of spray materials and the tim- ing of sprays. Although the fruit moth and the twig borer have several habits in common, especially the mining of shoot tips, their life cycles do not run concur- rently. A population of the fruit moth over- winters as full-grown larvae. The latter transform into moths about the time peach trees are in full bloom. The moths, or reproductive individuals, appear in in- creasing numbers during the petal fall pe- riod but the eggs which they lay do not begin to hatch until somewhat later. The best timing for the first insecticide appli- cation occurs during the early jacket pe- riod of fruit development. Winter sprays, as sometimes applied to control the twig borer, are relativelv ineffective against wintering larvae of the fruit moth. Peach twig borers, on the other hand, overwinter as very small, immature larvae hidden within burrows under the soft bark of their host trees. When peach trees begin to bloom the tiny larvae leave their burrows and feed on swollen buds and undeveloped shoots. Later on they bore into the tips of longer shoots. Some twig borer larvae grow almost to maturity be- fore the first young larvae of the fruit moth appear. The usual time to spray for twig borer is just before blooming begins Worms of the Oriental fruit moth and the peach twig borer can be dis- tinguished according to color. The worms of the Oriental fruit moth are cream, flesh-colored, or faintly pink; those of the peach twig borer are reddish brown or chocolate, with narrow, lighter-colored bands between the body sections. (pink bud) or as soon as petal drop is completed. When serious infestations of both pests affect the same orchard — and no earlier spray has been applied to control the twig borer — then two post-bloom sprays are advisable, a petal fall spray for twig borer and a second or cover spray for fruit moth. However, if the two pests are not equally abundant, a one-spray compro- mise can be made according to which pest is dominant. The date for spraying can be advanced closer to petal fall to favor twig borer control, or delayed until fruit moth eggs begin to hatch to favor fruit moth control. The growth stages of the two pests progress at unequal rates and the be- ginning of their second worm broods (i.e., technically first generation twig borer lar- vae, second generation fruit moth larvae) more nearly coincide. A spray applied on or close to May 25 is apt to have a near- maximal effect on both pests. ACKNOWLEDGMENTS The following members of the University of California Agricultural Extension Serv- ice have assisted in field research when serious outbreaks occurred in their counties: J. H. Foot and J. H. LaRue (Tulare), L. C. Brown (Kings), John Quail and C. A. Ferris (Fresno), N. W. Ross (Stanislaus), G. R. Post and B. W. Ramsaur (Sutter) and A. H. Retan (Butte). Satoru Togashi, California Packing Corporation, Wheatland, has done extensive plot work with pesticides and moth traps. He has been most generous in sharing his data and experience. [17] PESTICIDES Inasmuch as pesticide recommendations change periodically because of new research and modifications in registration, consult the most recent Pest Control Guide (Peaches and Nectarines) for the latest controls. This guide is published by the University of California Agricultural Experi- ment Station and Extension Service. Co-operative Extension work in Agriculture and Home Economics, College of Agriculture, University of California, anil United States Department of Agriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914. George 15. Alcorn, Director, California Agricultural txlension Service. 12Jm-8,'66(G2192)J.F. [18]