UNIVERSITY OF CALIFORNIA Agricultural Experiment Station COLLEGE OF AGRICULTURE ^ENJ. IDE WHEELER, Pres.dent THOMAS FORSYTH HUNT, DCAN AND DIRECTOR BERKELEY CIRCULAR No. 101 (June, 1913) CODLING MOTH CONTROL IN THE SACRAMENTO VALLEY BY C. W. WOODWORTH The investigation by this Station of the problem of preventing wormy apples or pears has been condncted chiefly in the great apple section of this state, the Pajaro Valley. Dnring the summer of 1911 Mr. L. J. Nickels, an assistant in the Entomological Department was given opportunity, through the cooperation of Mr. H. P. Stabler, Horticultural Commissioner of Sutter County, to compare the life history of the insect in that region. A detailed account of this investi- gation is soon to be published. LIFE HISTORY In striking contrast with the conditions prevailing in the Pajaro Valley the moths appear early in spring and are ready to begin to laj^ their eggs before the petals have fallen from the blossoms. Egg laying is concluded in about a month. Fig. 1. — Newly -hatched codling moth larva crawling between the stamens in the blossom cup of apple, also young woolly aphis. Fig. 2. — Surface feeding by young codling moth larvae, a, b, c, successive feedings. Fig. 3. — Section through the same spot as figure 2. The eggs are flat, transparent, cemented fast to the surface of the leaves or fruit and about the size of a pin head. They are so incon- spicuous as to be difficult to find. Eggs hatch in about 81/2 days and the young larvae are abundant in the apples by the time they are as large as peas. The young worm first makes a burrow, not eating the fruit, but biting off bits, which it uses in making a canopy over the entrance, binding these fragments together with silk. After establish- ing itself within the fruit the worm begins to feed both within the burrow and on the surface, and continues to live just beneath the skin for several days, finally burrowing deep into the fruit. In all a little less than a month (average 27 days) is spent within the fruit. Upon leaving the fruit the worm proceeds to spin a tough silken cocoon in some crevice and remains another month within this protection chang- ing into a pupa and finally emerging as a moth, completing a full generation by the middle or latter part of July, some individuals developing more rapidly and others taking considerably longer. A second generation occupies August and September and a few of the more precocious are able to produce a third generation in the fall. Usually the worms of the second generation go into hibernation as soon as they have spun their cocoons and do not transform till the follow- ing spring. FRUIT AFFECTED Apples. — Most of the apples grown in the Sacramento Valley are early fruit which is ready to harvest early enough to escape the attack of the second brood of worms. Where nothing is done to protect the fruit the worms injure but two-thirds of the crop. If the orchard were isolated and all fruit removed at this time, the second generation might be largely annihilated by starvation. Pears, are very much more largely grown in the Sacramento Valley than is the apple and is not usually seriously affected by the first brood of worms (less than 10 per cent) but if not controlled the worms of the second generation injure a third of the crop. The usual method of harvesting pears removes the larger proportion of the worms of this second generation from the orchard, hence the relatively small injury from the first generation of the following spring. THEORY OP CONTROL The gathering and destruction of fallen fruit was at one time required by law in California. The placing of bands made of old grain sacks around the trunk and examining them once a week or once in two weeks was found to enable the grower to destroy more of the worms than by gathering the fruit and was the chief depend- ence in this state a score of years ago. A parasitic wasp was imported from Spain which feeds on the insect but this proved of no practical value. The use of arsenical poisons has coma to be the sole method for the control of this insect. By their use the insects are killed before instead of after the danger is done and the loss can be reduced to the neighborhood of one per cent and sometimes the destruction seems to be complete. At first it was thought that the poison could not affect an insect like this that bores deep into the fruit. When experi- ments proved that the poisons did protect the crop the general belief changed to the idea that they got the poison in the process of burrow- ing through the skin. The fact noted above that they do not swallow the tissue removed in this process suggests that the subsequent surface feeding is the fatal operation. The fact was early observed that in some regions the worm enters the fruit chiefly at the blossom end, giving rise to the erroneous idea that the eggs were laid at that point. It is a very general belief that poison must be deposited within the cup to prevent the entrance of the worms, and in most varieties of apples this can only be done during the fortnight following the dropping of the petals. In the Pajaro valley it was observed that the great majority enter the fruit else- where and in Sutter county only a third of the worms entered at this place. Furthermore, it was noticed that spraying was completely effective in the Pajaro valley when applied long after the calyx is closed and in the Sacramento valley good results followed when only two or three per cent of the cups showed an appreciable amount of the spray. In both of these cases the decrease of those entering the blossom end was practically as great as of those entering on the side. It will thus be seen that we do not know enough of the facts to explain the reasons for the efficiency of the poison. METHOD OF CONTROL All who have investigated the subject agree that the poison must be applied before the worms enter the fruit and that a thorough application is necessary for the best results. Both the life history and observations of the results of practical spraying work indicate that the time for the first application in that valley is as soon as possible after the petals fall. 4 In the case of pears or fall apples, unless this first spraying has been very thorough, the second brood will also need attention the latter part of July or early in August. The placing of bands of sacking about a few of the trees is advised as a means of keeping track of the appearance of the second crop. These should be examined about the 1st and 15th of July aud August. One thorough spraying for summer apples and one or two for fall apples and pears will completely control the codling moth in the Sacramento Valley. AMOUNT TO USE For a single medium-sized tree: Lead Arsenate i/^ pint Water 5 gallons For Orchards use: Lead Arsenate 3-6 lbs. Water 100 gallons This is enough for about a quarter of an acre of average sized trees. Instead of Lead Arsenate one can substitute Zinc Arsenite, using only one-third as much (1-2 lbs. for 100 gallons) or Paris green, using a quarter as much as of the lead (%-% lbs. to 100 gal- lons), in the latter case it is customary to add about three times as much lime. This serves two purposes, holding the arsenical on the tree and marking the tree so that one can be sure of the thoroughness of the application.