UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION CIRCULAR No. 224 December, 1920 CONTROL OF THE BROWN APRICOT SCALE AND THE ITALIAN PEAR SCALE ON DECIDUOUS FRUIT TREES By E. O. ESSIG The control of the brown apricot scale and the Italian pear scale has been so thoroughly worked out in practice that it seems advis- able to make the information serviceable to many fruit growers who are not familiar with it. This can best be done by describing first the characteristics of the two insects separately and then discussing the control measures for both together. THE BROWN APRICOT SCALEi The brown apricot scale is a soft, unarmored insect in which the outside body wall gradually hardens until maturity, when it forms a protecting, nearly hemispherical shell or egg-sac under which are produced hundreds of small, oval, white eggs. Upon hatching, in early summer, the young insects crawl from beneath the old shell and settle upon the leaves and twigs of the current year's growth. They grow slowly and in the autumn large numbers perish with the falling leaves, but others move to swell the numbers already on the twigs, where they remain through the winter as small, elongated, brown, immature individuals. With the warm spring and early sum- mer days they grow rapidly and by July and August are mature and produce eggs, the mature females dying soon afterwards. During growth the young scales excrete quantities of honey dew which drops on the leaves, limbs, and fruit of the trees and upon which the black smut fungus thrives. In this way the scale insect is directly responsible for smutting, the most serious injury caused by this insect. The males are very minute, winged individuals which do not feed, so that they are not injurious. They mate with the females when the latter are only about half grown. There is but one generation of 1 Leoanlum corni Bouche. It is also known as the European fruit lecanium. 2 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION the insect a year. The females are often attacked in great numbers by a small hymenopterous parasite, Comys fasm Howard. The larvae of this parasite live within the bodies of the scales, causing them to assume a very dark color and eventually to dry up and die. The work of Comiys fusca Howard is uncertain and sporadic, so that it can be considered merely as an adjunct in the control of the scale though sometimes of importance. The brown apricot scale is a very general feeder attacking prac- tically all kinds of deciduous fruit trees, vines, and many wild and ornamental trees and shrubs. In California it may be found through- out the length and breadth of the state, but flourishes best in the warmer valleys, along the coast, and in the interior. THE ITALIAN PEAR SCALE2 In contrast to the brown apricot scale, the Italian pear scale is an armored scale in which the small, oval, dark red body is protected by an elongated or nearly circular tough gray shell or scale which averages about one-sixteenth of an inch in diameter. The scales of the males are minute, long, narrow, pure white, delicate structures with a dorsal median longitudinal furrow. They average about one thirty-second of an inch in length. The males may or may not be present in large numbers among the females. They are very small winged individuals much like those of the brown apricot scale and are of no consequence except in fertilizing the females. The young hatch from small, oval eggs deposited beneath the shell of the female. For some days they move about freely; with the first moult, the spinning of the shell begins, and with subsequent growth the legs disappear and the insect becomes fixed to the bark, unable to move farther. Breeding continues throughout the spring and summer, there being several overlapping generations a year. This scale feeds only on the bark of the trunk and limbs of the trees and hides under moss or lichens wherever an opportunity is afforded. It excretes no honey dew, and consequently smutting is not associated with its attacks. In feeding, however, it causes pits or depressions in the larger limbs, which may eventually crack or become dead sunken areas, especially on old trees where the insect has occurred for many succeeding years. The Italian pear scale is not widely distributed as an orchard pest, being largely confined as such to the Santa Clara Valley and adjacent territory, although it occurs in many other parts of the state. 2 Epidiaspis piricola Del Guercio. CIRCULAR 224 CONTROL OF SCALE ON DECIDUOUS FRUIT TREES 3 Fig. 1. — The brown apricot scale, Lecanium corni Bouche, on prune. Mature females. 4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The chief host plants are apple, prune, pear, plum, peach, currant, and Christmas berry. The apple, prune, and pear are the plants most seriously attacked. The chief natural enemy is the two-stabbed ladybird beetle, 3 but it is never present in sufficient numbers to cope successfully with the scale. SPRAYS4 The sprays most effective in the control of these two scale insects are distillate emulsions, crude oil emulsions, and miscible oils. For the brown apricot scale alone, any of these, if properly prepared and applied, will give excellent results. The Italian pear scale, however, is more resistant and requires heavier and more numerous applications of distillate emulsions and miscible oils. This scale yields most readily to the crude oil emulsions, which are far superior to commercial lime- sulphur for this purpose. Many growers realize the difficulty of securing proper materials for homemade emulsions as well as the variability of the homemade mixtures even under the best conditions. They prefer to buy manu- factured products, especially when only small quantities are needed. The commercial emulsions and miscible oils are no more effective than a good homemade preparation and are only of interest as a matter of convenience. These preparations are on the market in great variety. Many are sold under trade names. Practically all grades of petroleum distillates, as well as crude petroleum, are obtainable in a form ready for use after simple dilution with water. If these ready- made preparations are to be used, it is important to purchase only from reliable and well-known manufacturers or dealers. DISTILLATE EMULSIONS Distillate emulsions may be prepared at home or purchased as ready-made commercial products. They are made from fairly heavy distillates emulsified with soap and caustic soda. A satisfactory 3 Chilocorus bivulnerus Mulsant. 4 The writer has purposely avoided referring to any specific brand of pro- prietary sprays. Orchardists may secure such information from the various local and state horticultural officials and from entomologists and farm advisors. The writer is indebted to Mr. Geo. P. Gray, chief of the Division of Chemistry, State Department of Agriculture, Sacramento, California, for much of the infor- mation relative to the composition and preparation of the sprays discussed in this paper. CIRCULAR 224 CONTROL OF SCALE ON DECIDUOUS FRUIT TREES )' ;.*■* i'-Y % i£'% rtt Fig. 2. — The Italian pear scale, Epidiaspis piricola DelGuercio, on prune and cherry. UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION preparation often made and used by orchardists is prepared accord- ing to the following formula: Distillate (27°-28° Baume) 10 gallons Caustic soda 6 pounds Liquid soap (or hard soap 12 pounds) .... 2 gallons Water to make 200 gallons Directions: Fill spray tank nearly full with water and start agitator. Add liquid soap or hard soap and caustic soda previously dissolved in small quantities of water. When thoroughly mixed add the distillate. This mixture, as well as all the oil sprays, should be constantly agitated during application. The caustic soda not only aids in emulsifying the oils, but assists materially in killing the moss on the trees. If a commercial mixture is used, care should be taken to follow the directions on the con- tainer ; in case proper results are not obtained, the local Count}^ Horti- cultural Commissioner or Farm Advisor should be consulted. The use of proprietary sprays of unknown composition is inadvisable. MISCIBLE OILS Miscible oils are usually fairly heavy oils in which a cresol soap is used as an emulsifying agent. Many of them are proprietary insecti- cides. They require more dilution than the distillate emulsions. They mix with water readily and, if used in proper proportions, are very satisfactory. The reasons for some poor results have been traced to recommendations of dealers who advise solutions entirely too weak to kill the insects. CRUDE OIL EMULSIONS Crude oil emulsions are made preferably from natural crude oil coming directly from the wells. A natural crude petroleum, testing about 23° Baume, is preferred as it contains some of the lighter and more penetrating oils. Heavier crude oils have also given satisfactory results, even those testing 18° and lower. Formula • Water 175 gallons Liquid soap 3 gallons Natural crude petroleum (21 °-24° Baume) 25 gallons Directions: Partly fill the spray tank with water, add the liquid soap, agitate thoroughly for one minute, add crude oil and continue the agitation while running in the remainder of the water. If liquid soap cannot be obtained, use 20 pounds of fish-oil soap dissolved in Circular 224 CONTROL OF SCALE ON DECIDUOUS FRUIT TREES 10 gallons of boiling water to which 3 pounds of caustic soda or lye have been added. To kill moss or lichens on fruit trees add 5 pounds of caustic soda or lye to the formula. During the spraying operations, this emulsion should be thoroughly agitated and great care taken to wet all of the twigs. From 8 to 10 gallons should be used on a tree. There are a number of good commercial crude oil emulsions upon the market. Some of them are made from the natural crude oil, as Fig. 3. — The Italian pear scale, Epidiaspis piricola DelGuereio. Masses and individual female scales. are the homemade mixtures, but emulsification is obtained by secret artificial processes which render the products stable. While crude oil emulsion sprays are annoying to the sprayers because of their heavy, sticky properties, they are the most effective and thorough of all the oil sprays. For killing brown apricot scale they are no better than the distillate emulsions and miscible oils, but for the Italian pear scale, for moss, and for the eggs of the red spider, they are far superior. Injury may occur with crude oils which are not properly mixed or which are composed of poor materials. If there is a quantity of free crude oil on top of the material in the spray tank more soap or caustic soda should be used ; if a heavy scum or residue remains in the tank, relief may be obtained by thinning down the 8 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION crude oil with distillate or kerosene. When crude oil is thoroughly applied, it sometimes penetrates the fruit buds to a considerable extent. Some of these may be injured and even killed, but most of the buds are not injured. Buds may be killed also by applying the free oil or residue referred to above. All these oil sprays and particularly the crude oil emulsions hasten the blooming period of the trees from one to three weeks. Crude oil emulsion has also partially controlled the brown rot fungus 5 which attacks apricot and prune trees in the Santa Clara Valley. The crude oil emulsions originated in the Santa Clara Valley and are rarely found elsewhere, though they have been in use there for the past five or six years. Through the manufacturers, however, their sale is being pushed in other parts of California and in many other states, and their worth is gradually becoming known and appreciated. The brown apricot scale is effectually controlled by applications of crude oil emulsions used for the Italian pear scale, but the latter cannot be killed by the ordinary applications of distillate emulsions and miscible oils unless thorough and repeated treatments are given. APPLICATION OF SPRAYS Orchardists have much to learn regarding the application of sprays, particularly as to the best kind of nozzle. In most cases where poor nozzles are used, the work is done by hired help generally not conversant with the best types of spraying equipment. The use of the single Bordeaux nozzle on an extension rod is common in many parts of the state. As an advance step over this we occasionally find one and sometimes two good, large cyclone nozzles on a rod. The use of a rod thus equipped considerably lessens the time consumed in the application. The advent of the spray gun is a very important step in spraying operations. The chief advantages of the spray gun are: It greatly reduces the weight to be carried by the operator and makes the work of spraying less objectionable. By reason of its light weight it can be more quickly operated. It affords an adjustable spray for all kinds of work. It is easily and quickly cut off when going from tree to tree. Any stoppage of the nozzle can be dislodged by a slight adjust- ment. It throws a greater volume of material, practically doubling the efficiency of each operator handling a line of hose, thereby saving time and labor. 5 Sclerotinia cinerea (Bon.) Wor. ; previously known as Sclerotinia fructigena (Pers.) Sch. Synonymy by Professor W. T. Home. CIRCULAR 224 CONTROL OF SCALE ON DECIDUOUS FRUIT TREES Fig. 4. — Portion of a limb from pear tree showing deformation due to the continued work of the Italian pear scale, Epidiaspis piricola DelGuercio. 10 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION There are many tj^pes of spray guns. In making a purchase the capacity of the spraying machine must be taken into account, for this will determine whether a gun of small or large throwing capacity should be used, or whether one or two should be operated on the machine. A pressure of at least 200 pounds should be maintained at all times. If the machine will not carry this with one gun, spray rods must be resorted to in order to get the best results. It is true that in the beginning one is likely to use more material with a spray gun, but the ease of operation and saving in time and labor much more than offset this objection. The value of the spray gun for many kinds of spraying work has been proved and its popu- larity is fully warranted. It is particularly valuable for the control of the brown apricot scale, which is usually located on the underside of the twigs of the current year's growth where it is readily hit; and also for the control of the Italian pear scale located upon the trunks and larger limbs where a thorough drenching with a strong, coarse spray is necessary. In spraying for the brown apricot scale, care must be taken to cover all of the tips of the small twigs around the edges and tops of the trees where the young insects are located upon the new growth. TIME TO SPRAY Both the brown apricot scale and the Italian pear scale can be controlled best by spraying between December 15 and February 15. During that time the trees are absolutely dormant and safe from spray injury. Application may be made as late as the starting of the buds, but great care must be exercised in late spraying to avoid injuring the blossoms. While injury does not always result from applications made when the trees are in full bloom, applications are dangerous at this time and the spraying should be finished before the danger point arrives. DANGERS IN USING OIL SPRAYS Under ordinary field conditions in California there is little danger in the use of oil sprays, but it is advisable to call attention to a few important points which should not be lost sight of by orchardists. 1. Do not use improper mixtures. If the emulsions of crude oils fail to mix readily with water, and much free oil rises to the surface, or a heavy residue remains after the spray tank has been emptied, suspend operations and consult spray manufacturers, local County CIRCULAR 224 CONTROL OF SCALE ON DECIDUOUS FRUIT TREES 11 Horticultural Commissioner or Farm Advisor as to proper procedure in remedying the product or in securing a reliable new one. 2. Do not apply oil sprays except when the trees are dormant. As already pointed out, injury may result from applying sprays when the buds begin to open in the spring due to the penetration of the sprays into the tender tissues of the buds. Injury may also occur in the fall if spraying is begun too earty, as well as in the spring if done too late,. The trees are most resistant to spray injury from Fig. 5. — Two common types of spray guns used in modern spraying operations. December 15 to February 15 when the buds are thoroughly protected by the closely adhering bud scales. Oil sprays have frequently been applied without apparent injury when the trees are in full bloom, but such a practice is attended with great danger and the possibility of losing the entire crop. 3. Do not spray when the trees are in need of water. During late dry seasons much injury may result in using oil sprays if the trees need water. The use of oils, and in fact of all other sprays, should be delayed until after rain or irrigation. Also avoid spraying after a continued spell of dry winds, for these so deplete the moisture in the bark of the trees as to permit penetration of the sprays from which severe injury to the bark and buds may result.