I9" BETTER FRUIT p«ge 27 



SOME INSECTS AND MITES ATTACKING THE PEACH 



BY GEORGE P. WELDON, EXPERIMENT STATION, FORT COLLINS, COLORADO 



THE novice in the business of grow- 

 ing peaches in Colorado very often 

 begins with a mistaken notion that 

 peach trees require no spraj'ing. That 

 notion has probably grown out of the 

 fact that in the early history of orchard- 

 ing in the state spraying for the control 

 of insect pests was confined almost 

 entirely to apples. While the spraying 

 of peach trees may not be necessary 

 every season there are times when cer- 

 tain sprays are necessary in order that 

 destructive pests may be controlled. One 

 who hopes to make a success growing 

 high grade fruit must resort to spraying 

 whenever the prevalence of some insect 

 pest demands it. It would not be wise 

 to lay down set rules for the spraying 

 of peaches, for there are too many fac- 

 tors that may bring about a marked 

 increase or decrease in the numbers of 

 certain pests occurring from season to 

 season. For example, last spring a very 

 severe infestation of the common green 

 peach aphis in the peach growing sec- 

 tions of Colorado made it necessary that 

 stringent methods of spraying be adopted. 

 The previous spring the occurrence of 

 this pest was very general, but it was 

 not abundant enough in most orchards 

 so that it was necessary to spray for its 

 control. Often a dormant spray of lime 

 and sulphur or soluble oil is beneficial in 

 orchards where certain pests may be 

 spending the winter. Too much, how- 

 ever, should not be expected of dormant 

 sprays, and while there are insects that 

 they may control very efifectively there 

 are others that will be controlled but 

 partially or not at all. Very often the 

 orchardist who uses a lime and sulphur 

 spray seems to lose sight of this fact, 

 and because the spray does not meet 



LARVAE IN BURROW 



with his expectations in controlling some 

 certain, pest he condemns it for all of 

 them. As a matter of fact he probably 

 was paid for its use in the destruction 

 of some other pest. 



One of the most common enemies of 

 the peach in the United States is the 

 twig-borer or "bud worm," as it is some- 

 times called. Its occurrence has been 

 reported from most of the peach grow- 

 ing states of tlie Union, both in the East 

 and West. In Colorado it has been 

 known for a number of years, and while 



it is not a seriously injurious pest every 

 season there are seasons when it becomes 

 exceedingly destructive, and is respon- 

 sible for a great financial loss to those 

 peach growers who do not adopt proper 

 methods of control. 



The adult of the twig-borer is a tiny, 

 dark gray moth. It is an Old World 

 species, supposed to have come to us 

 with the peach from Western Asia, and 

 has been known in the United States 

 since 1860. The twig-borer is principally 

 an enemy of the peach, and usually we 

 hear of it in connection with its damage 

 to this fruit. It may be found, however, 

 on all stone-fruit trees, but shows a 

 decided preference for the peach. In 

 Bulletin 80 of the United States Depart- 

 ment of Agriculture Dr. Marlatt men- 

 tions the pear among its list of food 

 plants. The writer has never noted the 

 attack of this insect upon other than 

 stone-fruit trees. Its occurrence on the 

 pear or other pome fruits is probably 

 rare, and might be compared to the 

 occurrence of the codling moth, which is 

 almost exclusively an enemy of the pome 

 fruits, in plums, peaches or other stone 

 fruits. While cases of codling moth 

 infesting stone fruits in any numbers are 

 rare they were found the past season 

 so plentiful in Burbank plums of a cer- 

 tain orchard that they were really doing 

 considerable damage. The twig-borer, 

 during a season of abundance, might 

 occasionally modifj^ its habits to the 

 extent of an occasional attack upon pome 

 fruits, as the codling moth in a season 

 of abundance may modify its habits and 

 occasionally attack stone fruits. 



The larvae, as is shown in Figure 1. 

 hibernate in little silk-lined chambers 

 constructed within the bark and very 

 close to its surface. Mr. Warren T. 

 Clarke, in California Experiment Sta- 

 tion Bulletin 144, states that "in the 

 majority of cases they are found just 

 beneath a thin layer of the greener cells, 

 just below the brown bark, while the 

 greater part of the burrows is in the 

 yellowish portion of the cambium." He 

 also states in connection with the winter 

 burrow within the bark that "the posi- 

 tion generally chosen on the tree for the 

 purpose is the crotch formed where the 

 new wood joins that of the previous year, 

 though older crotches are occasionally 

 selected." In Colorado I have found 

 them almost entirely in the older 

 crotches, and always, when found there, 

 they have been in the brown portion of 

 the bark, just as close to its surface as 

 the hibernacula could be constructed. 

 Occasionally the hibernating cells con- 

 taining larvae have been found under- 

 neath buds on the new growth of peach 

 trees. Their occurrence in this location 

 does not seem to be at all general. 



While hibernating the larvae vary 

 somewhat in size, but are all very small, 

 and their detection is somewhat difficult, 

 except when very close observations are 

 made. The presence of the larvae them- 

 selves during the hibernating period 

 could scarcely be detected were it not 



for the fact that they construct at the 

 entrance to their burrows tiny silken 

 tubes covered on the outside with bits 

 of bark, which were chewed ofif by the 

 larvae while excavating the hibernacula. 

 These little tubes are shown in the crotch 

 of a tree in Figure 3, and again one is 

 shown at the entrance to a burrow con- 

 taining larvae in Figure 2. The larval 

 cell is also lined with silk, the silken 

 tube being merely a continuation of this 

 cell lining. Throughout the winter 

 months the hibernating larvae remain 

 inactive within this cell. Apparently no 

 feeding is done after the time that they 

 construct the cells until they leave in the 



TUBE ENTRANCES TO BURROWS 



spring, consequently no growth takes 

 place during that time. A hibernating 

 larva, magnified twenty-six times, is 

 shown in Figure 1. These larvae are 

 exceedingly well protected in their hiber- 

 nacula, and Mr. Warren T. Clarke's 

 experiments in California show that they 

 are almost impenetrable to even an oil 

 spray during the winter season. 



In the spring of the year, about the 

 time the peach trees bloom, the larvae 

 leave their winter quarters and eat into 

 the tips of the twigs, either beginning 

 their work at the extremities or a short 

 distance below, sometimes hollowing 

 them out for usually a distance of less 

 than an inch from where the twig was 

 entered, leaving a mere shell or hollow 

 cylinder of the portion in which they 

 have fed. Again, they may merely 

 goiige out the tip of a twig on one side, 

 entering in as far as the pith and then 

 leaving for some other twig. Thus thej' 

 go from twig to twig, feeding first in one 

 and then in another, until often the tips 

 of a great many branches will be killed 

 back, thereby checking their growth and 

 more or less injuring the tree. The 

 detection of their work is no difficult 

 matter a short time after they begin 

 feeding, for the leaves of affected twigs 

 soon wilt and later dry up from the 

 injury done to them. 



The injury the first brood larvae do 

 to twigs, while sometimes alarming, i'; 

 not usually to be compared with the 

 injury to the fruit from the second and 



