ORCHARD INSECTS OF THE PACIFIC NORTHWEST 53 



and the infestation becomes serious, a special application of nicotine 

 sulfate may be made at any time it is needed, adding to it 2 or 3 

 pounds of soap in solution or 1 pound of casein spreader to 100 gallons. 



Red Spiders 



Prune and plum trees are often seriously affected by red spiders. 

 The foliage is bronzed and defoliation may occur in nonirrigated 

 orchards, frequently accompanied by the dropping of some of the 

 fruit. Injury by the mites may prevent the fruit buds from forming, 

 or at least may weaken them, causing a small crop or small fruit the 

 following year. This injury is often much more serious than is ap- 

 parent. All of the three species discussed on page 16 occur on these 

 trees. 



CONTROL 



Control is similar to that on apple and pear trees (p. 19). If it is 

 necessary to use sulfur sprays to control brown rot, special applica- 

 tions for red spiders should not be necessary. Summer sprays of 

 oil must be applied before July for the best results. Later applica- 

 tions, besides being less effective, cause the bloom on the fruit to 

 become spotted, and this detracts from its market value. Sulfur 

 sprays do not have this objectionable feature; and if control has not 

 been attained by the 1st of July, sulfur sprays or dusts should be used. 



Rust Mite 



The rust mite (Phyllocoptes schlechtendali Nal.) causes prune leaves 

 to curl longitudinally and become russeted or silvered. The fruit 

 may also be russeted. Control is the same on prune trees as on apple 

 and pear trees (p. 22). 



Peach Borer 



Peach borers are very serious pests of prune and peach trees, as 

 well as of apricots and plums and occasionally cherries. The injury 

 occurs chiefly in the crown and roots of the trees, where the borers 

 tunnel beneath the surface, feeding on the inner or growing layer of 

 bark. Young trees may be completely girdled and killed (fig. 61), 

 and older trees are frequently so weakened that they become subject 

 to other insect pests or to diseases. The presence of borers in the 

 trees is often first indicated by a quantity of gum at the base of the 

 trunk, mixed with dirt and frass. Poor condition of the trees may 

 also indicate the presence of the borers. Trees should be examined 

 periodically for borers, especially if they are not making good growth 

 or do not appear to be thrifty. The borers are most commonly 

 found in the region west of the Cascade Mountains, but sometimes 

 become injurious elsewhere. 



LIFE HISTORY 



The peach borer (Sanninoidea exitiosa (Say)) and the western 

 variety of the same species (S. exitiosa opalescens (Hy. Edw.)), for- 

 merly considered a distinct species, are both found in the Pacific 

 Northwest. The adult is a steel-blue moth with a wing expanse of 



