2 CIRCTJLAB 17 5, U. S. DEPARTMENT OF AGRICULTURE 



operator often blind him temporarily, and he fails to cover thor- 

 oughly all parts of a tree. Lime sulphur, at the usual strength for 

 dormant trees, has little effect on the eggs of the red spiders, of tree 

 hoppers, or of the fruit-tree leaf roller (Archips argyrospila Walk.), 

 or on either the eggs or newly hatched young of aphids. If used in 

 the spring, after the leaves are partly out, it sometimes causes a 

 severe dropping of the fruit buds. Its cost is high where it has to 

 be shipped to a distance. 



The oil sprays are more concentrated, and are cheaper and more 

 easily handled than lime sulphur. They are not so caustic, and they 

 allow the operator to see what he is doing at all times. If used after 

 the buds have started to open, they are more apt to cause injury 

 than the lime sulphur, and they should therefore be used before the 

 buds open. If used at the proper strength, oil sprays control the 

 San Jose scale very effectively, and they also result in a very good 

 control of tree hoppers, red spiders, and aphids. Oil sprays must 

 be used for the eggs of the fruit-tree leaf roller. They are not very 

 effective against the peach twig borer {Anarsio, Jineatella Zell.). and 

 are less effective than lime sulphur against the pear-leaf blister mite 

 (Eriophyes pyri Pgst.). 



The danger of injury to dormant trees from oil sprays is very 

 slight. Trees in this condition have been commonly sprayed in the 

 Pacific Xorthwest for a number of years, with no apparent ill effects. 

 Even where an improperly prepared emulsion was used, which con- 

 tained some free oil, the injury to dormant apple trees was of little 

 consequence. Dormant prune trees have sometimes been killed, how- 

 ever, by applications of oil sprays containing free oil. Oil sprays 

 have been used for 4 or 5 years in the Spokane Valley of Washing- 

 ton for the control of the fruit-tree leaf roller, and have been used 

 against this insect for 12 or 14 years in the Hood Kiver Valley of 

 Oregon. Although it is necessary to use the oil emulsion nearly twice 

 as strong for the leaf roller as for the scale, no injury has been evident 

 where the oil was properly applied. Very cold weather following the 

 application of oil sprays in the fall has resulted in injury, and occa- 

 sionally has killed the trees. Xo injury has occurred, however, from 

 cold weather following dormant spraying in the spring. The usual 

 frosty nights experienced in March and April have not resulted in 

 injury to oil-sprayed trees. Even temperatures below zero, follow- 

 ing an early February application of oil, have not affected the trees. 



A large amount of injury has resulted from the application of 

 lubricating-oil sprays to dormant trees after the buds have started 

 to open. This was especially true in 1925 when, on account of a 

 very early spring, a great deal of spraying was done after the buds 

 had separated, and even after some of the blossoms had opened. Used 

 at this time, oil sprays will cause more damage than lime sulphur, 

 although the latter will also result in much injury. Oil sprays, when 

 used at strengths suitable for dormant trees, should be used only 

 when the trees are practically dormant : that is, before the bud scales 

 have separated. 



This circular covers work done at Yakima. "Wash., during the sea- 

 sons of 1923. 1924, 1925, and 1927. Experiments were carried out 

 both in the laboratory and in orchards. 



