TREE HOPPERS AND THEIR CONTROL 13 



Sweetclover (Melilotus sp.), which is sometimes used in place of 

 alfalfa (Medicago sp.) as an orchard cover crop, would doubtless 

 prove preferable to alfalfa from the standpoint of tree-hopper con- 

 trol, as it lasts only two seasons, is less suitable than alfalfa for 

 tree-hopper food and protection, and perfectly clean cultivation is 

 entirely practicable following it. 



PRUNING AND COLLECTING 



Another control method which has been advised is to prune out 

 and destroy infested twigs. This is practicable to a limited extent 

 where only occasional twigs are infested, but to cut off all infested 

 twigs containing eggs would mean in many cases a very severe 

 cutting back of nearly all lower twig terminals, or, in case of 

 1-year-old or 2-year-old trees, their complete destruction. 



The use of hopper dozers to collect the insects has been suggested, 

 but this has been found impractical in the cover-cropped orchards. 



DORMANT SPRAYING AGAINST THE EGGS 



For controlling tree hoppers once they have become established 

 in an orchard, spraying the trees with a dormant oil spray, when 

 pruning or clean cultivation is impracticable, has been found effective 

 in killing most of the eggs. 15 Though 100 per cent of the eggs are 

 rarely destroyed with any spray treatment, enough of them are killed 

 to reduce the infestation considerably. Dormant sprays containing 

 4 per cent or more of oil, as used for the San Jose scale 10 or the 

 fruit-tree leaf roller, 17 have been found to kill from TO to 100 per 

 cent of the eggs when properly applied. Since lime-sulphur has been 

 found of little value in destroying tree-hopper eggs, it will be neces- 

 sary to make a special application of an oil spray to control these 

 insects in lime-sulphur-sprayed orchards or in orchards which would 

 otherwise be unsprayed. Extra applications of dormant oil sprays 

 for tree-hopper control are not necessary, however, since the regular 

 applications of these sprays will suffice if special care is taken to wet 

 thoroughly the infested twigs, most of which hang low in the case 

 of bearing trees and are often missed in spraying for the leaf roller 

 and the San Jose scale. 



SUMMER SPRAYS AGAINST THE NYMPHS 



The use of oil or nicotine, or the combination of both, against the 

 nymphs while they are feeding on the cover crop has been recom- 

 mended. Tests of these materials have given little if any control, 

 since the nymphs are entirely at the extreme base of the alfalfa 

 stems where these leave the soil, and _#re, therefore, not readily 

 reached with any spray. Inasmuch as most of the nymphs, upon 

 hatching, fall into the alfalfa underneath the tree, the value of 

 sprays directed against them would be increased by exposing them 

 by mowing the cover crop under the trees just before applying the 



13 YOTHERS, M. A. " TREEIIOPPERS," NEW ORCHARD PESTS IN THE PACIFIC NORTHWEST. 



Wash. State Hort. Assoc. Proc. 20 : 97-102. 1924. 



16 Aspidiotus pemiciosus Comst. 



17 Aichips argyrospila Walk. 



