INSECTS INJURIOUS TO POTATOES AND TOMATOES 289 



Control. From the life history and habits it is obvious that 

 clean farming is the only method of effectual control. The 

 destruction of weeds and fall plowing should prevent any general 

 injury. Usually the injury is but local, and fortunately the 

 caterpillars are attacked by numerous parasites which aid in 

 their control, sometimes to the extent of killing 70 per cent of 

 them. In small gardens the prompt destruction of infested 

 plants will prevent the caterpillars from migrating to others. 

 Where weeds are infested in or near a crop they should be destroyed 

 as soon as cut, for if left on the ground the larvae will promptly 

 migrate to the nearest plants. Where fields are kept clean of 

 weeds there will be little trouble.* 



The Potato Tuber-worm f 



The most serious pest of the potato in California is the Tuber- 

 worm, which in tobacco regions of the Southern States is known 

 as the "split worm " or leaf -miner (see page 237). Xot infre- 

 quently 25 per cent of the crop is lost in infested regions in 

 California, injury occurring both in the fields and to the tubers 

 in storage. As the pest is carried in the potatoes and breeds in 

 storage throughout the warm winters of California, and when 

 exported across the Pacific, it is necessary to closely inspect 

 potatoes from infested regions. Although no injury to potatoes 

 has occurred outside of California, and though the insect probably 

 could not exist in the North, it may well be guarded against in 

 the Southern States, where it is a common tobacco pest.J 



Moths which have developed from larvae working in stored 

 potatoes are on the wing when young potatoes are up, and lay 

 their eggs at the base of the leaves. The young larvse bore into 

 the stalks, often causing the plants to wilt and die. On older 



* See Forbes, 23d Report State Entomologist of Illinois, p. 44; Washburn, 

 12th Report State Entomologist of Minnesota, p. 151 ; Journal Economic 

 Entomology, III, p. 165; Smith, Report N. J. Agr. Exp. Sta. for 1905, pp. 

 584-587. 



f Phthorimea operculella Zell. See W. T. Clarke, Bulletin 135, California 

 Agr. Exp. Sta. 



^Recently serious injury by this insect has been reported to potatoes 

 near Hallettsville, Texas. 



