6 CIRCULAR 926, U. S. DEPARTMENT OF AGRICULTURE 



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Figure 4. — Irrigating vegetable plantings in a plot. 



danger of soil contamination, minimum quantities of insecti- 

 cides were used, and applications were made following cultural 

 operations. 



Tomatoes were treated from four to six times with a dust con- 

 taining 5 percent of DDT and 50 percent of sulfur to control the 

 tomato fruitworm (Heliothis armigera (Hbn.)) and the tomato 

 russet mite (Vasates destructor (Keif.) ) The same dust was used 

 on lima beans and onions for the control of general plant feeders 

 such as lygus bugs, the two-spotted spider mite (Tetranychus 

 bimaculatus Harvey), cucumber beetles, and thrips. To control 

 aphids and the iris whitefly on lettuce, peppers, and other crops 

 as well as diseases on potatoes, the plants were dusted periodically 

 with a mixture containing 1 percent of parathion, 5 percent of 

 zineb, 5 percent of DDT, and 15 percent of sulfur. Aphids on cole 

 crops were checked with a 10-percent nicotine dust and caterpillars 

 with a 5-percent DDT dust. 



TESTS ON DIFFERENT CROPS 



The specific treatments of the different crops and their tolerance 

 to insecticides applied to the soil in which they were grown are 

 discussed in subsequent sections. The numbers of plants and yields 

 in the treated plots each year are presented in tables 2-5. 



Lima Beans 



Lima beans — varieties Ventura and Fordhook 242 — were 

 planted on April 25, 1949, April 18, 1950, and May 8, 1951. The 



