-2- 



have been completed by this week in this area. Many fields were observed with 

 from 20 to 50 percent of the plants infested, but a 75-percent infestation of 

 plants is the threshold for treatment. A large seed crop of first-generation 

 borers exists so that second-generation populations could be high in August. 

 The second-generation moths will concentrate their egg laying in the late-maturing 

 cornfields. The area most likely to experience second-generation corn borer dam- 

 age lies west of Highway 51 and north of Highway 460. 



Corn rootworm larvae continue to feed on corn roots. Damage has been reported in 

 a few fields of continuous corn where aldrin or heptachlor have been used for sev- 

 eral years. This indicates a continued buildup and spread of the resistance prob- 

 lem reported in past years. Two reports of rootworms killing small, newly emerg- 

 ing corn have been received. The worms were feeding on the underground portion 

 of the stalk, much like a wireworm, eating the heart and killing the plant. A 

 basal treatment with a phosphate insecticide cultivated- in may be helpful if dam- 

 age persists. 



In general, the worms are maturing rapidly and there will be little to gain from 

 applying a granular phosphate or carbamate insecticide (diazinon, phorate, para- 

 thion, disulfoton, Buxten) at the base of the plant as a lay-by treatment. The 

 exception to the rule is if the majority of the worms are still small. A mature 

 rootworm larva is about 1/2-inch long. 



Soybean Insects 



Leafhoppers are damaging both soybeans and small corn, particularly in western 

 sections. These small, green, "gnat-like" insects are the same leafhopper that 

 attacks alfalfa. They cause leaves to yellow and brown (die back from tip) when 

 severe. The term "hopper burn" is used to describe their injury on potatoes. If 

 needed, a spray containing 1 pound of malathion per acre for soybeans or 1 pound 

 of carbaryl (Sevin) per acre for corn will control this insect . 



Yellow and black grass thrips are still present on soybeans and in the whorl 

 leaves of corn. Their feeding appears as tiny, white streaks on the leaves. 

 They also can be found feeding in the flowers , and there is some evidence that 

 they may cause a distorted pod formation. Some soybean fields in southern sec- 

 tions have high populations (20 per leaf) and damage is evident. If plants be- 

 come seriously affected, use a spray of malathion at 1 pound per acre in soy- 

 beans or carbaryl (Sevin) at 1 pound per acre in corn. 



Two-spotted spider mites have been reported damaging soybeans in the west- 

 southwest section. Mites are more likely to become numerous when the weather 

 turns hot and dry. These mites appear as small black spots on the undersides of 

 leaves. Usually, a fine web is also apparent. Affected soybeans show stunting, 

 yellowing, and browning of leaves, but the infestation is usually spotty within a 

 field. Severely affected fields should be sprayed with 1/2-pound of azinphosmethyl 

 (Guthion) or 3/4-pound of carbophenothion (Trithion) per acre to control the mites. 

 These insecticides should be applied only by experienced operators, as they are 

 highly toxic. Azinphosmethyl has a 21-day waiting period between treatment and 

 harvest, carbophenothion a 7 -day waiting period. Do not feed soybeans sprayed 

 with either of these insecticides as forage to dairy animals or livestock fatten- 

 ing for slaughter. 



