Control of European Corn Borer and Twospotted Spider Mite in West Central Nebraska, 1991

Various pesticides were applied to field corn in two fields in west central Nebraska. Pesticides were applied to field 1, near North Platte, to blister stage, (R6 stage) ‘Pioneer 3475’ hybrid field corn on 4 Aug. Treatments were applied with a CO2-charged backpack sprayer through 8001 flat fan nozzles at 206,786 Pa (30 PSI), in a total volume of 196,405 ml/ha (21 gal/acre). Each treatment was applied to 3 by 10 m plots, replicated 3 times in a randomized complete block design. A total of about 40 first instar European corn borer (ECB) larvae was applied to 4 randomly selected plants within each plot, in corn cob grit, to the collars of the ear leaf and the leaf below, 1 day prior to pesticide application. Twospotted spider mites (TSM) were applied 3 days prior to treatment by tying 2 mite infested leaves to each of 2 plants within each plot. Since mite infestations were made close to the time of application no pre-treatment counts were conducted. Size of mite colonies were rated on the underside of three leaves below the ear, the ear leaf and two leaves above the ear at 7 and 14 DAT. Ratings were made on a 0-6 scale where 0 = no mites, 1 = individual mites, 2 = small colonies, 3 = large, individual colonies, 4 = large connected colonies but not covering the underside of the leaf, 5 = colonies completely covering the underside of the leaf, 6 = leaf dead due to spider mite damage. In addition to the spider mite colonies, spider mite predators were also counted. To evaluate the effectiveness of treatments in control of ECB larvae 4 artificially ECB infested and four randomly selected corn plants were collected from each plot four weeks post application. Each stalk was then split from root to tassel and the number of ECB larval cavities were counted. In a second field, near Hershey, Nebraska, insecticides were applied by center pivot injection on 13 Aug to soft dough stage (R7 stage) ‘Jacques 7710’ and ‘Jacques 7770’ hybrid field corn. Treatments were applied with a Pulsa diaphragm injector pump in a total volume of 9,353 ml/ha (1 gal/acre). One treatment also required the addition of 2,338 ml/ha (1 qt/ha) Veg-oil emulsified crop oil. These mixtures were sequentially injected, at a rate of 520 ml/min (18 oz/min), into a Zimmatic irrigation system, equipped with Rainbird impact sprinklers, making a 0.64 cm (0.25 inch) water application. Two replications of each treatment were applied to 8 acre pie shaped plots arranged in a randomized complete block design. Negotiation with the cooperator necessitated 2 slightly smaller check plots. Within each plot 4 randomly selected plants were artificially infested with a total of ca 40 first instar ECB larvae. These larvae were applied in corn cob grit to the collars of the ear leaf and the leaf 1 below the ear 3 days prior to pesticide application. Four weeks post application 4 artificially ECB infested and 5 randomly selected plants were collected from each plot. Each stalk was then split from root to tassel and the number of ECB larval cavities were counted.