Field Evaluation of Insecticides for Control of Larvae of Corn Rootworms

Larval Susceptibility of an Insecticide-Resistant Western Corn Rootworm (Coleoptera: Chrysomelidae) Population to Soil Insecticides: Laboratory Bioassays, Assays of Detoxification Enzymes, and Field Performance

“…In 1997, there was relatively high rootworm pressure at the Holdrege site; the untreated plots averaged 4.55 on the 1Ð 6 scale (Table 3). Although the relationship between root injury ratings and yield is quite variable, ratings of Ͼ3 suggest the potential for economic loss (Mayo 1986; see also Gray and Steffey 1998). Based on root injury ratings, all insecticides signiÞcantly reduced root injury compared with the untreated control.…”

Corn rootworms (Coleoptera: Chrysomelidae) in space and time

“…The minimum distance is dependent upon the scale of the study, but generally root damage by corn rootworm larvae can be similar within 4 m according to the semivariograms in small-and microscale studies. To evaluate postplanting insecticide treatments the most commonly used experimental design is a randomized complete block, replicated three to six times, with single-row treatments at several locations (Mayo 1986). This type of experimental design reduces possible trends in soil properties within the fields.…”

“…To quantify root injury by corn rootworm larvae, root-damage rating, root-pull resistance, larval counts, and percent lodged plants (Mayo 1986) have been used. The most widely accepted method has been root-damage ratings such as the Iowa root-damage rating (Hills and Peter 1971) and the 1-9 scale (Musick and Suttle 1972).…”

Effects of Row Spacing and Plant Density on Corn Rootworm (Coleoptera: Chrysomelidae) Emergence and Damage Potential to Corn

“…A root rating of 0.50 on the Iowa State University node-injury scale is equivalent to a root rating of 3.0 on the scale developed by Hills and Peters (1971) (Oleson and J.J.T., unpublished data). Root ratings Ͼ3.0 on the scale developed by Hills and Peters (1971) can result in an economic reduction in grain yield (Mayo 1986). Although adult emergence was signiÞcantly greater in the 38-cm rows, it did not translate into greater root injury (Table 4).…”