Treatment interactions affecting endemic populations of annual grass and broadleaf weeds, corn rootworm larvae (CRW), corn earworm (CEW), European corn borer (ECB), and common rust in sweet corn were investigated in three field studies near Arlington, WI, in 1996 and 1997. In all environments, weed biomass was affected only by the weed control treatments with cultivation resulting in the highest weed biomass. Corn root damage was affected only by the CRW insecticide treatments in the early- and late-planted environments in 1997 (E97 and L97). Both weed control and ear insect (CEW and ECB) control treatments affected corn ear damage by CEW and ECB. In E97 and L97, more insect ear damage occurred in plots with 1× herbicide treatments than in cultivation treatments. In L97, the ear insect treatment decreased ear damage 55% compared to untreated plots. The interaction between ear insect and weed control treatments affected the number of CEW found per 10 ears in L97. The interaction between hybrid rust and weed control treatments influenced common rust severity in all environments. A hybrid rust by CRW by ear insect treatment interaction also affected common rust severity in E97 and L97. ‘Jubilee’ hybrid (rust-susceptible) corn treated with both insecticides had greater common rust severity than nontreated Jubilee corn. Sweet corn yield was affected most by weed control in all environments, with the lowest yields occurring in cultivated plots. Sweet corn yield did not differ between the 1× and ⅓× herbicide treatments in all environments. The interaction among hybrid rust by CRW by ear insect treatments also affected yield in E97 and L97. An important component of this interaction was the CRW treatment, as sweet corn yield was higher in treated than nontreated plots. The interactions in this study indicate that the best chances for developing comprehensive thresholds for sweet corn pests in the Midwest are for CEW, ECB, and common rust.
Nomenclature: Cyanazine; metolachlor; permethrin, (3-phenoxyphenyl) methyl ( ± ) - cis, trans -3- ( 2, 2-dichloroethenyl ) -2, 2-dimethylcyclopropane-carboxylate; tefluthrin, (2,3,5,6-tetrafluoro-4-methylphenyl)methyl-(1α,3α)-(Z-(±)-3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxylate; common rust, Puccinia sorghi Schw.; corn earworm, Helicoverpa zea Boddie; corn rootworm, Diabrotica spp.; European corn borer, Ostrinia nubilalis Hubner; sweet corn, Zea mays L. ‘Heritage’, ‘Jubilee’.