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.

The adoption of precision technologies that spatially register measurements using global positioning systems (GPS) greatly facilitates conducting large-scale on-farm research by farmers. On-farm experiments that utilize producer equipment include variations in agronomic practices that occur in situations where we want to predict the effect of inputs on yield. The domain of inference for such on-farm studies therefore more closely matches that desired by researchers. To investigate the feasibility of on-farm research using GPS, a study was conducted to evaluate the potential benefit of site-specific weed management. The study utilized producer-maintained field-scale equipment on four Montana farms in dryland spring wheat production. Paired site-specific and whole-field herbicide treatment areas were established in 0.9 to 1.9-ha blocks using consultant weed maps and a geographic information system (GIS). Yield was unaffected by herbicide treatment strategy (site-specific or broadcast). Minimal detectable yield differences were evaluated for the experimental design (0.2 T ha−1). Net returns increased when the percentage of field infested by wild oat decreased. Visual ratings of wild oat density taken at harvest indicated no difference in wild oat control between treatments in two of four site-years. This research suggests that producer-owned equipment can be used to compare treatments, but the accuracy and subsequent power of such comparisons are likely to be low.

Managing weed infestations in a spatially precise manner requires accurate and cost-effective weed identification techniques. The goal of our research was to quantify the accuracy of continuous weed presence–absence maps and assess how management based on those maps may affect producer net returns. Each continuous sampled map covered the entire field and contained vector polygons labeled as either wild oat presence or wild oat absence. The accuracy of the continuous wild oat maps at each sampling time was determined from georeferenced quadrats of wild oat densities. The accuracy of the continuous wild oat seedling maps ranged from 48.3 to 87.1% among the six site-years. The accuracy of the wild oat seedling maps improved by at least 8% when a 10-m buffer was included around areas mapped as wild oat presence. The accuracy of continuous wild oat panicle maps from the combine at harvest ranged from 65.8 to 90.9% among the six site-years. The variation in accuracy for the wild oat seedling maps among sites was greater than the accuracy of the panicle maps. Net returns ($ ha−1) for four site-years were calculated and compared for four possible weed management approaches on each field. A site-specific herbicide application to areas mapped as wild oat presence always generated higher net returns than a herbicide application over the entire field for four sites. A site-specific herbicide application to areas mapped as wild oat presence plus a surrounding 10-m buffer area only resulted in a higher net return in one of the 12 site-years compared with a site-specific herbicide application without the 10-m buffer. This site had the lowest (48.3%) wild oat seedling map accuracy, and uncontrolled wild oat had a high-yield effect. This research indicates that using a continuous weed sampling method based on presence or absence for site-specific herbicide application can be profitable over a herbicide application to the entire field, even with the associated technology cost and seedling map errors.

Field studies were conducted at Arlington, WI, in 1996 and 1997 and at Georgetown, DE, and LeSueur, MN, in 1997 to determine weed control efficacy, crop injury, and yield response of PAT-transformed sweet corn to glufosinate-based weed management. Sequential applications of glufosinate 10 to 18 d apart at 0.4 and 0.3 kg ai/ha controlled common lambsquarters, common ragweed, velvetleaf, wild-proso millet, and fall panicum 90% or better at all locations. Weed control varied little among 0.3, 0.4, or 0.3 and 0.3 (sequential) kg/ha glufosinate rates. Glufosinate applied alone, with, or following atrazine controlled velvetleaf 90% or greater but was less consistent on common ragweed and common lambsquarters (73 to 100%). Atrazine plus metolachlor applied preemergence (PRE) and glufosinate applied alone postemergence (POST) provided inconsistent wild-proso millet and fall panicum control (43 to 99%). Metolachlor followed by glufosinate improved consistency of grass control (> 76%). Glufosinate followed by cultivation provided 80% or greater control of velvetleaf and wild-proso millet. Glufosinate did not injure or delay maturity of PAT-transformed sweet corn. Sweet corn treated with glufosinate resulted in yields greater than or equal to the sweet corn that was hand-weeded or received a standard herbicide treatment.

Field studies at Arlington, WI, and LeSueur, MN, were conducted in 1996 and 1997 to evaluate tolerance of six sweet corn hybrids to RPA 201772 applied preemergence at 79 to 210 g/ha. Both years the most sensitive hybrid at the Wisconsin site was ‘Zenith,’ with yield reductions of 14 and 22% at 210 g/ha (twice the labeled rate). ‘Excellency,’ ‘Green Giant 43,’ and ‘Jubilee’ tolerated RPA 201772 at 158 g/ha or less. The least tolerant hybrids in Minnesota were ‘Green Giant 6′ and Jubilee, and the most tolerant hybrids were Green Giant 43 and ‘Rogers 9056.’ Injury from RPA 201772 increased as application dose increased. The greatest risk of injury from RPA 201772 appear to be with Green Giant 6, Zenith, and Jubilee, especially on coarser textured soils with low organic matter. Excellency, Green Giant 43, and Rogers 9056 appeared to be the most tolerant. Because of the differential hybrid response to RPA 201772 across sites and years, more hybrid response data needs to be generated before RPA 201772 is labeled in sweet corn.