Rates of Seed Treatment Insecticides and Control of Stewart's Wilt in Sweet Corn

Area of Science:

• Agricultural Entomology
• Plant Pathology
• Pest Management

Background:

• Stewart's wilt, a significant disease in sweet corn, can be managed using neonicotinoid insecticides.
• Seed treatments offer a targeted application method for insecticides, potentially reducing environmental impact and improving efficacy.

Purpose of the Study:

• To evaluate the effectiveness of various rates of neonicotinoid seed treatments in controlling Stewart's wilt in susceptible sweet corn hybrids.
• To compare the economic viability of Stewart's wilt control for sweet corn destined for processing versus fresh market consumption.

Main Methods:

• Conducted 11 field trials across Illinois and Delaware from 2000-2003, evaluating clothianidin, imidacloprid, and thiamethoxam at rates from 0.125 to 1.25 mg a.i./kernel.
• Assessed Stewart's wilt incidence in treated versus untreated sweet corn seeds.
• Performed regression analysis to determine dose-response relationships and economic break-even points for different crop values.

Main Results:

• Insecticide seed treatments significantly reduced Stewart's wilt incidence (50-90% control) compared to untreated seeds in most trials.
• Higher insecticide rates yielded only marginal improvements in control over lower rates, with clothianidin showing slightly superior efficacy.
• Economic analysis indicated that the value of control varied significantly between processing and fresh market sweet corn, with lower incidence thresholds for fresh market.

Conclusions:

• Neonicotinoid seed treatments are effective for managing Stewart's wilt in sweet corn.
• Optimal rates for processing sweet corn may be lower than for fresh market due to differing crop values and economic break-even points.
• Clothianidin demonstrated slightly higher efficacy than imidacloprid and thiamethoxam at equivalent application rates.