Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/1/2003
Publication Date: 7/1/2003
Citation: Snodgrass, G.L., Scott, W.P., Robbins, J.T., Hardee, D.D. 2003. Early season herbicide treatment of wild host plants in marginal areas near fields, roads, and ditches and resulting numbers of tarnished plant bugs in treated and untreated areas. National Cotton Council Beltwide Cotton Conference. Interpretive Summary: Tarnished plant bugs are major pests of cotton in the midsouth. They are controlled in cotton exclusively with insecticides, and are becoming increasingly more expensive and difficult to control because of resistance to many of the insecticides used in cotton. Control measures not based solely on insecticide use are badly needed. One possible control method is by the use of herbicides in marginal areas near fields, roads, and ditches to destroy broad leaf weeds on which plant bug populations buildup in the winter and spring prior to moving into cotton. The current study found that a single herbicide application was effective in significantly reducing densities of broadleaf weeds found in marginal areas in nine-square-mile areas of the Delta in 1999, 2000, and 2001. Tarnished plant bug populations were also reduced significantly in the treated marginal areas when the herbicide application was made in March 2000 and 2001. When the application was made in April 1999, plant bugs moved from broadleaf weeds as they died onto flowering Italian ryegrass. This grass was not affected by the herbicide application and is very abundant. It also served as a plant bug host in this year. The herbicide application and evaluation of its effect on weed hosts and tarnished plant bugs that utilize them, was part of a large experiment that determined that the reduction in early season numbers of plant bugs by the herbicide treatment also resulted in lower numbers of plant bugs in cotton grown in the treated area as compared to numbers found in cotton grown in untreated areas.
Technical Abstract: A single herbicide (Trimec® or Strike 3) application in early season was made to marginal areas around fields, roads, and ditches in 23 square kilometer (9 square miles) test sites of the Mississippi Delta in 1999, 2000, and 2001. The herbicide was used to kill broadleaf weeds in the marginal areas which served as food and reproductive hosts for tarnished plant bugs. The herbicide was effective and caused a significant reduction in wild host densities in the treated test sites in all three years. Tarnished plant bug populations in treated test sites did not increase significantly in the treated marginal areas during April and May following treatment of the margins in the first two weeks of March in 2000 and 2001. Significant increases in plant bug populations occurred on wild hosts in the marginal areas of the untreated test sites in both years. The herbicide application was made in the first two weeks of April 1999, and in this year plant bug populations increased in treated marginal areas. The increase was caused by plant bugs moving to Italian ryegrass which was not affected by the herbicide. Ryegrass is abundant in marginal areas in the Delta and blooms during April. These results showed that the herbicide application was effective in reducing numbers of broadleaf wild hosts and plant bug populations that utilized them. To be most effective, the application should be made in late-February through the first two weeks of March to avoid moving plant bugs onto Italian ryegrass when it is in bloom and can serve as a host.