Submitted to: Environmental Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/27/2006
Publication Date: 6/1/2005
Citation: Snodgrass, G.L., Scott, W.P., Abel, C.A., Robbins, J.T., Hardee, D.D. 2005. Effects of Early Season Herbicide Treatment of Marginal Areas Near Field in the Delta of Mississippi on Broadleaf Weeds and Tarnished Plant Bug (heteroptera: miridae) Popualtions on Them. Environmental Entomology. 34:705-711. Interpretive Summary: The tarnished plant bug is a serious pest of cotton grown in the mid-South. Plant bugs are controlled in cotton exclusively with insecticides, and have become increasingly more difficult to control because of varying levels of resistance to organophosphate, pyrethroid, and carbamate insecticides. Having to treat cotton with insecticides for plant bugs has reduced benefits that growers have received from boll weevil eradication and the use of transgenic cotton to control lepidopterous pests. Non-insecticidal control measures are needed for plant bugs in cotton. In the present study, we determined that single application of an herbicide that selectively killed broadleaf weeds (that serve as early season hosts for plant bugs) in margins of fields, ditches, and roads in nine-square-mile areas of the Mississippi River Delta caused a significant reduction in the number of weed hosts, and prevented plant bug population buildups on weeds in the treated areas. After treatment of an area, the main host plant left was Italian ryegrass. Treatment of the marginal areas in March prevented plant bugs from utilizing Italian ryegrass as a host, since it does not bloom until mid-April, and plant bugs can not survive on it unless it is blooming. This research established that March was the best time to treat the wild hosts and measured the effect of the treatment on the hosts and plant bug populations associated with them. It was found in an additional study that cotton grown in areas that were treated had significantly fewer plant bugs than cotton grown in untreated areas.
Technical Abstract: A single herbicide (Trimec® or Strike 3') application in early season (March or April) was made to marginal areas around fields, roads, and ditches in 23 km2 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, Lygus Lineolaris (Palisot de Beauvois). The herbicide treatment caused a significant reduction in wild host densities in the treated test sites in all three years. Tarnished plant bug populations in treated 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 plant but populations increased in treated marginal areas in this year. The increase was thought to be caused by plant bugs moving to Italian ryegrass, Lolium multiflorum Lamarck, a previously unreported plant bug host, which was not affected by the herbicide. Laboratory tests showed that plant bug nymphs developed into adults on floral spikelets of ryegrass, and confirmed that ryegrass was a host. The filed test results showed that the herbicide application caused significant reductions in numbers of broadleaf wild hosts and plant bugs that utilized them, when the application was made during the first two weeks of March.