CULTURAL CONTROL OF EARLY SEASON WILD HOSTS REDUCES NUMBER OF TPB IN COTTON
The tarnished plant bug is a native insect which is very well adapted for survival in a large number of habitats in North America. It is becoming a primary pest of cotton in the Mississippi River Delta of AR, LA, and MS because of the success of boll weevil eradication and the widespread use of Bt cotton to control lepidopterous pests. In the Delta, plant bugs reproduce on broadleaf wild hosts in late winter and spring prior to their movement into cotton. Most of these wild hosts are found in marginal areas near fields, ditches, and roads. Management of these marginal areas that eliminates the wild hosts could reduce numbers of plant bugs available to move into cotton. Once in cotton, tarnished plant bugs can only be controlled with insecticides to which they are becoming increasingly resistant. Non-insecticidal control measures are needed to help preserve the benefits being derived from boll weevil eradication and Bt cotton. At the Southern Insect Management Research Unit, Stoneville, MS, ARS scientists Gordon Snodgrass, William Scott (retired), and Dick Hardee (retired) have been working to develop a cultural control program for plant bugs which could be used as an areawide program.
The cultural program being developed has centered on the destruction of broadleaf hosts in marginal areas near fields, roads, and ditches in March and April with a herbicide to reduce subsequent numbers of plant bugs found in cotton grown in treated sites. A large experiment was conducted in 1999-2001 in which four experimental sites, each nine-square-miles (three miles by three miles), were established each year. In two of the experimental sites each year, all of the marginal areas with wild hosts were treated with a single herbicide application which killed only broadleaf weeds. The remaining two sites were check sites each year. Tarnished plant bug populations on wild hosts and wild host density were determined prior to and after the herbicide application. Cotton grown in the four experimental sites was sampled weekly from the first week in June through the first week in August to determine numbers of plant bugs present. Insecticide control costs for plant bugs was obtained from growers in the four areas for comparison.
Results from the experiment showed that the herbicide application was effective each year and caused significant reductions in the density of the broadleaf hosts. In all three years, the most abundant grass left in the treated margins was Italian ryegrass. The herbicide application was made in April 1999, and when the broadleaf hosts died, tarnished plant bugs utilized Italian ryegrass (which was in bloom) as a host. To avoid this problem, the herbicide application was made in March of 2000 and 2001, at this time Italian ryegrass was not in bloom, and did not serve as a host. Tarnished plant bugs had lower mean numbers per sample in cotton in the treated sites in all but two weeks in 1999 and 2000, and in all but one week in 2001. Over all three years adults, nymphs, and total plant bugs averaged 45.5, 47.0, and 46.1% lower per sample, respectively, in cotton grown in the treated sites. The lower number of plant bugs found in the treated sites was not caused by increased insecticide use in cotton for plant bug control in the treated sites. In 1999, 2000, and 2001, grower costs for plant bug control in cotton were $6.47, $6.56, and $3.44 lower per acre, respectively, in the treated sites as compared to cotton grown in the check sites.
Benefit to cost analyses were performed by Mr. Fred Cooke, Economist, Delta Research and Extension Center, Stoneville, MS on data from the experiment. For every dollar spent in treating the wild hosts in the two treated sites in 1999, a benefit of $8.51 was obtained due to reduced insecticide costs for plant bug control. The benefit was $10.28 in 2000. In 2001, no economic benefit was obtained. Costs for insecticide control were lower in the treated sites through June of 2001, however, large populations of plant bugs moved into cotton throughout the Delta in July, and all economic benefits from the treatment of the sites were lost. In the three years of the experiment over 21,000 acres of cotton were grown in the treated sites. A total of $17,650 was spent for labor, herbicides, and equipment use to treat the margins in the nine-square-mile sites. Over the three-year period, growers in the treated areas saved over $115,000 in reduced insecticide costs for plant bug control in cotton.
Control of early season broadleaf wild hosts in marginal areas did not eliminate the need for insecticide use to control plant bugs in cotton grown in treated sites, but it did reduce this need, and produced an economic return to growers in the treated sites. As other non-insecticidal control measures become available, they will be evaluated by ARS scientists, separately, and in combination with early season control of broadleaf hosts.
EXAMPLES OF WILD HOSTS
For more information contact:
PO Box 346
141 Experiment Station Rd
Stoneville, MS 38776
Snodgrass, G. L., W. S. Scott, J. T. Robbins, and D. D. Hardee. 2003. Early season herbicide treatment of wild host plants in marginal areas near fields, roads, and ditches and reulting numbers of tarnisded plant bugs in treated and untreated areas. In Proc. Beltwide Cotton Prod. Res. Conf. www.cotton.org/beltwide
Snodgrass, G. L., W. S. Scott, J. T. Robbins, and D. D. Hardee. 2003. Suppression of tarnished plant bugs in cotton by treatment of early season wild host plants with herbicides in nine-square-mile areas of the Mississippi Delta In Proc. Beltwide Cotton Prod. Res. Conf. www.cotton.org/beltwide