Submitted to: Subtropical Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/31/2003
Publication Date: 5/1/2004
Citation: Greenberg, S.M., Smart, J.R., Bradford, J.M., Sappington, T.W., Norman, J.W., Coleman, R.J. 2004. Effects of different tillage systems in dryland cotton on population dynamics of boll weevil (Coleoptera: Curculionidae). Subtropical Plant Science. 55:42-49. Interpretive Summary: Cotton production in the United States continues to be limited by boll weevil populations which were responsible for crop losses and pest management costs exceeding $388 million in 2000. The use of conventional insecticides is the predominant crop protection strategy against boll weevils, but novel tillage systems and other farm management practices are needed to further enhance pest management. However, little is known about the effects of tillage systems on boll weevil populations in dryland cotton. We found that cotton plants in a conventional tillage system allocated more resources into vegetative growth while a conservation tillage system promoted fruiting at a higher rate. Plants grown in a conventional tillage system significantly increased light interception and shading of the soil surface, and significantly decreased soil surface temperature between the rows than plants grown in a conservation tillage system. Conservation tillage cotton produced more bolls and lint, and had fewer boll weevils than conventional tillage cotton. Conservation tillage in dryland cotton agroecosystems contributes to lower boll weevil populations by adversely affecting the life cycle of the insect through habitat modification.
Technical Abstract: Studies were conducted to determine the effects of a conservation tillage system in dryland cotton on soil surface temperatures, soil moisture, plant canopy structure, light interception, timing of fruit set, and how these factors affect crop yield and boll weevil, Anthonomus grandis grandis Boheman, populations compared with a conventional moldboard tillage system. Soil moisture at the 10-40 cm depth was 1.6 -1.9-fold higher in the conservation tillage treatment than in the conventional tillage treatment throughout the first 90 days of crop growth due to the decreased water evaporation from crop residue mulch. The conventional tillage cotton treatment had a greater water stress causing plants to shed squares and bolls. Cotton plants in the conventional tillage treatment allocated more resources into vegetative growth while the conservation tillage cotton responded by fruiting at a higher rate.. At 110 days after planting the conservation tillage cotton had an average height of 42.4 cm per plant versus 63.0 cm in conventional tillage, and the number of leaves per plant was 32.4 versus 51.7, while fruit numbers were 13.0 versus 7.1, respectively. Increased plant height and number of leaves in the conventional tillage provided significantly more light interception and shading of the soil surface, in the conservation tillage cotton 60.2% of the incoming sunlight reached the soil surface while the conventional tillage had only 36.2%. Therefore, the average soil temperatures between the rows in conservation tillage cotton were 8-11ºC higher than in conventional tillage and significantly influenced boll weevil mortality in infested squares shed from plants. The number of boll weevils per plant was 2.3 to 3.4-fold higher in the conventional tillage compared with the conservation tillage. Trap counts of weevil populations followed a similar trend with 1.6 to 2.8-fold more weevils in the conventional tillage compared to conservation tillage. The mortality of boll weevils in fallen, naturally infested squares, and in cohorts of laboratory-infested squares collected from the middle of the rows was 1.5-1.8-fold higher in conservation tillage field than in conventional. Percent punctured squares by boll weevil during the growing season averaged 2.1-fold higher in conventional than in conservation tillage fields.