Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/6/2006
Publication Date: 6/9/2006
Citation: Bundy, C.S., Funk, P.A., Steiner, R.L. 2006. Impact of thermal cotton defoliation on late-season insect populations. In: Proceedings of the Beltwide Cotton Conferences, January 3-6, 2006, San Antonio, Texas. 2006 CDROM. p. 1344-1351. Interpretive Summary: Stickiness caused by excreta of silverleaf whitefly, Bemisia argentifolii (Bellows and Perring), and cotton aphid, Aphis gossypii (Glover), can make cotton difficult to spin and can lower regional market value for many years. This study was conducted to determine whether thermal defoliation could be used to control late season insect pests in cotton. Field populations were counted daily for two weeks on thermally defoliated, chemically defoliated and untreated plots of Widestrike cotton (PhytoGen 1517-99W). Lab counts of emerged pupae and adults were recorded from leaves that had been picked after each treatment and incubated in covered Petri dishes for one week. Adult emergence on incubated leaves was least for the thermal treatment and greatest for the chemical treatment. Field populations in conventional chemically-defoliated plots closely resembled those of the untreated checks, increasing somewhat for the first few days after defoliation before gradually declining. Chemical and untreated plot whitefly populations were well above economic threshold levels. Field populations dropped immediately in thermal defoliation plots and remained at or near zero throughout the study. Leaves of thermally defoliated plants were noticeably desiccated within 24 hrs, preventing whitefly migration from the surrounding area. Thermal defoliation killed adult and immature insects and their habitat, thus stopping insect activity that would lead to more stickiness.
Technical Abstract: The potential impact of heat mortality as part of thermal cotton defoliation was evaluated in comparison to chemical defoliation and an untreated check for silverleaf whitefly immatures and adults at two sites in New Mexico. Adult whitefly emergence was significantly less for leaves exposed to a thermal treatment than the chemical or untreated checks. In the field, whitefly populations in the thermal plots were reduced to near zero immediately after defoliation where they remained throughout the study. Whitefly populations in chemically-defoliated plots closely resembled that of the untreated checks, likely due to the late-season conditions of the plants and not an impact of defoliation. The relative maximum temperatures attained and heat units accumulated by thermal defoliation were compared at various locations within the canopy.