Aldicarb (TEMIK), 2-methyl-2(methylthio-propionaldihyde o-(methyl)oxime, is a systemic insecticide used extensively for early season pest control in cotton throughout the Cotton Belt. There are conflicting reports about the growth responses of aldicarb on various physiological processes in cotton. A two-year study was conducted to evaluate the effects of aidicarb on growth, development and photosynthesis of cotton under insect free conditions.

Cotton (Gossypium hirsutum L.) plants were grown from seed in sterilized Leeper clay loam soil, using sunlit temperature controlled growth chambers (SPAR) at the USDA-ARS Crop Simulation Research Unit, Mississippi state during the summer of 1988 and 1989. Aldicarb at rates equivalent to 0.84 kg/h at planting followed by 2.24 kg/h at initial squaring was incorporated in rows at 0.3 cm depth. The day/night temperature cycles in the growth chambers were maintained at 20/12, 25/17, 30/22, 35/37 and 40/32 C.

During the growing season, measurements of plant height, number of nodes on the main stem, biomass accumulation in different plant parts were recorded at frequent intervals. Flowers were tagged as they appeared during the course of the experiment. Root growth appearing on the glass face of the soil bins was measured. Carbon dioxide fluxes were measured on the canopies at 15-minute intervals every day to calculate gross photosynthesis (Pg) and respiration. At the end of the season, detailed analyses on boll and square numbers and biomass accumulation in various plant parts were recorded.

Aldicarb-treated plants were more vigorous, and accumulated higher biomass earlier in the vegetative period compared to untreated plants at all temperatures. Plants treated with aldicarb exhibited higher main stem growth rates at all temperatures. Aldicarb increased Pg at all temperatures, the effect was greater at 25/17, 30/22 and 35/27 C day/night temperatures.

The total root weight at the end of the season was 21, 75, 32, 13, and 29% higher in aldicarb treated plants compared to control plants grown at 20/12, 25/17, 30/22, 35/27, and 40/32 C temperatures, respectively. Aldicarb treated plants had higher root weights at deeper soil depths at all temperatures, and the effect was greater at 25/17, 30/22, and 40/32 C temperatures compared to control plants. The branching and length of roots were also greater in the aldicarb-treated plants than their respective controls at different soil depths at various temperatures. Aldicarb promoted earliness, increased the number and weight of bolls and squares at all temperatures.