Effect of Insecticide Termination at 250, 350, and 450 Heat Units on Carbon Partitioning from Upper-canopy Leaves to the Developing Boll Load

COTMAN, a crop monitoring program for cotton, uses the concept of 350 heat units after anthesis of the last effective flower population at NAWF=5 for termination of insecticide applications. Research and field observations have indicated that terminating insecticides at 350 heat units after physiological cutout (NAWF=5) results in a higher yield than when terminating earlier or later, although evidence is lacking. Furthermore, it is hypothesized that insect damage to upper-canopy (above NAWF=5) squares results in improved partitioning of carbon to lower developing bolls (Kim and Oosterhuis, 1998). The objective of this 3-year study was to investigate the effect of different times of upper-canopy square removal after NAWF=5 on subsequent firstposition boll weights at the NAWF=5 main-stem node and seedcotton yields. The movement of carbohydrates from upper-canopy leaves with squares removed to developing bolls lower in the plant was followed using a 14C labeling technique.