Project Summaries

BOLL ROT OF COTTON

Kathy S. Lawrence, C. Dale Monks, Dennis Delaney, Katherine Glass, and Malcomb D. Pegues, Auburn University

Humidity within the cotton canopy during the period of flowering, boll development, and boll opening has a substantial influence on the incidence of boll rot. While the environment during the mid- to later part of the growing season cannot be controlled nor precisely predicted, cultivars may differ in their susceptibility to boll rot, and planting dates in combination with cultivar selection may be used to shift the principal period of flowering and boll development. Determining the relative susceptibility of cultivars to boll rot would provide growers with additional guidance concerning cultivar selection. Information concerning the epidemiology of boll rot could help growers select a combination of planting dates and cultivars to avoid possible periods of high infection. Moreover, recent research has suggested that certain fungicides applied during the flowering period have protected cotton bolls from floral infection and hard lock, a form of boll damage wherein the lint matures, but remains bound in the locules, and cannot be harvested efficiently with spindle pickers.  

The objectives were: 1) determine the environmental factors that induce boll rot on early and full season cotton cultivars; 2) determine cotton cultivar response and potential yield losses due to boll rot; and 3) conduct efficacy trials with fungicides to determine boll rot incidence and yield effects.

In 2005, early planting increased the cotton boll rot disease index for both early and full season cultivars. Hard lock incidence was also higher for the earlier planting dates than the later planting dates. However, seed cotton yields for both maturity classes of cultivars were higher when planting was done earlier than the last planting date of 3 June. Overall, boll rot and hard lock were more severe in the early season cotton cultivars compared to the full season cultivars. Tests with candidate fungicides applied during flowering showed that foliar sprays of Quadris 2.08SC^® or Topsin M^® reduced hard lock compared to that found in non-treated cotton. Treatments of either fungicide applied 2-4 times biweekly increased seed cotton yields compared to the non-treated cotton. An exemption from registration (section 18) to use these fungicides for management of hard lock will be prepared for submission in 2006.