High temperatures of 110 F on May 21 and 22, 2005, were recorded in the Blythe, CA, area. This was a very rapid heat increase from the high 80s-low 90s temperatures experienced in the days/weeks prior to these dates. Low temperatures also jumped from the mid to upper 50s to low night temperatures of 69 and 70 F on May 23 and 24 respectively. These high temperatures and related heat stress resulted in abnormal cotton flowers in mid-June, being especially characterized by elongated styles and stigmas therefore being beyond the anthers.

Two different cotton variety trials being conducted in the Palo Verde Valley allowed data to be collected semi-weekly beginning June 17-20, with 100+ flowers per plot examined in each plot (four replications) of each of the 14 cotton variety entries. Every cotton variety had an average of 90+% of flowers expressing heat stress abnormalities (elongated styles) at the beginning of data collection even though the trials varied by planting date and location. Abnormal flowers were noted for several weeks.

Stigma locations relative to anthers were also measured, with some as much as 21 mm beyond the anthers. Varieties differed in their responses to heat stress as measured by elongation later in the summer. Limited data were also collected for fruit retention and correlated with length of stigma extension beyond anthers. Retention percentages decreased as distance between anthers/stigmas increased. Retention losses of individually marked flowers bolls earlier in season increased as season progressed.

Various foliar fertilizers containing calcium were also evaluated for effect on stigma elongations of DPL 449BR cotton. Significant differences existed for stigma elongations, with 2.5 qts./acre of CalMax resulting in statistical reduction of elongation when compared with the untreated check at 3 weeks after application. Statistical differences did not exist at four weeks after application however for stigma elongations beyond anthers, although statistical differences did exist at this date for percentage of flowers so affected, with highest percentage (81.7%) noted in untreated cotton.