Heat Stress (HS) results when high temperatures combine with elevated humidity to increase crop temperatures.
Long term research by UA scientist established The Arizona Heat Stress Model. According to this model there are three potential stress conditions based on mean daily canopy temperature: 1) a no-stress condition when canopy temperatures average less than 82.4°F; 2) a Level 1 (L1) heat stress condition when mean canopy temperature falls between 82.4°F and 86°F; and 3) a Level 2 (L2) heat stress condition when canopy temperatures exceed 86°F.
Upland cotton is vulnerable to heat stress during the summer monsoon season in the low desert production areas (<2,500’ elevation) of Arizona. The primary impact of heat stress is a reduction in fruit retention which can: 1) reduce overall lint yields, 2) delay crop maturity, and 3) reduce lint quality.
Some L1 & L2 (HS) were reported during the last few weeks in different cotton production areas in the state. The 2013 Heat Stress updates are available at the following link:
http://ag.arizona.edu/AZMET/cotton.htm#HEATSTRESS
Here is a link to University of Arizona Cooperative Extension publication on Cotton Heat Stress: http://ag.arizona.edu/AZMET/az1448.pdf . This article is dealing with summary of relevant research on cotton heat stress, meteorological factors that contribute to heat stress, typical plant responses to heat stress, the Arizona model used to predict heat stress, possible management options for minimizing the impact of heat stress, and how to access online information on heat stress conditions.