July 4, 2021 Cotton Advisories
The high pressure system driving the monsoon flow will shift northward into a less favorable position in the Great Basin this week. Expect warmer temperatures, lower humidity and reduced chances for precipitation this week. Precipitation will generally be confined to high elevation areas and temperatures will run 2-4 degrees above normal. The reduction in humidity and associated cloudiness should allow for slightly cooler night temperatures. That said, the combination of above normal temperatures and elevated humidity will produce some heat stress in low elevation production areas. 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 Cotton Heat Stress Update Report are available at the following link: https://cals.arizona.edu/AZMET/cot-HSrpt.htm. 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.
One change was implemented in this week’s advisories: the difference in heat unit accumulation relative to normal has been converted to days and is provided in the row beginning with the label: +/- Norm. None of the locations are running below normal at present. Many of the cotton fields are in the early bloom stage of growth, between ~ 1200 and 2000 HUAP. Thus far, early fruiting patterns have generally been good in most areas. The optimum N fertilization window is from ~ 700-2000 HUAP due to the most rapid period of crop N demand and uptake by the plant. Therefore, it is important to make an assessment in the field regarding stage of growth, fruiting patterns, and crop vigor. Fruit retention (FR) and height:node ratio (HNR) indices can be useful tools for monitoring the vegetative and reproductive balance in a cotton field. UA Extension guidelines are available for reference to FR & HNR levels in relation to stage of growth and HUAP. Petiole NO3-N indices are also available and important to use for crop N management. With the increasing humidity and higher night temperatures that have been experienced in the past week, it is important to watch for any loss in FR and/or an abnormal increase in vegetative growth. Water stress should be avoided and N fertilizer applications provided to support the developing fruit load in balance with vegetative growth. Consult UA CE publication for N management for cotton https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1200-2015_0.pdf, and reference to FR & HNR levels in relation to stage of growth and heat units accumulated after planting (HUAP) https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1207-2015.pdf and https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1218-2015.pdf.
Precipitation was more widespread across the Lower Colorado and Rio Grande Basins last week. Only light precipitation fell across much of the Upper Colorado Basin with the exception being the Upper San Juan Basin of Southwest Colorado.
The links below are for Cotton Advisories as of July 4, 2021 for different production regions in Arizona: