Cotton Likes It Hot – But Only Under Certain Conditions

Some like it hot. Others not.

“It’s brutal,” field scout Carlos Silva says about the scorching 100 degree-plus weather that enveloped the San Joaquin Valley much of last week.Like many others who work outdoors, Carlos isn’t looking forward to another scorcher this week.

On the flip side, some do like it hot. Take cotton plants.

Cotton can thrive in really hot weather.  You might say it’s in the genes – cotton originated in hot, tropical climates and can live in very high temperatures, especially irrigated cotton.

Here’s a little science: The optimum air temperature range for cotton photosynthesis is 77 to 113 degrees. Photosynthesis, in short, is the foundation of plant life in which the sun’s rays are captured by the plant to create sugar necessary for growth.

The impact of high air temperatures on cotton really depends on the plant tissue. Like humans, cotton plants let water evaporate from its tissue – we call it sweat in humans – to stay cool. Well-water cotton plants have been found to be 10 degrees cooler than the air temperature, according to scientists. One study measured plant canopy temperature at 88 degrees on a blistering 121-degree day in Arizona.

Interestingly, the evaporative cooling of cotton in July can provide the same cooling output as up to 100 average home air conditioners, according to a July 1990 article by Kater Hake and Jeff Silvertooth in a National Cotton Council publication, Physiology Today. (The title is “High Temperature Effects on Cotton.) The key, they note, is maintaining an ideal tissue temperature range of 74 to 90 degrees. Another important factor is providing adequate water for the plant to use to cool itself.

The authors point out that yield and quality are tied to temperatures. By understanding the effects of hot spells on cotton, growers can make the timely adjustments on the production practices to maintain yield and quality. Dry soil, high humidity, bright sunny days, plant diseases and high night temperatures can play a role in tissue temperatures.

Checking moisture content in cotton.

Without adequate moisture, the plant can’t stay cool enough and that will impact yield.  “Hot” cotton is not good.

Quality, though, is less susceptible to hot temperatures, which often cuts short the boll setting process. That means fewer, poor quality late-set bolls.

During high temperatures, growers should keep the moisture high and surface soil moist. Too much water, though, will create waterlog conditions and can cause cotton to wilt and die. Growers need to keep an eye on fruit retention during hot weather, which will spur growth.

The bottom line advice: use frequent light irrigations during hot, hot weather.

Meanwhile, in the fields and orchards, Carlos and almond field scout Jenna Mayfield report relatively low pest pressures. They had anticipated a surge because of the heat wave.

Jenna says many orchards are showing signs of hull split. Carlos says the hot weather has spurred cotton and alfalfa growth this past week. Look for growers to start cutting alfalfa within the week.

In cotton, fruit retention remains good. But lygus bugs are still showing up in some fields and fruit drop is evident there. Growers will have to decide whether to treat, Carlos points out.

The exciting news is cotton plants are at first bloom. Soon we’ll start seeing cotton fields come alive with colorful flowers.