Cotton Experts Weigh in on Early Fall Rain in the Valley

Because of the unseasonably cool weather and early fall rain swooping into the San Joaquin Valley this week, we are publishing a special post updating growers about the weather's impact on this year's cotton crop. We thank two leading California cotton experts for providing their perspectives and tips.

Dr. Pete Goodell, University of California Statewide Integrated Pest Management advisor, Kearney Ag Center: Westside Fresno and Merced counties received between 0.35 inches at the UC West Side Research and Extension Center in Five Points and 1.28 inches in Los Banos.

Dr. Pete Goodell

In general, a half inch is considered good for cleaning dust, dirt and honeydew off plants. However, if cotton is still green with defoliation weeks away, rainfall could wash more dirt and honeydew onto lint.

If defoliation has occurred, this will affect efficacy due to lower temperatures. It might also cause some re-greening as plants receive some limited moisture. If defoliation and harvest is still a ways off, it might have no effect.

The bottom line: It all depends on location, amount of rainfall and condition/maturity of crop.

Bob Hutmacher, UC statewide cotton specialist: Lower temperatures and the start of rain bring some challenges to getting this cotton crop harvested and out of the field.

Bob Hutmacher

Lower temperatures slow the rate of maturation of later developing bolls, making it harder to get them open and ready for harvest. The cooler weather also means that chemicals like Ginstar don’t work quite as well as harvest aids. As a result, you may need to consider higher application rates at lower temperatures (such as with Ginstar), or if temperatures drop well below 80 degrees, you may do better by changing to different harvest aids (defoliation/prep combination, for instance) that work better at lower temperatures.

Rain is always a threat as we prepare for harvest. In some cotton varieties, cotton is held relatively “loose” in the boll and the added weight of rain can cause the cotton to “string out” even more than would otherwise occur. This brings the real threat of cotton dropping to the ground instead of hanging on the plant waiting for the picker. Fields usually hold up pretty well through the first rain, but repeated rains can result in some significant losses, particularly those varieties with loosely held cotton and fully mature bolls (such as some of the Acalas). Try to stage harvests to get the worst-affected fields harvested first, before losses can become more severe.

Storm clouds hover over Firebaugh area Thursday morning.

To be harvestable, some of the really late-developing cotton bolls need some additional heat units to fully mature and be ready to open up as we apply harvest aids. If there are too few heat units for the really late bolls, such as some of the late bolls in the upper canopy on Pima plants this year, it is unlikely that those can be opened for harvest no matter what combination of harvest aid chemicals are used.

In many parts of the San Joaquin Valley this year, particularly in Pima fields, there may be more second-picking of cotton fields, as the growers get the first picks out of the way during better weather and then see if a second pick might be a possibility for later maturing bolls.