ST. JOSEPH, La. – With more rain falling across the Mid-South in recent days, cotton producers are being advised to use caution in applying mepiquat chloride, especially on the taller, full-season varieties many are growing.

Speaking at the Northeast Research Station Field Day, Extension cotton specialist Sandy Stewart said much of Louisiana’s cotton is in the eight- to-11-node stage with some plants having 12 to 13 nodes. “But we also have cotton as small as this,” he said, pointing to a nearby test plot of just-emerged cotton in a planting-date study.

Like those in other states, Louisiana growers have begun to plant taller, full season varieties such as Deltapine 555 BG/RR and Stoneville 5599BR, said Stewart. “These varieties are different than what we had four or five years ago. They’re tall, true, full-season varieties and managing your Pix applications on them is a challenge,” he said.

As the state’s cotton is approaching the 12 to 15-node stage when Pix applications are normally made, said Stewart, an agronomist based at the LSU AgCenter’s Dean Lee Research Station near Alexandria. Stewart said he was using the generic term Pix to apply to applications of mepiquat chloride, Pix, Mepex, Pentia and other formulations.

Conventional wisdom says growers can apply mepiquat chloride at pinhead or matchhead square on the taller, full-season varieties without incurring as much risk of premature cutout as with older varieties.

“They’re more vigorous, and they don’t seem to have the risk associated with those early pre-bloom applications of Pix that some of the earlier, shorter-season varieties did – that you might induce early cutout if you ran into dry or real wet conditions following the first application.”

Even with the newer varieties, growers should exercise caution in making those applications, Stewart says.

“The saturated conditions and mild temperatures we’ve been under certainly have stunted and slowed cotton growth and development, but we don’t know how much damage might have been done to the root system,” he said.

“Cotton root activity is usually increasing at this time, but roots, especially the small, fibrous roots, may have declined under these saturated, anaerobic conditions. If we got another week or two of rainfall in here I think we would see a good bit of damage.”

The biggest impact of extensive root damage at this stage is usually the loss of drought and stress tolerance, Stewart notes. Plants aren’t able to reach deeper into the soil profile for moisture and begin to shed fruit to protect themselves.

“Right now I don’t know how much drought tolerance we have in this crop,” he said. “It’s probably OK, but there may be little drought tolerance due to the damage to the root system in some areas.”

LSU research on Deltapine 555 indicates growers have a window between 12 and 15 nodes (or roughly one to two weeks before bloom) when they should make their first mepiquat chloride application.

“Controlling plant height has not been that difficult in my experience when you make your first application at 12 to 15 nodes, taking into account the soil conditions and growing conditions that are occurring at that time,” he said.

“We’re on the front edge of that now,” he noted. “And given the saturated conditions, I think it’s best to wait a week or 10 days and evaluate what’s going to happen to this crop. If we dry out, and the crop begins to grow quickly, we can be as aggressive as we normally have been with these varieties.”

If it remains wet and the crop does not resume growing, he said, “We want to be more cautious with our Pix applications. We still have time because we’re just ahead of that 12- to15-node window that I believe is optimum for Pix applications.”

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