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Late start may signal extra defoliation effort

When a cotton season starts late like this season, the finish line becomes much more important.

Fortunately, the San Joaquin Valley crop has just about caught up and is expected to finish about where growers expect a normal season to end up.

Stands are now vigorous and fairly uniform. A hot July helped the season catch up from the late start.

“We may be a week behind in some places, but overall, it’s about normal in terms of maturity, and cutout is generally right on schedule,” says Tulare County University of California Cooperative Extension Farm Advisor Steve Wright. “We’re still waiting to see the full impact of the extreme heat on fruit retention. I expect the string of triple-digit days we had in July will cause the plants to abort some squares and young bolls. When that happens, we expect to get a surge of secondary growth that could create problems with defoliation.”

Growers’ harvest aid strategies will depend on what transpires in the next few weeks. However, it’s doubtful that one application will get it done this year, according to Wright.

“I’ve seen some years where we’ve had a strong boll load and uniform cutout with very little secondary growth when just about anything worked with one application,” he says. “I don’t think we’ll see that this year because of the heat we had in July. If we end up losing the top quarter of the crop – which I think is likely – the top could take off again. If that happens, it will most likely take two applications to shut it down.”

In addition to the standard defoliation options, some pest control advisers have been trying a new approach developed by Bayer CropScience technical service representatives. The Ginstar “two-shot system” was designed to simplify harvest aid decisions, facilitate better leaf drop and prevent re-growth.

“The first shot is a combination of 10 ounces to 16 ounces of Finish 6 Pro and 3 to 6 ounces of Ginstar applied when you would normally start defoliation,” explains Manuel Jimenez, Bayer tech service representative. “Temperature is also important. For best results, the first shot should be applied when daytime highs are in the 80s and are forecasted to remain there for the next seven to 10 days. Then the second shot is applied seven to 10 days later with a full defoliation rate of Ginstar (6-12 ounces) and ethephon (Prep).”

Jimenez adds that within this recommendation the user must keep in mind that the maximum amount of Ginstar allowed per season is 16 ounces and the maximum amount of ethephon allowed per season is 2 pounds active ingredient.

The idea is to knock off the top leaves with the first application, which opens up the canopy for more thorough coverage on the second shot. It usually eliminates the need to come back with a third application of sodium chlorate or paraquat typically used as a final burndown in a sequential defoliation program.

“It’s an innovative approach,” Wright says. “Last season, this strategy did very well in our studies. We’ll look at it again this year in our defoliation trials in mid-September. There will be some fields that are not moving fast enough toward cutout where I expect they will need two to three applications, like was used last season. In this approach, we begin defoliation sooner than the optimum timing.”

“We started using this system on vigorous cotton fields because they are typically more difficult to defoliate,” Jimenez says. “It’s also a good system to use in warm temperatures. While higher rates and harsher materials may end up frying leaves under warm temperatures, the ‘two-shot system’ minimizes that problem and results in a better defoliation job.”

It is also well suited for Pima, which is more difficult to defoliate than Acala.

“The rates may be a little higher on Pima because it is typically defoliated later in the season when temperatures begin to drop,” Jimenez says. “There’s a lot more foliage on Pima, so it really lends itself to this approach of taking the top off in the first shot so you can come in and do a more thorough job with the second shot. It is also very good at minimizing re-growth, which can support late season insects resulting in sticky cotton.”

With the end of the season in sight, Wright and others from UC are reminding PCAs and growers to remain vigilant in scouting and treating whitefly and late season aphid populations.

“It’s been pretty clean so far, but warmer temperatures and re-growth are conducive to problems,” Wright says.

The educational efforts on the part of the University of California and industry organizations such as California Cotton Ginners and Growers Association (CCGGA) have been very effective at mitigating the sticky cotton problem in California.

“Whitefly and aphid populations are always a consideration as the California cotton crop nears the end of the season,” says Earl Williams, president and CEO of CCGGA. “Those pest concerns are particularly worthy of attention in a year such as this since we got off to a late start and the entire production spectrum has been pushed later into the season. However, we do not anticipate any problems with sticky cotton because our PCAs are so keenly aware of the potential for late season whiteflies and aphids, and they know how to take care of it.”

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