Monday, September 24, 2018

Harvest Moon Arrives as Growers Prepare to Defoliate Cotton Fields

 Gaze into the sky tonight and you’ll see a spectacular full moon ablaze.

With fall only a few days old, the harvest moon shining bright tonight and tomorrow is a sure sign for cotton growers that their crop soon will be ready for picking.

“Growers should start defoliating their fields this week,” says field scout Damien Jelen.  The sure sign for folks driving around the Valley are warning signs placed around the border of cotton fields warning workers and the public about upcoming chemical applications. Two to three weeks after defoliation, the crop will be ready for picking.

Why are defoliants used to help with the harvest?

The treatment is a traditional cotton management practice that causes the leaves to drop and plant to start drying. This helps the harvesting machines pick the cotton cleanly off the plants and lessen the amount of leaves and debris (we call it trash) collected during the harvest. The practice improves the quality of the fiber as it is processed at the cotton gin.

You might describe defoliation as both an art and a science. If growers defoliate too early, their yields can be affected because there are too many immature bolls left on the plants. If the field is defoliated too late, the field could wind up with pest damage. 

A common guide to determine when to defoliate is using a Nodes Above Cracked Boll (NACB) method. Find the highest first position boll that is cracked and showing lint and then count the number of harvestable bolls above it. It’s fairly safe to defoliate at three NACB for the Pima varieties and four for Acala.

Some growers, however, may opt to defoliate early. They may worry about aphid and whitefly populations threatening the crop and causing sticky cotton problems – figuring they can sacrifice a little yield in order to get a head start on harvesting.Of course, there are advantages for holding off with defoliation and allowing more fruit to mature. Either way, it’s a decision that’s not taken lightly by growers.

Defoliation of local cotton fields is ramping up.
“Defoliation is the last operation where management decisions can have a large impact on profits;a lot of dollars hinge on making the right decision,” UC Integrated Pest Management says.

Here’s what UC IPM considers the best conditions for defoliation:

  • Moderate to high air temperatures (daytime greater than or equal to 80 degrees, nighttime greater than 60 degrees)
  • Relatively low plant and soil nitrogen levels
  • Moderate soil water levels (plants not water stressed)
  • Relatively uniform crop development; plants at vegetative cutout with limited or no regrowth
  • Weeds, insects, and diseases under control
  • Ability to get good chemical coverage and penetration of the chemicals into the plant canopy

Pest control advisors and UC extension specialists can offer recommendations about defoliant products and application rates.

Growers monitor for sticky cotton.
Meanwhile, Damien says aphids and whitefly populations have been under control. That’s important in fields that haven’t been defoliated yet. “You need to keep monitoring for these pests to avoid honeydew build up and sticky cotton,” Damien says.

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