Monday, September 14, 2015

Moving Toward the Final Stage Before Cotton Picking Time

If you look skyward around the Valley these days, you might see a few signs the cotton harvest is just around the corner. 

The sight is a crop duster buzzing the lush, green cotton fields, applying defoliants to the crop. That means we’re heading down the back stretch toward the day growers start picking the cotton lint.
A crop duster applies defoliant to a cotton field.
“It’s happening now,” field scout Carlos Silva says about the start of defoliation. “I’m seeing warning signs (to stay out of the treated fields.)”

It won’t be long before we’ll see harvesters in the fields. Usually, the cotton is ready to harvest about two to three weeks after defoliation.

Why do growers defoliate their cotton fields?

Well, defoliation helps the mature bolls open fully and ensures that lint is free from leaves and other trash. In the meantime, immature bolls will stay immature. The treatment 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 – or trash in industry parlance – collected during the harvest.

There’s a certain art and science to defoliation. 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. 

There's an art and science to defoliation timing.
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 is the last operation where management decisions can have a large impact on profit, a lot of dollars are hinging on making the right decision,” UC Integrated Pest Management says. Go to UC IPM online to learn about scheduling defoliation in cotton.
Sticky cotton remains a concern for growers.
 Meanwhile, Carlos says he is seeing a rise in aphids and whitefly in fields that haven’t been defoliated yet. He warns growers to keep on top of them to avoid honeydew build up and sticky cotton.

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