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Late-season decline causes numerous as its names

A malady that shows up in San Joaquin Valley cotton fields each year goes by several names, late-season decline, late-season collapse and foliar decline are the most common ones.

University of California Extension Cotton Specialist Bob Hutmacher said the only thing that is more numerous than its name is its causes.

Hutmacher told consultants and growers at the recent Bayer CropScience Cotton Technology seminar in Carmel, Calif., that the severity of the problem can range form mild symptoms to complete late season defoliation.

Initially, it was isolated primarily to Pima cotton. Now it has shown up in Acala fields.

"It is difficult to identify one cause. There seem to be many causes," said Hutmacher, but they can be lumped under heading — stress — whether it be from heat, water, nematodes, insects, or lack of nutrients.

Physiological factors can compound those stresses.

The primary one being high boll loads on relatively small plants.

Boll retention was extremely high last season and that put stress on the plant to maintain and mature those bolls.

Plant pressure

"More and more fields are producing three and a half- to four-bale crops. These high boll loads are putting more pressure on the plant," leading to possible late-season collapse, he said.

Hutmacher recommends several approaches to minimizing late-season decline.

One is evaluate field for soil potassium and another is to see if there are restricted root zones related to management practices and rectify those if those problems are identified.

He also recommends growers evaluate fields with a history of late-season decline for variety susceptibility, especially in high yielding situations.

Hutmacher said water run applications of nitrogen and foliar applications of potassium at bloom have shown to delay the onset of late-season decline in susceptible fields.

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