"Late-season decline," a mysterious stress condition emerging in scattered Pima cotton fields in the southern San Joaquin Valley in recent years, is something new for growers to keep an eye on.

Bob Hutmacher, University of California Extension cotton specialist, says he and others studying it don’t really know what it is or exactly what to call it.

The reason for the decline, which resembles plants nearly ready for defoliation, he said, may be any one or a combination of various problems, including nutrition, planting date, hot weather, cultivation, varietal susceptibility, or crop rotation.

"It amounts to a high demand for something that the plant has difficulty keeping up with. We’ve seen it on both large and small plants," he said, adding that it has appeared where shoot growth somehow outpaced root growth to support it.

Speaking at the recent Pima Production Summit, 2004 at Visalia, Hutmacher said one frequent trait of affected plants is evidence of low nitrogen, potassium, or phosphorous.

Typically, it shows up late enough to have little more than cosmetic effect on the crop, but Hutmacher added that if it occurs earlier it can have impact on yield, as seen in some fields in Kern and Tulare counties. It has also occurred in Acala varieties.

Mid-bloom nitrogen

"A number of growers have had success in delaying the problem, if not eliminating it, with mid-bloom applications of water-run or foliar nitrogen," he said. These split applications were of 30 to 40 pounds of N.

For other strategies to head-off the condition, he suggested reducing practices that restrict root zones or prune roots and evaluating potential causes due to crop history, disease, and nematodes.

Whatever is done should relate to yield performance and not just symptoms, he said, noting that the varieties used in the SJV include a large range of growth types and growers manage them differently.

"Green plants with little boll load out there may grow through this just fine, but on some varieties with a heavy boll load you can watch the problem evolve."

Hutmacher also said a new strain of Fusarium wilt, Race 4, has been identified in California. "It strikes younger seedlings and can cause significant damage without being associated with nematode problems."

In some fields where the new wilt -- which pathologists say is not a variation of the Australian strain -- occurred, rootknot nematode populations were quite low.

USDA and commercial seed company plant breeders are at work screening varieties for the new pathogen, and greenhouse evaluations will be done when field sites are not available.

Water potential

Turning to irrigation to manage growth in Pima, Hutmacher cited historical data showing the limit for leaf water potential to be in the 23-24 bar range. "Better yields have occurred with water potential around 20 or 21 bars during late square through late bloom."

Deficits, however, are most severe during boll filling, when some of the worst vegetative growth problems occur in Pima.

He said managing plant water stress may be too extreme in the case of Pima where second, third, and fourth position fruit is critical for yield.

Growers may want to consider using a combination of water stress and Pix, but they should remember that too much of either, particularly in a high yield potential situation, reduces fruiting sites and, to some extent, yield.

Brian Marsh, Kern County farm advisor, told summit participants of his "work in progress" on adapting collection of plant mapping data to computers.

Portions, but not all, of the existing programs for Acala can be applied to Pima. He said he will be doing additional testing in the field this summer but the project is expected to take several seasons to complete.

Plant mapping has been used the last dozen or so years and consists of writing down on cards data on bolls and fruiting branches, essential for projecting yields, from plants. Calculations from the data assist in decisions for irrigation, crop growth regulators, pest management, and defoliation.

Gathering data

Marsh, who is also director of the Shafter Research and Extension Center, has been working to gather such data with inexpensive, handheld personal digital assistants (PDA) for rapid transfer to spreadsheets generated by office computers.

Part of the work is developing programming to process the data into reports using Bayer CropScience’s ScoutLink. He is using the Scout UCD software to take data collected in the field on first, second, and third position bolls.

Marc Lewkowitz, executive vice president, Supima, said American Pima cotton fiber is gaining prominence in the fast-growing luxury segment of apparel marketing.

"We are consulting on blending our cotton with vicuna wool, which goes for more than $1,000 per pound, with companies such as Chanel and other high-end brand names."

Affluent consumers, he said, are looking to inject luxury into every-day items and are willing to pay a premium for them. Another example is Brooks Brothers, long a user of the Supima brand for its shirts, using the fiber for underwear. Denim blends of Pima with cashmere or angora wool are also finding their way into the blue jean market.

Much of the thrust of the new up-scale marketing trend among retailers is customer retention. Surveys, Lewkowitz said, indicate it is five times more difficult to attract new customers than it is to retain existing customers with appealing, new items.