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Growers more aware of nematodes

Nematodes continue to cost cotton producers more in chemical control, direct damage and indirect losses than any other plant disease. And, considering that some species of nematodes were here before the time of dinosaurs, it isn't likely they're going away anytime soon.

The good news is that growers are becoming more aware of the nematode problem, and they're doing something about it. “Growers definitely have become more aware of the threat from nematodes,” says Bob Kemerait, University of Georgia Extension plant pathologist. There has been a push in recent years by Extension and others in the industry, he says, to make growers more aware of the potential damage from nematodes and to give them options for controlling the pest.

In 2004, nematodes caused the loss of an estimated $402 million — more than one million bales of U.S. cotton.

The introduction of a new product, of course, always helps to spur interest, and that has been the case this year with Syngenta's Avicta CompletePak. From an educational standpoint, the new nematode control product and its advertising campaign have done a service to U.S. cotton growers in by raising the consciousness of nematodes in their fields, says Kemerait.

However, he urges growers to do their homework to make the best decision when selecting a nematicide for their fields.

Kemerait, has looked at Avicta in more than a dozen field trials over the past three years,

“In our trials at the University of Georgia in 2004 and 2005, yields from plots treated with Avicta CompletePak were typically not statistically different from 5 pounds per acre of Temik. In about 50 percent of these trials, Avicta CompletePak numerically out-yielded Temik, and in a little over 50 percent of the trials, Temik numerically out-yielded Avicta. However, where Temik out-yielded Avicta, the yield advantage to Temik was typically greater than when Avicta out-yielded Temik. Though again, differences were often not statistically different,” he says.

Although the field trials in 2004 and 2005 were conducted in “nematode” fields, there wasn't a significant difference between the Avicta and the Cruiser yields, adds Kemerait.

Growers who have a severe problem with nematodes in at least some of their fields should use products like Telone II or perhaps Temik at planting and side-dress to effectively manage the problem, he advises. “For such fields, I do not recommend the use of Avicta, at least as a ‘stand alone’ product,” he says.

For growers with low-to-moderate levels of nematodes, Avicta CompletePak may be an option they'll want to consider, says Kemerait. “If a grower chooses to use Avicta CompletePak in a field with low-to moderate nematode pressure, I would recommend that they include side-by-side comparisons with their standard treatment, such as Temik at 5 pounds per acre. I do not recommend that a grower switch completely from Temik to Avicta — we still have much to learn.”

Growers need to remember, says Kemerait, that the new product is, at best, as good as 5 pounds per acre of Temik. “There is no need to rush to change completely from a practice that has been effective in the past. The 2006 season will be a great test for Avicta. If the product stands up to the ‘nematode test,’ more growers will adopt the practice in the future. However, if Avicta does not perform as advertised over a wide range of fields, cautious growers in the 2006 season may end up as the real winners,” he says.

Avicta CompletePak does contain Dynasty as one of its components, he says. And although the addition of this fungicide certainly won't hurt, no yield advantage has been seen for Georgia's cotton growers where fungicide “overcoats” are used in addition to the standard fungicide seed treatment package already applied to the seed, says Kemerait.

Researchers in Alabama also have been comparing treatments of Avicta CompletePak, Cruiser and Temik for the control of nematodes.

“If you're in a situation with high reniform nematode populations, and you're trying to decide between Temik and Evicta, we're still recommending Temik. If you're in a moderate or low nematode situation, we think Avicta may work fine,” says Dale Monks, Auburn University Extension cotton specialists.

In 2005, nine on-farm reniform nematode trials were conducted in northern and central Alabama. Three treatments each of Temik, Cruiser and Avicta were replicated three times across the field. Temik was applied in-furrow at 5 pounds per acre except for one site which received 7 pounds. Cruiser and Avicta both were seed treatments.

Soil samples for evaluating Temik degradation also were collected at planting, and early season thrips counts were made from all plots.

Vydate at 17 ounces per acre was over-sprayed on each test during squaring. Nematode levels were monitored throughout the season, and yields were determined by picking the entire plot area and weighing on a boll buggy.

Reniform nematode numbers varied greatly between samplings. In fact, nematode variability was so great that in most cases, differences in nematode populations due to treatments were not statistically significant. This data demonstrates, say researchers, the difficulty in establishing critical nematode threshold levels for control recommendations. Researchers had hoped to use pre-season nematode soil samples as a tool to rate fields. However, two of the fields had very high reniform levels prior to planting, at 10,000 and 20,000 per plant. Then, populations dropped to 5,000 per plant at planting. In two other fields, preplant reniform nematode levels were 5,000 to 7,000 per plant but jumped to about 20,000 at planting, showing a wide fluctuation.

Two of the test sites had very low yields, one due to extremely dry weather and a month's delay in getting a stand. Another of the fields cut out shortly after Hurricane Katrina and did not develop a top crop.


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