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Average year for seedling disease in Tennessee

Seedling disease pressure in west Tennessee cotton fields could have been a lot worse this year, considering the really ugly weather early on.

“But the cotton came through all right,” said University of Tennessee plant pathologist Melvin Newman, who says this year’s yield loss to seedling disease in west Tennessee is about average compared to most years.

One reason, “a lot of seed treatments were used and some in-furrow treatments went out too.”

West Tennessee cotton typically has the highest loss to seeding disease in the Cotton Belt, with an average annual yield loss of 10 percent, according to Newman. Losses to seeding disease, primarily to Rhizoctonia and Pythium, in 2002 and 2003 were over 20 percent. The percentage dropped to 8 percent in 2004 and 4 percent in 2005.

The trend toward the use of fungicide seed treatments is rising in west Tennessee, although some growers still use in-furrow fungicides. “Farmers are learning what they can get by with and what they can’t get by with. The best thing to do is put fungicide in the soil, but it adds expense and it adds time.”

Newman doesn’t blame producers looking to lighten their load during planting and going with seed treatments only, “when you look at some of the equipment that producers have, 12 or more rows of planters that they have to fold up.”

But he still prefers that west Tennessee producers use an in-furrow treatment “especially in our west Tennessee bottoms and under certain conditions.”

Newman’s annual seedling disease test plots indicated “a lot of difference between seed treatments and in-furrow treatments in 2006. We did have fairly severe conditions. We planted early in April. You can pick out the in-furrow treatments from a good ways off. They’re showing an increase in size and vigor versus the seed treatment.

“So I still hold to what the data shows, that under heavy disease pressure, you need more fungicide than what’s on the seed. But I do give seed treatments credit for having come a long way over the last few years.”

Newman continues to work with University of Tennessee agricultural engineers on a seed-specific fungicide applicator, which could cut costs for growers who prefer using an in-furrow fungicide.

The concept of seed-specific applications grew from Newman’s observation that only the fungicide sprayed directly into the soil around the seed was needed. “Currently we’re putting down too much and seed-specific placement could result in significant savings. Environmental benefits are there too. Other chemicals that are placed in-furrow could also show savings from the technology.”

The technology uses optical sensing to calculate the speed of the seed and the planter moving through the field. A high speed valve sprays the fungicide on the seed after it drops into the furrow. “It not only covers the soil, but it covers the seed, too.”

Research indicates no statistical difference in stand development and yield between an in-furrow fungicide application applied continuously versus a seed specific application.

Research also indicates the benefit decreases as seeds per foot increases. For example, the cost of a seed-specific application at 8 seeds per foot was not different from a continuous in-furrow spray, at $15.04 per acre. At a seeding rate of 3 seed per foot, the fungicide savings were $7.52 per acre, according to Newman.

The technology is not yet available commercially, according to Newman. “But we are looking for someone to step forward and develop the technology. I think it’s worth it.”

This season, soybeans took a harder hit than usual from disease, according to Newman. “We’re still having problems (early July) with phytophthora root rot. A few fields had to be replanted. Some of those fields had 4-inch to 6-inch soybeans which were affected.”

Tennessee does not have widespread adoption of the early soybean production program. In fact, “due to resistant horseweed in west Tennessee, I saw a lot of late planting of soybeans this year,” Newman said. “A lot of no-till growers were letting the horseweed get pretty tall and then disking up their land.”

Heavy rains were to blame for most of the problem, according to Newman. The disease affected plants where “water just wanted to puddle a little bit. It didn’t take much, even on well-drained land. And our no-till land held water even more. It provided the ideal environment for disease. But I think the danger is now over and I don’t think we’ll see any more plants die.”

The prevalence of the disease this season could give soybean producers an incentive to use a seed treatment on their soybeans in the future, Newman said.


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