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One uncommon problem

This year, three maladies struck in west Tennessee — an uncommon foliar disease, a familiar pathogen and a gamble by some farmers to not use an in-furrow fungicide. Together, they didn't give some cotton plants much of a chance.

Dry weather early in the planting season didn't do much for plant growth, but it meant that the cold, wet weather fungus, Pythium, wasn't much of a problem. In May, warm, wet weather did open the door for the disease that favors those conditions, Rhizoctonia.

The most surprising disease found this year in the region, according to University of Tennessee professor and plant pathologist Melvin Newman, was the foliar disease Ascochyta blight.

“It's in the field all the time,” said Newman, during a recent Seedling Disease Tour sponsored by Uniroyal in Jackson, Tenn. “It's a wet weather blight that will knock the cotyledons off first. If the weather continues to be cloudy and rainy, it will march right up the other leaves.”

The disease starts out on the leaf as a small brownish spot with an ash-white center. Newman says the problem is worse in conventional-till cotton because the fungus is carried on soil splashed onto the leaves during heavy rainfall.

“In no-till, the plant debris keeps the rain from splashing soil. The best preventative I've seen to date for this Ascochyta blight is no-till. There is a huge difference between fields.”

But the biggest problem this year may have been too many farmers rolling the dice and leaving off an in-furrow fungicide.

“Cotton producers have been lulled to sleep over the last three years about using one,” Newman said. “It's a hard sell for producers. They're losing money every day and they want to cut something.”

But according to Newman, cotton producers in west Tennessee won't make it cutting in-furrow fungicide every year. “Fungicides are just a cost of production. It's something you're going to need.”

Newman explained that over a five-year timeframe in west Tennessee, “one year, seedling disease is going to be so bad that you waste your money on a fungicide. There's also a year in five when it's not going to matter — it's going to come up if you plant on a gravel road. But there will be three years that it will pay and one of those years it will pay really well.”

This spring is looking more and more like one of the latter years. “Many cotton producers in the region who used an in-furrow fungicide this year are really glad they did,” the pathologist said.

Newman stressed that fungicides alone don't protect cotton seedlings from everything in Mother Nature's arsenal. One often underestimated consideration is to plant quality seed.

“Find the cold test results of the lot of seed,” Newman said. “Smart farmers are doing that these days. I would be afraid of anything less than 60 on the cold test.

“Another factor is the huge difference in some years between seed treatments and soil treatments. Soil treatments put down many times more active ingredient in the soil and treat the soil around the roots.

“Also, do not use a systemic in-furrow insecticide or a soil-incorporated herbicide without using a soil fungicide. That's been in our recommendations for 25 years.”

Newman's test plots at the experiment station did produce a piece of serendipitous information.

The third row in Newman's planter was inadvertently adjusted to plant a little deeper than the rest. The effect of this was quite obvious in checks, but not where the more efficacious fungicides were used. “That tells us that by planting deeper, we added more stress than we wanted. But the fungicide helped it come on out.”

Newman urged growers to check out research on the various fungicides since there can be big differences in how they perform. “Shop around for a good price. Just remember, in Tennessee, we want the double fungicides, for Pythium and Rhizoctonia.


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