Peanut disease control changed drastically

The face of peanut disease control has changed drastically over the past 20 years, from strict calendar schedules for spraying to new prescription programs, and from only one or two varieties to several, some with their own disease resistance packages.

“We’ve seen a lot of changes in peanut disease management over the years,” says Bob Kemerait, University of Georgia Extension plant pathologist. “Twenty years ago, we didn’t know what tomato spotted wilt virus was, and we planted mostly Florunner.”

Control options, he says, were limited for leaf spot, white mold, CBR and other peanut diseases. “For leaf spot control, if you wanted a resistant variety, you planted Southern Runner, but mostly we planted Florunner. We basically had one material for leaf spot and that was Bravo or chlorothalonil. For white mold, we had crop rotation and Lorsban, and for CBR, we had Vapam or metam sodium. Nematode control hasn’t changed that much, with Telone and Temik. The bottom line is that we now have many, many more options for peanut disease control than we did 20 years ago,” says Kemerait.

The question now, he says, is not what our options are, but how do we use them?

“In 2010, variety selection is critical. We have varieties with excellent resistance to white mold, CBR, leaf spot and nematodes. We now know the influence of factors such as planting dates and twin rows on disease.

“We also have Peanut Rx or prescription fungicide programs. In 1990, growers were told to spray seven times, starting 30 days after planting and no later than June 1, staying on a 14-day schedule. We can still do that effectively, but that’s not the only program we can use. We have more nematicides and a better choice of fungicides. It has gotten more complicated, and one of my jobs and the job of Cooperative Extension is to help you make decisions that will make more money from your crop, and that depends on the program you use,” he says.

Many growers, says Kemerait, are probably wondering what they’ll spray in 2010. “As long as you use a good fungicide program, stay on time with your sprays and use the right rates, those programs are more alike than they are different. But you can still run into problems. If disease pressure is low, there’s no problem. But if you get into high disease pressure, growers will likely benefit from fungicide programs that incorporate the best products, he says.

It’s clear from looking at peanut yield trends, says Kemerait, that progress is being made with new chemistries and varieties. This past year, Georgia’s average yield was a record 3,500 pounds per acre.

“We are turning the corner on tomato spotted wilt virus, and we’re turning the corner on diseases — it’s a combination of varieties and good disease management programs,” he says.

Turning to seedling disease in peanuts, Kemerait says it’s estimated that over time, a grower who doesn’t have a disease treatment on his peanuts can lose at least 900 pounds per acre. “On a plot with a high soil temperature and without a seed treatment, we saw a loss of 2,000 pounds per acre. When you’re talking about how expensive a fungicide program is going to be, and how you don’t know which to choose, the good news is that when you put the treated seed in the ground, you’ve already invested in one of the best values you’re going to get. That’s the good news, and you don’t even have to think about it because it’s on the seed — that a tremendous value for you.”

As for fungicide spray programs, many growers still use the old standard successfully, notes Kemerait.

“But we’ve worked on developing prescription fungicide programs for Peanut Rx. It’s all about putting the right amount of fungicides on your field depending on the risk. If you’re high-risk perhaps because of short rotations and planting less-resistant varieties, you need to spray at least seven times — in a year like 2009, maybe eight or nine times.

“But if you have good rotation, good varieties, and good management, you might get away with four or five sprays. The important thing is that the prescription program is a tangible way for growers to benefit from using good management.”

Peanut Rx is now endorsed by several fungicide manufacturers, he adds, who work with growers to reduce their sprays if they’re using good management practices.

All varieties now typically have improved resistance to tomato spotted wilt virus, says Kemerait, and also resistance to leaf spot. “When I began in my job, you started your fungicide spray program no later than 30 days after planting or June 1. Now we have programs that we don’t kick off until 45 days after planting. We’ve got products on the market with good systemic activity, so we can now base our disease management not only on the planting date but also on the efficacy of the chemistry.”

Systemic fungicides have changed how growers manage diseases, he says, because these materials can get into the leaf of the plant.

Leaf spot disease was very aggressive this past year, and as a result, there were some control failures, says Kemerait. “Wet weather was prevalent, and typically, growers would not compensate for that extreme wet weather by tightening their spraying. That’s when we saw some failures of leaf spot programs.”

Because of resistance concerns associated with the use of tebuconazole, or Folicur, growers need to tank-mix it with another material when using it, he says. “This was probably the single most commonly used fungicide in peanut fields last year, the single most commonly used fungicide on soybeans, and it also was commonly used on corn. It’s a good fungicide, and it’s cheap. But when it comes to any of those crops, tebuconazole is not the best fungicide on anything. It’s not the best leaf spot material for peanuts by far, and it’s not the best CBR, white mold or limb rot material. Tebuconazole is a good product, but it’s not the BEST product.”

“If you have disease problems, or you anticipate or want to avoid problems, you need to weigh the cost of a cheaper fungicide versus the efficacy of a premium fungicide,” says Kemerait.

Another advancement in peanut disease control in recent years has been night spraying, he says. “It’s so simple, but a lot of us never would have thought of it. Peanut plants close up at night, and you can get the fungicide down into the crown of the plant to control limb rot and white mold.”

According to University of Georgia research, it is in the realm of possibility to increase yield by 1,000 pounds per acre simply by changing the timing of the fungicide application.

If you have it in your field, says Kemerait, CBR can be your No. 1 control problem. Until recently, fumigating with Vapam or metam sodium was the standard, especially in the Carolina/Virginia region. A more recent option, he says, is Proline applied in-furrow followed by Provost or some other material labeled to suppress CBR.

Root-knot nematodes, says Kemerait, continue to be an issue for peanut growers, especially those with sandy soils. In 1990, the options for control included Telone and Temik, and it 2010, the options still include Telone and Temik, along with some biological products. In addition, the variety Tifguard has resistance to root-knot nematodes.

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TAGS: Peanuts
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