Extension budgets list the typical cost of fungicides in peanuts at $70 to $85 per acre — the highest input in peanut production. All the more reason, say University of Georgia experts, for growers to look for new ways of cutting disease control costs.
“Peanut producers in Georgia traditionally put all that's needed into their crops. They don't believe in cutting many corners,” says Bob Kemerait, Extension plant pathologist. “They believe a seven-spray program is the only way to go on fungicides.”
But the reality of the situation, he adds, is that the government support price for peanuts has dropped from $610 to $355 per acre, and growers need to find a way of maintaining good fungicide programs while cutting costs.
Peanut fungicide programs will change in the future based on several factors, says Kemerait. “But one thing that won't change for Georgia growers is disease pressure. If anything, it'll get worse, and we'll continue to see a constant threat from diseases such as leafspot, rust, white mold, rhizoctonia limb rot, CBR and tomato spotted wilt virus. You'll deal with most of these every time you plant seeds to grow peanuts,” he says.
Growers also won't be able to wean themselves from making multiple applications of fungicides, he continues.
“We've never had better fungicides for growing peanuts — they're outstanding. But we need to figure out how to use them more effectively.”
One factor that might change disease management options is a more thorough knowledge of the pathogen that causes a disease, says Kemerait.
“For example, if we know more about the fungus that causes leafspot, we can improve our practices for controlling the disease. These practices may include planting varieties with greater resistance and using more selective fungicides. When you understand more about the biology of a disease, you can do a better job of managing it.”
It's also important to understand, says Kemerait, that not all fields are created equal. “A typical seven-spray program may be exactly what you need for one field, but it might not be enough for another. And, for a field with a good rotation, a seven-spray program may be more than you'll need.”
New fungicides also will drive changes in disease control programs, he says. “We have new selective fungicides and products with systemic activity. The systemic materials are absorbed into the plant to give us better curative activity. These new products also are very specific in the activity they have against pathogens, and they can be used at low rates.”
New products for 2003, he says, include Arson, which is similar in activity to Moncut or Montero; Echo, which is similar to Tilt/Bravo; and Headline, which is from the same class of chemistry as Abound.
“Headline offers excellent control of leafspot disease and rust. It has good curative activity, which means that it can be sprayed on to cure an infection that has occurred fairly recently. In research trials, there was no incidence in disease severity when Headline was applied at 58 days after planting versus 30 or 44 days.
“I'm not suggesting that you wait 60 days before starting your leafspot program. But this new chemistry will allow us to space out our spray intervals, resulting in more activity from fewer applications over the course of a growing season.”
New peanut varieties also are driving changes in fungicide programs, says Kemerait. “Some of the new varieties not only are resistant to tomato spotted wilt virus, but they also have increased resistance to diseases such as leafspot, white mold or limb rot and CBR.
Any new variety releases will have resistance to tomato spotted wilt virus that is equal to or greater than Georgia Green, he says.
New disease-resistant varieties from the University of Georgia breeding program include GA-01R and GA-02C, he says, with GA-02C offering resistance to tomato spotted wilt virus and CBR. DP-1, released by the University of Florida and marketed by Damascus Peanut Company, has excellent leafspot and tomato spotted wilt virus resistance. Other University of Florida releases include Norden, Carver and Hull — all offering differing levels of resistance to leafspot and tomato spotted wilt virus.
In research conducted in Georgia farmers' fields this past year, there was no significant difference in yields or disease incidence when the number of fungicide sprays were reduced in plots planted in DP-1, reports Kemerait. In one case, the resistance in DP-1 allowed the farmer to go through an entire season with only one fungicide application for controlling leafspot, he says.
“Even more important is that the value of the final crop was more when farmers used a reduced program of four fungicide sprays. Farmers received a greater return on their investment. Even if you don't reduce your fungicide program, you should get more yield from these new varieties because of their increased disease resistance.”
Conservation-tillage also has become a factor in disease control strategies, he says. Research in recent years has revealed that conservation-tillage peanut fields have less leafspot disease pressure than conventional-tillage fields.
“It's no secret that you have significantly less tomato spotted wilt virus in conservation-tillage peanut fields than in conventional fields. We're also seeing less incidence of leafspot in conservation-tillage situations. This doesn't mean you should stop spraying if you're planting in conservation-tillage, but you may get more from your fungicide program.”
“All of these factors affect the severity of peanut diseases — varieties, fungicides, field history, crop rotation and the use of disease resistant varieties. These factors can be used to help you make better decisions about controlling disease.”
The University of Georgia is in the process, says Kemerait, of developing a risk index for peanut diseases caused by fungi. The index will be similar in design to the successful Tomato Spotted Wilt Virus Risk Index, he says. Look for the index in a future issue of Southeast Farm Press.
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