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Risk index helps in managing peanut diseases

Peanut diseases cost Georgia growers millions of dollars in losses each year, not to mention the other millions of dollars required to prevent and control them. But a new fungal disease risk index created by University of Georgia scientists aims to help growers reduce or at least minimize these losses.

The Risk Index for Fungal Diseases of Peanut in Georgia — unveiled for the first time this year in grower meetings — is based upon a better understanding of factors that affect the incidence and severity of diseases, says Extension Plant Pathologist Bob Kemerait.

"With the release of new peanut varieties — coupled with research and knowledge of the impact of factors such as crop rotation, tillage and irrigation on peanut diseases — we felt it was critical to get this information to growers, and to help them understand the relative importance of each factor," says Kemerait. "This will enable them to take steps, whenever possible, to reduce the risk of disease in their fields."

The great success of the University’s tomato spotted wilt virus risk index gave researchers an excellent model for the fungal disease risk index, he adds. "We hope growers can use this index to better manage their crops in terms of less disease, higher yields and better profits."

The index, explains Kemerait, is based on a number of factors that can influence the risk of fungal diseases in a peanut crop. These factors include the variety planted, crop rotation, field history of disease, row pattern, planting date and irrigation.

But these factors, he continues, affect the risk of disease to differing degrees. "For example, the variety planted and crop rotation in a field will have greater impact on risk than perhaps row spacing and planting date. Therefore, the points in the index are ‘weighted’ — based upon research and experience — to reflect this."

In addition, he says, the risk to soilborne diseases such as white mold and Rhizoctonia limb rot from these factors may be different than the risk to leafspot.

"For example, twin rows are better for white mold and spotted wilt but not for leafspot. Therefore, in using the index, growers should assess risk to leafspot and soilborne diseases independently."

Growers can total up the points from each category and determine their risk at the beginning of the season, says Kemerait. "They will be in either a high, middle or low-risk situation. At the very least, having an idea of their risk will help them to keep a closer eye on the crop during the growing season. Using the risk index also may allow them to modify some production practices to reduce their overall risk. Future research may help them to better tailor their fungicide programs to specific levels of risk."

The most effective way to use the index, he says, is prior to the growing season. By doing this, growers will be able to better manage their crops during the season by altering production practices. Or, armed with an idea of the risk, growers can watch for a particular disease.

The index also can be used at anytime during the season to better understand the potential risk to disease, he adds.

The fungal disease risk index is an exceptional educational tool for peanut producers, says Kemerait.

"For many years, we have been preaching about the benefits of disease resistance in new varieties and the benefits of other practices such as crop rotation and tillage. The index allows growers to better understand how these factors are interrelated, and how they can be used to the grower’s advantage. Secondly, the index may help growers to modify their practices to maximize the control of fungal diseases."

In the future, the index may allow growers to adopt improved fungicide programs, says Kemerait. "In some situations, where growers have a very low-risk situation. it is very likely that they’ll be able to reduce the overall cost of a fungicide program by selecting materials and timing applications only when they are needed."

In high-risk situations, he says, growers may find that a more expensive "Cadillac" program will produce the best benefits in terms of yield, grade and profit.

"Our current goal is to develop schemes for fungicide programs based upon the risk that a grower is likely to face. If such a scheme involves fewer fungicide applications in a low-risk situation, such a program will not come at the expense of yield."

The index will be evaluated each year in research and on-farm trials and modified according to the results, says Kemerait. "Growers should know that we’re very serious about the validity of this work, and the impact it’ll have on disease management."

As growers use the index, he advises that they be mindful of the critical role weather plays in the incidence and severity of diseases.

"Even fields that begin the season with very low risk for disease may be affected greatly if the growing season is a wet one."


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