Losses to tomato spotted wilt across the Southeast were among the lowest recorded since estimates began in 1990. It is estimated that losses associated with spotted wilt were about one percent last season. It is believed that growers were able to achieve excellent management of this disease in large part through combined use of Peanut Rx and varieties with improved resistance.

The Spotted Wilt Index and the Peanut Fungal Disease Risk Index were combined in 2005 to produce the Peanut Disease Risk Index. The index, developed by researchers and Extension specialists at the University of Georgia, University of Florida and Auburn University, is now known as Peanut Rx. The 2009 version has been fully reviewed and updated based on observations from the 2008 season.

Changes that have been made to the 2009 Peanut Rx can be found in the cultivar/variety section and in commentary regarding the relationship between use of Classic herbicide and the incidence of tomato spotted wilt, which follows.

Change To Classic Comments
Research and field observations over the past several years have confirmed that the use of Classic (chlorimuron) can occasionally result in an increased expression of tomato spotted wilt of peanut. Classic caused an eight percent or less increase in tomato spotted wilt about 78 percent of the time, and an increase of more than eight percent about 22 percent of the time. These results indicate that the effects of Classic on TSWV are minimal in comparison to the other production practices that influence this disease.

Consequently, late-season Florida beggarweed populations that have the potential to reduce harvest efficiency and fungicide spray deposition should be treated with Classic. To date, other peanut herbicides have not been shown to have an influence on spotted wilt.

Assess Your Risk Level
For each of the factors that can influence the incidence of tomato spotted wilt or fungal diseases, identify the option that best describes the situation for an individual peanut field. An option must be selected for each risk factor unless the information is reported as “unknown.” A score of zero for any variable does not imply “no risk,” but that this practice does not increase the risk of disease as compared to the alternative.

Add the index numbers associated with each choice to obtain an overall risk index value. Compare that number to the risk scale provided and identify the projected level of risk.

For a complete listing of the varieties and point values and to read comments associated with many of the factors that affect tomato spotted wilt and fungal disease, go to the UGA Web site at www.ugapeanuts.com, and click on 2009 Peanut Update and then on 2009 Peanut Rx.

A Few Notes About Risk Levels
For spotted wilt, a point total greater than or equal to 115 indicates high risk; 70 to 110 indicates medium risk; and an index total less than or equal to 65 indicates low risk. If a low-level risk is predicted, it is expected that the field would be less likely to suffer major losses due to TSWV than a field rated for a higher level of risk. However, it does not imply that a field is immune from TSWV losses. In a year when TSWV incidence is high statewide, even fields with a low-risk level may experience significant losses.

For leaf spot, a point total of 65 to 100 indicates high risk; 40 to 60 indicates medium risk; and 10 to 35 low risk.

For white mold, a point total of 55 to 80 indicates high risk; 30 to 50 indicates medium risk; 15 to 25 offers low risk. For Rhizoctonia limb rot, a point total of 45 to 75 indicated high risk; 30 to 40 indicates medium risk; 15 to 25 indicates low risk.

It should be noted, when weather conditions are favorable for fungal diseases, especially when rainfall is abundant, even fields at initial “low risk” to fungal diseases may become “high risk.” If high risk is indicated, growers should use a full fungicide input program.

For medium-risk fields, growers can expect better performance from standard fungicide programs. Reduced-fungicide programs in research studies have been successfully implemented when conditions are not favorable for disease spread.

For low-risk fields, growers have made management decisions that offer maximum benefit for reducing the potential for severe disease. These fields are strong candidates for modified disease management programs with a reduced number of fungicide applications.

PG