Factors Affecting Spotted Wilt Incidence and Severity

• History and Location
• Cultivar
• Planting Date
• Plant Population
• Insecticide Use
• Row Pattern
• Tillage
• Herbicides

These factors are listed roughly in order of their importance. Within any given year, there may be huge differences in spotted wilt severity from one area to another, although areas without spotted wilt problems have shrunk dramatically. Cultivar choice has been the most consistent way to suppress spotted wilt epidemics. Typically, use of available moderately resistant cultivars will reduce incidence of spotted wilt by approximately 50% compared to susceptible cultivars such as Florunner or Georgia Runner. Greater reduction may be possible with new cultivars such as DP-1 or Georgia 02C. Planting date is a huge factor virtually every year. However, optimum planting dates vary for a particular year, and shift across years. During the last couple of years, optimum planting date for minimizing spotted wilt has been later than in previous years. The Risk Index has been modified to take that into condideration. Establishment of good plant stands is critical for minimizing spotted wilt incidence and severity regardless of cultivar used. Although most insecticides have little, if any, effect on spotted wilt incidence, use of phorate (Thimet or Phorate) in-furrow at planting has shown consistent suppression of spotted wilt. Row pattern and tillage have also provided consistent suppression of spotted wilt in recent years. Even more recently it has been found that use of Classic herbicide tends to increase severity of spotted wilt. That has been added as a new factor in the Risk Index for 2003.