Weather based prediction of spotted wilt in flue-cured tobacco in Georgia
Spotted wilt first appeared in Georgia in 1986. By 1995 tomato spotted wilt virus (TSWV) had become the leading cause of disease loss in Georgia tobacco. Attempts to predict spotted wilt incidence based on winter cold and its assumed influence on mortality of TSWV and its thrips vectors have not been successful. Recent studies of weather influence on thrips abundance in North Carolina have found winter heat units (10.5 C base degree days) and rainfall in March were highly related to catch numbers of tobacco thrips, the principle vector of spotted wilt in tobacco. Historic weather records stored in the Georgia Automated Environmental Monitoring Network were used to create 18 heat unit and rainfall perimeters for each year from 1995 to 2009. This data set was regressed against the mean spotted wilt incidence developing in untreated plants each year in University of Georgia trials conducted for the same time period. Simple correlation found January degree days had the best relationship to annual spotted wilt incidence (R2 = 0.52; pr > f = 0.004). When this variable was plotted versus spotted wilt incidence by year the relationship appeared poor from 1995 to 1998 but very good after 1998. The correlation between January heat units and spotted wilt incidence from 1999, 2009 was better (R2 = 0.63; pr > f = 0.004). A stepwise regression of all variables versus spotted wilt incidence was run. January degree days, mean winter temperature and number of days with rain (>0.04 cm) in March contributed to the model (R2 = 0.90; pr > f = 0.007). The better fit of a weather based model on spotted wilt from 1999 to 2009 as opposed to 1995 to 2009 suggests the range of TSWV was continuing to expand from 1995 to 1998.