3.1.22
DEVELOPMENT AND VALIDATION OF AN INTEGRATED MANAGEMENT SYSTEM FOR SPOTTED WILT DISEASE IN PEANUT IN GEORGlA

JW TODD1, AK CULBREATH2, DW GORBET3, FM SHOKES4, SL BROWN1 and HR PAPPU2

1Department of Entomology, and 2Department of Plant Pathology, University of Georgia, PO Box 748, Tifton, GA 31793-0748, USA; 3Department of Crop and Soil Sciences, North Florida Research and Education Center, Marianna, FL 32446, USA; 4Department of Plant Pathology, North Florida Research and Education Center, Quincy, FL 32351-9500, USA

Background and obiectives
Spotted wilt disease, caused by tomato spotted wilt tospovirus TSWV), has become a major yield- and profit-limiting factor on numerous agronomic and horticultural crops worldwide [1]. Spotted wilt was first observed in the southern USA in the early 1980s, with most recent incidence levels as high as 70-90% in peanut, pepper, tomato and tobacco. In 1995, spotted wilt became the most damaging disease problem in peanut in Georgia and Florida and caused an estimated loss of over $33 million in Georgia alone. Similar losses in peanut were sustained in 1996 and 1997. Recent research has shown that although no single practice provided adequate suppression of TSWV in peanut (2], various combinations of cultural practices have significantly reduced incidence, severity and yield losses resulting from spotted wilt. We used those results to develop an integrated management system and a 'risk assessment index' for spotted wilt in peanut which includes the following components: (i) use a 'resistant' cultivar; (ii) avoid very early and very late planting dates; (iii) plant to achieve a stand of ca 4 plants per 30 cm of row; and (iv) use of Thimet insecticide at planting (except where other problems dictate otherwise) (3].

Mateterials and methods
Extensve validation research and 'on-farm' surveys conducted in 1996 and in 1997 confirmed the utility of the package approach set forth in the UGA TSWV Risk Index [3]. The effects of final spotted wilt severity on peanut yield were determined where the various combinations of cultivar, planting date, plant population, and systemic insecticide at planting were established. Those results were used as the basis for revisions of the Index in 1996 and again in 1997.

Results and conclusions
Final spotted wilt severity ranged from 12.8 to 61.6% of each 30.17 m of row severely affected in the early planted tests, and from 10.1 to 46.6% in the mid-(optimum) planting date tests among the combinations of practices. Yield was highly correlated with final spotted wilt severity and when data were pooled from three locations in the early and mid-planting date tests, correlation coefficients of R=0.87 (early) and R=0.84 (mid-) were achieved. Peanut yields were reduced ca 280.2 kg/ha for each 10% increase in TSWV final severity. Cultivar selection proved to be the most important factor, with planting date, plant populations, and insecticide contributing less, but still giving significant additional reductions in TSWV and resulting in higher yields. Differential risk index values calculated for each of the treatment combinations also correlated well with TSWV severity (R=0.90) and yield (R=0.81). On-farm surveys of various combinations of practices adopted by farmers gave similar results in reducing TSWV severity. Correlations of TSWV and risk index values with yield gave lower R-values in on-farm observations due to the myriad of other yield-reducing factors encountered. These results lend substantial experimental support for this integrated multifactorial management system to address the TSWV problem and the utility of the risk assessment index as a delivery and educational vehicle. Adoption of the Index by peanut growers met expectations in 1996 and exceeded forecasts in 1997.

References
1. Cho JJ, Mau RFL, German TL et al., 1989. Plant Dis. 73, 375-383.
2. Culbreath AK, Todd JW, Demski JW, Chamberlin JR, 1992. Phytopath. 82, 766-771.
3. Brown S, Todd J, Culbreath A, et al., 1998. Univ. of GA, Ext. Bull. No.1165, 12 pp.