Forecasting of early blight on tomatoes for more efficent chemical control

The forecasting system for Alternaria solani on tomatoes (FAST) was employed to determine if more efficient chemical control of early blight could be obtained on staked tomatoes in Tennessee. A comparison of three spray regimens based on the FAST method was made with the spray program currently recommended by the University of Tennessee Agricultural Cooperative Extension Service. The combination of two forecasting models based on: the daily ambient temperature, rainfall, the daily period of relative humidity greater than 90%, the daily leaf wetness period, and the ambient temperature during the leaf wetness period, was used to determine an efficient spray schedule. Counts of air-borne conidia of Alternaria solani were also made for comparison to the timing of disease outbreak and increase. During 1980 the best early blight control was achieved by the use of the recommended 5-day spray interval method (26 sprays). Disease control by the 7-day interval method (18 sprays) was significantly less efficient, but not different in disease controlling ability from that of two of the FAST-generated spray regimens (17 and 5 sprays, respectively). However, during 1983 the most frequently sprayed FAST-generated regimen (18 sprays) did provide disease control significantly greater than control by the 5- and 7-day spray interval methods (22 and 19 sprays, respectively), and a less often sprayed FAST-generated spray regimen (15 sprays). \\ith a modification of the environmental requirements which designate the spray schedule to better fit favorable conditions for disease outbreak, improved control could be possible. The quantities of air-borne conidia can help determine the timing for initial spray applications, but not subsequent sprays.