Effectiveness of a Point System for Scheduling Foliar Fungicides in Soybean Seed Fields. D. M. TeKrony, Professor, Department of Agronomy, University of Kentucky, Lexington 40546-0091. R. E. Stuckey, Extension Professor, Department of Plant Pathology, and D. B. Egli, Professor, and L. Tomes, Research Technician, Department of Agronomy, University of Kentucky, Lexington 40546-0091. Plant Dis. 69:962-965. Accepted for publication 3 April 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-962.

The effectiveness of a point system developed in Kentucky for predicting seed infection by Phomopsis sp. was evaluated in 1982 in 19 soybean fields covering a wide range of cultural, geographical, and environmental conditions. The point system included cropping history, cultivar maturity, planting date, and rainfall during seed development and maturation. The system accurately identified six fields that should not have been sprayed (8 points or less). Seed infection by Phomopsis sp. for these fields ranged from 0 to 11% (average 5%). The seed infection levels of the five fields for which foliar fungicides were recommended (11 or more points) ranged from 13 to 47% (average 25%). Seed infection levels for fields receiving a marginal rating (9 or 10 points) ranged from 5 to 40%. Measurement of pod infection by Phomopsis sp. at growth stage R6 was useful in identifying fields in this marginal category that had high levels of seed infection. A close relationship (r = 0.86) was shown between pod infection at R6 and seed infection at harvest maturity. This investigation showed that a point system could provide valuable information to soybean seed producers regarding potential seed infection by Phomopsis sp.

Keyword(s): Diaporthe phaseolorum var. sojae, Glycine max.