Yield loss of sweet corn cultivars in response to defoliation and to infection byexserohilum turcicum

The effect of northern leaf blight (NLB) or leaf defoliation on the yield of nine sweet corn cultivars was studied in field experiments. Plants were defoliated or infected in the bottom, middle or top third of the leaf canopy. The effect of defoliation or infection on yield was significantly higher for plants treated 55 days after planting than for those treated 70 days after planting. Cultivar response differed significantly for both treatments, the most sensitive cultivar being ‘Jubilee’ and the least sensitive being Ssupersweet 7900. In all cases, the highest yield loss was recorded when the middle third of the leaf canopy was treated. The relative importance of the top third of the leaf canopy increased if the treatment was done 3 weeks before harvesting. This study emphasized the importance of leaf position, cultivar, and plant growth stage for evaluating losses caused by NLB, and may explain the failure of various models to describe yield loss due to NLB.