Variation in tolerance and resistance to the leafhopper Empoasca fabae (Hemiptera: Cicadellidae) among potato cultivars: implications for action thresholds.

The potato leafhopper, Empoasca fabae (Harris) (Hemiptera: Cicadellidae), is an emerging pest of potato and insecticide applications to control this insect have increased in recent years. Based on field observations of leafhopper-crop dynamics, however, currently recommended action thresholds seem to be overly conservative. As a result, we initiated two experiments designed to quantify the impact of leafhoppers on potato yield, and determine how the magnitude of this effect changes among cultivars. In experiment 1, leafhoppers were manipulated (control versus insecticide-treated plots) on 17 potato varieties. In experiment 2, three cultivars (Superior, Atlantic, and Snowden) were planted representing early-, mid-, and late-season maturing lines, and six insecticide spray regimes were imposed (early-, late-, and full-season applications at high and low rates). In both experiments, leafhopper abundance, plant damage, and potato yield were measured. Overall, leafhoppers reduced yield in control plots by 15.7% relative to insecticide-treated plots. Leafhopper impact, however, varied among cultivars; a significant effect of leafhoppers on yield was detected in 6, 12, and 59% of cultivars tested in each of three trials. Of the 44 cases in which leafhoppers exceeded action thresholds, yield loss was only documented in 13 cases. Data from these experiments provide evidence that such variable effects ofleafhoppers on yield are explained by cultivar-specific resistance and tolerance traits. Our results suggest that potato growers can accept higher leafhopper densities than current thresholds recommend, particularly when cultivating resistant and/or tolerant varieties.