According to Cornell University Cooperative Extension, "The potato leafhopper (PLH) is a serious pest of vegetable, forage, and fruit crops in the eastern and midwestern United States. The PLH is a sucking insect, removing plant sap
directly from the vascular (water and food transport) system in the leaflet, petioles, and sometimes the stem. In the feeding process, the PLH injects asalivary toxin that causes injury to the plant. Feeding injury sometimes
appears very similar to disease symptoms or nutrient imbalance. By adversely affecting the vascular system, PLH reduces photosynthesis, decreases productivity, stunts the plant, and sometimes kills young seedlings. The salivary substance forms a plug in the vascular system in addition to acting as a phytotoxin. Plant damage is frequently intensified during periods of moisture stress."
In other words, the dry weather isn't helping the potatoes either.
According to Farmer Rob, the leafhoppers are a pest that can be counted on every year to inflict damage, though some years are worse than others. Years ago, Farmer Rob recalls, Howell Farm grew a variety of potato that was more resistant to leafhoppers -- thanks to hairy stems -- and the results were dramatic. That year, the potato crop yielded four times as many potatoes as usual.