Potato leafhoppers have now been found in some NH sites – they have likely arrived on recent storms coming from the South. These can cause serious damage on their favorite host crops, so now is the time to scout and manage them, before the damage occurs.
Leafhoppers overwinter in the Southern U.S., and travel north on wind currents. Once they arrive, they begin to feed and breed for the rest of the growing season. Because they don’t overwinter here, crop rotation doesn’t help control them at all.
The adult potato leafhopper is pale green and wedge-shaped, about 1/8 inch long. If you brush plants as you walk by, the leafhoppers will fly up and settle back down. Nymphs can be found on the undersides of leaves. They are even smaller than the adults, and, went disturbed, they move sideways in a crab-like motion. This movement is distinctive of the potato leafhopper. Most of the leafhoppers that are yellowish-green and present on vegetable crops listed below are potato leafhoppers, but there are many other leafhopper species in NH as well. Not all are pests of vegetable crops.
The crops that are most commonly affected by potato leafhopper include potato, bean, strawberry, alfalfa, eggplant, and cantaloupe. The potato leafhopper sucks the juices out of leaves and simultaneously injects a toxin that clogs the vascular tissue of the plant. The leaves first turn yellowish around the margins. This looks a lot like a disease or a nutritional deficiency. After the initial yellowing, the leaves turn brown and curl slightly, and the plants die within a couple of weeks. It looks like the leaves have been burned, hence the term “hopperburn” to describe the damage. If your potato plantings turn brown and die back early, and you were not managing this pest, this is a very likely culprit. While the tubers already produced will not be harmed, this can cause big yield reductions, particularly for later varieties that need a longer growing season.
Among potato varieties, there are dramatic differences is susceptibility to hopperburn (or attractiveness to the potato leafhopper). In an on-farm study by Abby Seaman and her colleagues at Cornell University, the varieties Red Norland, Carola and All Blue stood out as being highly susceptible to hopperburn, whereas Prince Hairy, Yukon Gold, Elba, Russian Banana, and All Red were relatively tolerant. If you do experience damage, it’s worth taking note to see if any varieties seemed much more tolerant to the pest. In our nonreplicated plantings at home, Satina, Keuka Gold, Russett, and Cranberry remained healthy after Red Norland, Superior, Purple Majesty, and Purple Sun were completely killed. Caribe, Rose Finn Apple, and Banana showed intermediate symptoms.
Thresholds for treatment. Because the potato leafhopper causes such severe damage, the thresholds at which controlling the pest is recommended are pretty low (e.g. if you see 15 or more nymphs on the undersides of 50 leaves). Once you see the hopperburn, it is too late to control the leafhopper. There are many insecticides that are labeled for potato leafhopper control; you can refer to the New England Vegetable Pest Management Guide (http://www.nevegetable.org) for details. For certified organic growers, pyrethrum is the most effective option. No matter what material you are using, because the nymphs are on the undersides of the leaves, it’s important to get thorough coverage.
Acknowledgements: A. Seaman et al. ‘Screening potato varieties commonly grown by organic farmers for susceptibility to damage and yield reduction caused by potato leafhopper”, located at: http://www.nysipm.cornell.edu/reports/ann_rpt/AR05/projects/seaman2.pdf , MOFGA Pest Report, June 24 2010.