Insect alert: potato leafhopper decimating some Ontario alfalfa fields

Potato leafhopper damage in alfalfa. C. O’Reilly, 2021

Last week’s insect alert of weevil hitting second-year alfalfa fields has now been expanded to include the potato leafhopper and more acres.

Leafhopper can be especially hard on newly-seeded alfalfa, even if it is a resistant variety. The resistant trait is not expressed in the first growing season, explains Peter Johnson, resident agronomist for RealAgriculture.

The leafhopper is the same species that attacks edible/dry bean fields as well. Tracey Baute, Ontario’s entomologist, says that dry bean fields can be susceptible a few weeks after planting as seed treatment effectiveness begins to wane.

The economic threshold for potato leafhopper control is point-five (0.5) adults in six inch tall alfalfa or two adults or nymphs in 14″ alfalfa; however, Baute adds that if both weevil and leafhopper are present, control may be warranted when either pest is approaching threshold. See more in this article in Field Crop News.

As with weevils, the preferred and best control method is cutting the crop, which saves the cost of spraying and risk to pollinators and natural enemies. However, in heavy infestations, these pests can stick around or in the case of potato leafhopper, adults re-infest fields and cause damage to the early growth of the second crop so scouting is recommended again after first cut, Baute says.

Ontario’s Agronomy Guide also has more information on pages 341-342.

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