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Forages & Grains
Volume 64 Number 8 Date 06/20/2019


ALFALFA WEEVIL - The peak larval damage period is expected to end by late June as populations reach the non-feeding pupal stage. Weevil numbers have been low this spring. The average count in 210 first-crop alfalfa fields sampled from May 31-June 19 was just 0.4 per sweep (40 per 100 sweeps) and leaf tip feeding was less than 20% in all surveyed fields.

POTATO LEAFHOPPER - Counts in 10-14 inch alfalfa regrowth have exceeded the economic threshold of 2.0 per sweep in a few southwestern Wisconsin fields. Surveys for the period of June 13-19 found averages varying from 0.4-2.2 per sweep, with the highest count (220 per 100 sweeps) observed in Grant County. Nymphs, which can be an indicator of population increase, should begin appearing next week. The neon green nymphs quickly move sideways when disturbed, differentiating them from plant bugs, aphids and other small, bright green insects that collect in sweep nets.

MEADOW SPITTLEBUG - The adult stage of this insect is appearing in alfalfa sweep net samples, signaling that the population has matured. Meadow spittlebug damage is rare but occasionally occurs on first-year alfalfa seeded into small grain stubble. This insect has a single generation per year in Wisconsin, and the risk of damage ends once the adults emerge.

PEA APHID - This insect continues to be the most abundant alfalfa pest. Densities currently range from 1-14 per sweep and average three per sweep. Rainy, humid weather promotes the spread of fungal pathogens that regulate these aphids and often cause populations to collapse by late June.

-- Krista Hamilton, DATCP Entomologist