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Forages & Grains
Volume 59 Number 8 Date 06/19/2014 ALFALFA WEEVIL - Larval counts in southern and central Wisconsin have declined due to pupation and harvest of first-crop alfalfa. Carryover of larvae into second-crop regrowth is common, although averages are below one per sweep and leaf tip damage is generally less than 20%. Most weevils are in the third and fourth-instar stages and should pupate within the next two weeks. Routine scouting is suggested through early July or until the weevil season has passed. PLANT BUG - Alfalfa fields as far north as Chippewa County are showing low populations of 0-1.3 per sweep. The economic threshold is five per sweep. Nymphs are still more abundant than adults in most fields. MEADOW SPITTLEBUG - The first spittle masses appeared three weeks ago and late-instar nymphs are now the predominant development stage. Adult spittlebugs should begin appearing in alfalfa sweep net collections by July. A population of 1.0 or more nymphs per stem may interfere with harvest operations, but infestations of this level are rare in Wisconsin. -- Krista Hamilton, DATCP Entomologist POTATO LEAFHOPPER - Populations are approaching the economic threshold of 1.0 per sweep in some 8- to 11-inch alfalfa fields. Counts for the period of June 12-18 varied from 0-0.6 per sweep, with the highest average (30 per 50 sweeps) found in Monroe County. Nymphs, which can be an indicator of population increase, were swept from two of the 47 fields sampled. 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. PEA APHID - Counts have not changed significantly since the last report. Averages in 47 alfalfa fields surveyed from Walworth to Dunn County ranged from 0.5-7.6 per sweep, which is normal for this time of year. The highest counts were observed near Hazel Green in Grant County. Pea aphid populations in Wisconsin alfalfa usually peak by mid-June and then decline in July. -- Tracy Schilder, DATCP Plant Pest & Disease Specialist 
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