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Forages & Grains
Volume 57 Number 5 Date 05/10/2012 ALFALFA WEEVIL - Larval populations have continued to build under the wet weather pattern of the past two weeks. Numbers in the south-central area now range from 2-16 per sweep, with an average of 4 per sweep. Lower counts of 1-3 per sweep can be found in the east-central and west-central districts. Leaf tip damage is generally less than 30%, although a few exceptional fields in Dane, Green and Rock counties have economic defoliation levels of 40-80%. Larvae in the second and third instars are the predominant development stages. Damage will intensify as more larvae enter the larger and most destructive third and fourth-instar stages. First crop alfalfa that is not harvested by mid-May could be degraded to the point that quality and yield have been seriously compromised. Control is suggested when the economic threshold of 40% tip feeding is exceeded more than 7-10 days in advance of harvest. POTATO LEAFHOPPER - Migrants were collected from 19 of 29 alfalfa fields sampled this week, as far north as Monroe County. A report from Manitowoc County in the east-central area states that adults are being found at the rate of 1 per sweep in individual fields there. Nymphs were noted for the first time on May 2 in Lafayette County, indicating that reproduction has begun. PEA APHID - Alfalfa fields sampled in the southern half of the state contained 2-6 per sweep. The average count for the period of May 4-9 was 3.5 per sweep, a modest increase from less than 1 per sweep the week before. MEADOW SPITTLEBUG - The first nymphs and spittle masses were observed in alfalfa late last week. Populations are currently below 2 per 100 stems in all fields checked in the south-central and central areas. PLANT BUGS - Representative counts range from 0.5-1 per sweep, which is still low relative to the economic threshold of 5 per sweep. Small nymphs of the tarnished and alfalfa plant bug species are appearing more commonly in sweep net collections. --Krista Hamilton, DATCP Entomologist 
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