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Forages & Grains
Volume 64 Number 11 Date 07/11/2019 POTATO LEAFHOPPER - Counts in alfalfa have increased above established economic thresholds in many fields. Levels at some sites are extremely high. Surveys conducted in Grant, Lafayette, Richland and Vernon counties found a range of 0.9-7.0 adults and nymphs per sweep and a very high average of 3.5 per sweep. Two Grant County fields, one near Fennimore and the other near Benton, had averages of 7.0 per sweep. Counts in Adams, Juneau, Marquette, Green Lake and Waushara counties were also generally high and varied from 0.1-4.3 per sweep, with an average of 1.7 per sweep. Of the 40 fields sampled this week, 19 or 48% had economic leafhopper populations. Adjusting harvest schedules cannot generally be used to manage leafhopper population buildup. Control may be necessary when scouting indicates populations have exceeded the economic threshold of 1.0 per sweep for alfalfa 8-11 inches and 2.0 per sweep for fields 12 inches or taller. PEA APHID - Populations have decreased sharply since late June. The average from July 4-10 was only 0.5 per sweep. Potato leafhoppers have replaced pea aphids as the most abundant insect pest in alfalfa at this time. ALFALFA WEEVIL - Pupation is occurring statewide and feeding should subside next week. Larval populations in central and southwestern Wisconsin have declined to near zero in the past two weeks, with 0-10 weevils per 100 sweeps being the typical count. PLANT BUG - Combined averages of the alfalfa and tarnished plant bugs varied from 0-0.2 per sweep and averaged 0.1 per sweep. These counts are considered extremely low for this pest. Once again, the economic threshold for combined counts of plant bug adults and nymphs is 5.0 per sweep. -- Krista Hamilton, DATCP Entomologist 
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