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Forages & Grains
Volume 58 Number 12 Date 07/24/2014 POTATO LEAFHOPPER - Nymph production has intensified. Alfalfa fields surveyed in the southwest, south-central and central counties now contain averages of 0.1-1.3 adult and nymph leafhoppers per sweep, as compared to 0.1-0.9 per sweep last week. Reports from northwestern Wisconsin indicate populations there have exceeded the two-leafhopper-per-plant (for 12-inch and taller alfalfa) economic threshold in a few fields, although DATCP surveys have found no economic counts as of July 23. The hot, dry weather this week has favored the increase, and higher populations may develop in the third crop if similar conditions prevail in early August. PLANT BUG - Counts of this insect vary considerably from field to field, but the average remains very low at 0.3 per sweep. Nymphs in all developmental stages were found in third crop alfalfa sampled this week and these immature plant bugs constitute 25-50% of the population in most fields. PEA APHID - A typical net sweep in alfalfa in the southern half of the state currently yields only 0.1-0.3 aphids, a pronounced decline from average counts of 5-6 per sweep at the end of June. Limited pea aphid activity has been observed since populations collapsed three weeks ago. TRUE ARMYWORM - Alfalfa surveyed in the southern and central counties showed low counts of small (¼-½ inch) second generation larvae. Numbers ranged from 1-3 per 10 sweeps. The principal threat from armyworms in alfalfa is when the larvae migrate to other crops as fields are harvested. -- Krista Hamilton, DATCP Entomologist 
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