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Corn
Volume 65 Number 15 Date 08/13/2020 CORN ROOTWORM - DATCP's annual beetle survey is now in progress. Preliminary results from July 30-August 13 indicate populations have increased in all three western districts (northwest, west-central and southwest). Above-threshold averages of 0.75 or more beetles per plant have been found in 36 of the 121 fields (30%) sampled to date, with the heaviest pressure recorded in southwestern fields. Corn producers should be aware of the potential for corn rootworm adults to redistribute from earlier silking fields to later-planted fields as beetle emergence peaks. Now is the time to scout to determine this season's beetle pressure and to forecast the risk of larval root injury to continuous corn in 2021. CORN LEAF APHID - Colonies of this aphid are appearing on corn ears and leaves in southern and western Wisconsin. Corn leaf aphids usually do not interfere with pollination unless they develop early and populations grow rapidly, and a large percentage of corn tassels become saturated with aphids and their honeydew secretions. WESTERN BEAN CUTWORM - Moth counts have declined at most monitoring locations. Three traps in Clark and Green Lake counties continued to register moderate captures of 25-55 moths per trap this week, while counts at nearly all other sites fell below 10 moths for the reporting period. As of August 13, the state cumulative total is 3,748 moths in 58 traps (64 per trap average). The highest individual count for the 10-week monitoring period is 382 moths near Princeton in Green Lake County. EUROPEAN CORN BORER - The treatment window for second-generation larvae has closed near Beloit, Lancaster, and Platteville, but will remain open for one more week in parts of southern and central Wisconsin. Final inspections should be performed before degree day accumulations surpass 2,100 (modified base 50°F) and larvae begin boring into corn stalks. CORN EARWORM - Locally significant flights of 25-51 moths per trap were reported from the Arlington, Bristol, Mayville, and Ripon monitoring locations, while the 14 other sites collected no more than 10 moths per trap during the week. A cumulative total of 784 moths have been captured in 18 pheromone traps to date. Sweet corn growers should continue to follow CEW migration reports and maintain treatments as long as moth activity persists and green silks are available for oviposition. Counts for the week ending August 12 were: Arlington 3, Arlington North 27, Bristol 33, Coon Valley 10, Cottage Grove 4, Madison North (airport) 2, Manitowoc 3, Mayville 25, Ripon 51, Sun Prairie 5, Sun Prairie North 1 and Watertown 2. -- Krista Hamilton, DATCP Entomologist 
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