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Corn
Volume 63 Number 15 Date 08/16/2018


CORN ROOTWORM - The late-summer beetle survey is now in progress. Results from July 31-August 16 indicate populations are generally low across southern and central Wisconsin. Above-threshold averages of 0.75 or more beetles per plant were found in only 6 of 81 fields (7%), while beetles were not found in a large percentage of the sampled fields (67%). The current survey average is very low at 0.2 per plant. More rootworm adults are expected to appear on silks in later-planted fields as beetle emergence continues, therefore scouting to determine this season's corn rootworm pressure and to forecast the risk of larval root injury to continuous corn in 2019 should be conducted in the next 2-3 weeks.

WESTERN BEAN CUTWORM - Moth counts have declined at most monitoring locations. The traps in Marinette and Oconto counties continued to register very low captures of 3-6 moths per trap this week, while counts at nearly all other sites fell to near zero for the reporting period. As of August 16, the state cumulative total is 619 moths in 55 traps (11 per trap average), a marked decrease from the 1,856 moths in 70 traps (27 per trap average) collected last season. The highest individual count for the nine-week monitoring period is 78 moths near Durand in Pepin County.

EUROPEAN CORN BORER - The treatment window for second-generation larvae has closed near Beloit, Eau Claire, La Crosse, Lancaster and Madison, but will remain open for 1-2 more weeks in parts of central and northern Wisconsin. Final inspections should be performed before degree day accumulations surpass 2,100 (modified base 50F) and larvae begin boring into corn stalks. Due to the variability in corn borer development across the state, sweet corn growers are advised to evaluate fields carefully and base control decisions on the specific conditions observed.

JAPANESE BEETLE - This insect is still common in cornfield perimeters across much of the state. Beetles were noted feeding on corn silks this week from Grant to Wood County, with most infestations limited to the outer 10-12 rows of the field. As a reminder, a field-wide average of three or more beetles per ear is considered high and may be a concern for fields not yet pollinated.

CORN EARWORM - The first significant migrations into Wisconsin of the 2018 season were registered this week. Locally moderate to heavy flights of 53-206 moths per trap were reported from the Arlington, Beaver Dam, Cottage Grove, Mayville, and Sun Prairie monitoring locations. A cumulative total of 850 moths have been captured in 15 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 16 were: Arlington 57, Beaver Dam 53, Coon Valley 15, Cottage Grove 63, Hancock 4, Janesville 28, Madison North 45, Marshfield 0, Mayville 206, Pardeeville 26, Prairie du Chien 0, Ripon 16, Sun Prairie 94, Watertown 15, and Wausau 0.

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 appear early and populations grow rapidly, and a large percentage of corn tassels become saturated with aphids and their honeydew secretions.

-- Krista Hamilton, DATCP Entomologist