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Corn
Volume 62 Number 14 Date 08/03/2017


WESTERN BEAN CUTWORM - Moth counts escalated significantly this week at monitoring sites in Columbia, Dodge, Green Lake and Marquette counties. Pheromone traps captured 747 moths from July 27-August 2, compared to 477 moths the week before. Counts across southern and central Wisconsin have likely peaked and should begin to decline soon. Moth emergence is expected to continue in the northern areas for two more weeks. Preliminary results of the 13th annual trapping survey show that the 2017 state count of 1,677 moths in 70 pheromone traps (24 per trap average) is now larger than the 2016 cumulative capture of 1,530 moths in 75 pheromone traps (20 per trap average). The highest individual trap total as of August 2 is 211 moths registered near Cambria in Columbia County.

EUROPEAN CORN BORER - The peak in summer moth activity should occur before August 12 in the southern and central counties and around August 21 in the northern counties. Pupae and fifth-instar larvae are still common in many cornfields, and these stages will contribute to the flight in coming weeks. The treatment period for second generation larvae has opened across the southern two-thirds of the state with the accumulation of 1,550 degree days (modified base 50F).

JAPANESE BEETLE - A DATCP survey specialist reports that approximately 60% of the plants in a La Crosse County field had silks pruned to the ear tip and as many as 12 beetles per plant were feeding on the silks, potentially impairing pollination. A similar infestation involving 50% of the border plants and 5-6 beetles per ear was noted in Dane County. Silk pruning has become evident along field edges, although at most sites the heaviest feeding is limited to the outer rows and the infestations do not extend into the field interior. Control of this pest in corn is warranted if field-wide populations exceed three beetles per ear and pollination is less than 50% complete. Chemical treatment of entire fields is seldom necessary. Border area spot treatments are usually sufficient for reducing beetles during the critical pollination period.

CORN ROOTWORM - Corn surveyed in the southern and central districts yielded variable averages of 0-2.9 beetles per plant, with the week's highest population recorded near Lancaster in Grant County. Economic averages of 0.75 or more beetles per plant were found in only 7 of 78 fields sampled from July 31-August 2. Counts at most sites are still fairly low for early August. The 2017 beetle survey is now in progress and will continue for the next 2-3 weeks.

CORN EARWORM - Counts remained low during the past week. Thirty-eight moths were registered at 15 pheromone trap sites, compared to 24 moths captured the previous week. Despite the low numbers, the arrival of even a few moths in traps signals that sweet corn producers should begin monitoring fields with green silks. Small larvae were observed this week in corn ears in a field near Tomah in Monroe County.

-- Krista Hamilton, DATCP Entomologist