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Corn
Volume 59 Number 14 Date 08/07/2014 WESTERN BEAN CUTWORM - The western bean cutworm degree day model indicates that 75% or more of the moth population has emerged as far north as Hancock in Waushara County. Trap counts have begun to decline across the southern half of the state. By contrast, emergence is about 50% complete in the north-central and northeastern counties where activity appears to have peaked in the past week. The high count for the period of July 31-August 6 was just 12 moths in the pheromone trap near Columbus in Columbia County. The cumulative state count to date is only 409 moths in 103 traps, the lowest total since surveys for this pest began in 2005. EUROPEAN CORN BORER - Moths of the second flight continue to appear in very low numbers in black light traps, signaling that eggs are being deposited on corn and other hosts. The peak of summer moth activity is expected to occur in southern and central Wisconsin by August 19. Sweet corn and non-Bt field corn should be inspected for egg masses and larvae before 2,100 degree days (modified base 50°F) are surpassed and the treatment window for second generation corn borers closes. Surveys this week found minor infestations affecting 4-12% of plants in Juneau, Monroe and Vernon counties. JAPANESE BEETLE - A DATCP survey specialist reports that approximately 2-3% of the plants in a Monroe County field had silks pruned to the ear tip and as many as three beetles per plant were feeding on the silks, potentially impairing pollination. Silk pruning was also noted in scattered fields in Juneau, La Crosse and Trempealeau counties. Control of this pest in field corn is warranted for populations that exceed three beetles per ear when pollination is incomplete. CORN ROOTWORM - Survey observations found counts of 0.1-1.3 beetles per plant this week, with above-threshold averages of 0.75 or more beetles in two fields in Monroe County. More beetles are appearing on silks as emergence accelerates. Crop advisors and corn growers should be aware that a study by Petzold-Maxwell et al., 2013 found that beetle emergence from Bt corn is delayed by an average of 12 days relative to non-Bt corn, suggesting that the scarcity of beetles as of early August does not necessarily indicate low populations for 2014. Beetle counts could increase sharply as emergence peaks this month. -- Krista Hamilton, DATCP Entomologist CORN EARWORM - Moth collections decreased during the week of July 31-August 6 from already very low levels. Only 16 moths were registered at 11 pheromone trap sites compared to 40 moths captured the previous week. Despite these low counts, the appearance of even a few moths in traps signals that sweet corn producers should continue to monitor fields with green silks. Counts this week were: Coon Valley 0, Cottage Grove 2, East Troy 0, Green Lake 3, Janesville 0, Madison 1, Marshfield 0, Mazomanie 0, Springvale 5, Sun Prairie 1 and Williamstown 4. -- Tracy Schilder, DATCP Plant Pest & Disease Specialist 
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