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Corn
Volume 61 Number 13 Date 07/28/2016 JAPANESE BEETLE - Moderate infestations of 10-30 beetles per 100 plants have been observed since early July in scattered fields in the southern and west-central counties. The greatest threat to corn at this time of year is when large numbers of beetles converge on corn silks, potentially impairing pollination. Control is warranted for populations that exceed three beetles per ear when pollination is occurring. WESTERN BEAN CUTWORM - The western bean cutworm degree day model indicates that 75% or more of the moth population has emerged near Beloit, La Crosse, Spring Green and other advanced locations. Emergence is about 50% complete in the central counties where activity appears to have peaked. High counts for the period of July 21-27 was 71 moths in the pheromone trap near Markesan in Marquette County and 32 in the Beaver Dam (Dodge County) black light trap. The cumulative state count to date is 1,185 moths in 75 pheromone traps, which is still comparatively low based on the trap counts documented since surveys for this pest began in Wisconsin in 2005. EUROPEAN CORN BORER - Moths of the second flight continue to appear in black light traps, signaling that eggs are being deposited on corn and other hosts. The peak of summer moth activity can be expected by August 12 across the southern two-thirds of Wisconsin. 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. CORN LEAF APHID - Light populations of 15-40 aphids per plant were noted on a few corn plants in La Crosse and Monroe County fields on July 25. Pressure of 50 or more aphids per plant on 50% of the tassels and silks can interfere with pollination and may require treatment. CORN EARWORM - Moth counts remained low this week, with pheromone traps in Cottage Grove, Madison, Mayville, Pardeeville, and Ripon registering only 1-5 migrants per trap. A pheromone trap capture of 5-10 moths for three consecutive nights indicates the need for protective treatment of sweet corn fields with green silks. Counts for the week ending July 27 were as follows: Arlington 0, Beaver Dam 0, , Coon Valley 0, Cottage Grove 1, Hancock 0, Janesville 0, Madison 1, , Marshfield 0, Mayville 5, Pardeeville 3, Prairie du Chien 0, Ripon 1, Sun Prairie 0, Sun Prairie North 0, Watertown 0, Waupun 0 and Wausau 0. -- Krista Hamilton, DATCP Entomologist 
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