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Forages & Grains

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Degree Days

Corn
Volume 52 Number 8 Date 06/15/2017


EUROPEAN CORN BORER - The treatment window for first-generation larvae has opened near Janesville, La Crosse, Spring Green and other advanced southern and western locations. Close inspection of conventional cornfields and sweet corn for eggs, small larvae, and early whorl feeding is particularly important during the next two weeks. Controls directed against the early-instar stages must be applied before the caterpillars begin boring into corn stalks and midribs. At average June temperatures, the 300 degree day corn borer treatment window from 800-1,100 GDDs (modified base 50F) is equivalent to about 15 calendar days. Larvae are susceptible to chemical control for only about a week after egg hatch.

STALK BORER - Light feeding injury was noted in La Crosse, Monroe, Trempealeau and Vernon counties where 1-11% of corn plants in the edge rows were damaged. This mid-season pest migrates from perennial grasses and broadleaf weed hosts in early June and infests predominantly the first 4-6 rows of corn. Leaf feeding is expected to become pronounced by the end of the month and spot treatment may be justified for severe infestations. Scouting is recommended through the V7 stage since Bt corn hybrids suppress but will not completely control stalk borers.

WESTERN BEAN CUTWORM - Pheromone traps are now being set in preparation for the annual moth flight. Participants in the western bean cutworm monitoring program are reminded to begin reporting counts to Tracy Schilder at tracy.schilder@wisconsin.gov by June 21 and each Wednesday during the 10-week trapping survey.

BLACK CUTWORM - The threat from this early-season pest has not subsided, and isolated problems could develop in later planted corn. Scouting may be discontinued once plants reach the V5 stage.

CORN ROOTWORM - Peak egg hatch is predicted to occur between 684 and 767 degree days (modified base 52F), or by June 18 from La Crosse south to Janesville, by June 24 in the southeast and central areas, and by June 27 near Wausau. The first adult rootworm beetles usually appear around Independence Day.

-- Krista Hamilton, DATCP Entomologist