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Corn
Volume 64 Number 5 Date 05/30/2019 BLACK CUTWORM - Larvae resulting from the spring migration are now in the damaging late-instar stages in portions of southern and west-central Wisconsin. Signs of cutworm activity, such as small, irregular holes in the leaves and the presence of cut plants should be detectable in the 11% of corn emerged as of May 30. Many corn acres are at increased risk of attack this season as a result of significantly delayed planting and consistent moth flights throughout May. All corn should be closely monitored for cutworm feeding until the five-leaf stage. A threshold of 3% cutting of plants (with black cutworms still present in the field) has traditionally been used as the point at which growers should consider a rescue treatment. Early and timely detection of cutworm infestations is critical for controls to be effective. TRUE ARMYWORM - Substantial flights of 240 and 77 moths have been registered at the Janesville black light trap location in the last two weeks, indicating a potential for larval infestations in small grains and corn next month. Reduced tillage corn following sod or a small grains cover crop, and fields with early-season grassy weed pressure, are candidates for armyworm problems. Damage usually appears first in the perimeter rows of fields, where the larvae enter when moving from another food source. EUROPEAN CORN BORER - The degree day model for this insect suggests the first flight could begin shortly in advanced areas of the state where 374 heat units (modified base 50°F) have accumulated, including Beloit and Madison. Nightly temperatures have generally been too cold for moth flight, thus individuals are not yet appearing in black light trap collections. The spring flight is expected to start in the week ahead. CORN EARWORM - An early migration occurred during the reporting period ending May 29, as evidenced by the capture of 13 moths in the Janesville pheromone trap. In contrast to the black cutworm, corn is not at a critical growth stage where earworm damage can occur and these very early moths usually pose no threat to emerging fields. -- Krista Hamilton, DATCP Entomologist 
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