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Planting later sets stage for possible Black Cutworm injury

Spring storms prior to tillage and planting provided favorable conditions for this pest Corn plants are most vulnerable up to the V4 stage and susceptible up to the V6 stage The following practices are recommended for management monitor flight reports scout fields and incorporate tillage Consider a rescue treatment if plants are small cutworms are active and economic thresholds are exceeded Broadcast pesticide or bait application may be used as a rescue treatmentPhoto WM Hantsbarger Bugwood
An early warning sign of potential economic damage includes small pinhole feeding injury in leaves.

While planting has been slow in 2022, moth flights have been steady across much of the state. Regular flights have been observed through much of the northern two-thirds of the state. Several counties have reported significant moth flights (9 or more moths over a 2-night span). We can use the date of the significant flight to predict potential cutting dates based on degree day predictions.

University of Illinois5-20-21 BCW-cutting-projections.jpg

Projected cutting dates based on moth trap captures and degree day accumulations. *Please not these are just projections, feeding and cutting could occur earlier than anticipated.

A few key things to note:

Black cutworm moths are strong migratory insects with northward flights commonly observed from Gulf States into the Midwest from March through May. Moths are attracted to fields heavily infested with weeds such as chickweed, shepherd’s purse, peppergrass, and yellow rocket. Late tillage and planting tends to increase the susceptibility of fields to black cutworm infestations.

Cutting of corn plants begins when larvae reach the 4th instar — with a single cutworm cutting an average of 3 to 4 plants during its larval development. Cutting tends to occur most often during nights or on dark overcast days. Fields at greatest risk to cutting and economic damage are in the 1-to-4 leaf stage of plant development.

An early warning sign of potential economic damage includes small pinhole feeding injury in leaves (caused by the first 3 instars). Producers are encouraged to look for early signs of leaf feeding as a potential indicator of cutting, rather than waiting for cutting to take place. With prolonged flights and later planted corn, feeding may continue into the early weeks of June.

Don’t assume that all Bt hybrids offer the same level of cutworm protection. Not all Bt hybrids offer adequate protection against black cutworm damage. Growers should consult the Handy Bt trait table prepared by Dr. Chris DiFonzo at Michigan State University to determine the level of protection provided by their chosen Bt hybrid. Plants in the 1- to 4-leaf stage are most susceptible to cutting. Cutting of plants earlier than these projected cutting dates is possible — localized intense flights may have occurred and were not picked up by our volunteers.

A nominal threshold of 3% cutting of plants has traditionally been used as a point at which growers should consider a rescue treatment.

Source: University of Illinois, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset. 

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