Participants in the University of Minnesota Cooperative Black Cutworm Reporting Network have noted more migrating moths, particularly in the western part of Minnesota, according to Bruce Potter, a U-M Extension IPM specialist based in Lamberton.

Since early April, participants have been checking pheromone traps for black cutworm moths headed north from the southern U.S.

In a weekly blog, Potter says two traps in western Minnesota in early May had significant captures. A Lac Qui Parle County trap captured nine moths from May 5-6 and a Murray County trap captured 12 moths over the same period. Traps in other counties also captured moths throughout the week.

“Fortunately, when and where these larger flights arrived in Minnesota, most corn and sugar beet, and many soybean fields, had been already been worked and planted, thereby reducing their attractiveness to moths laying eggs,” he says.

Risk of economic damage

While the timing of 2020 black cutworm moth arrival into Minnesota is similar to 2019, Potter says the frequency, distribution and magnitude of the flights have been much less. When these data on this year’s fewer and smaller flights are combined with the early planting in the southern portion of Minnesota, the risk of economic damage appears low compared to many years. This risk, however, is not zero.

Black cutworm moths arriving in Minnesota seek out areas with crop debris, sheltered areas and low-lying spots in the field to lay eggs. Any early season weed growth is very attractive to the moths.

Areas with dense populations of winter annual (e.g. shepherds’ purse) and early spring emerging broadleaf weeds (e.g. lambsquarters) are often infested. Similarly, overwintering cover crops might attract egg-laying moths and black cutworm damage associated with winter rye has been observed in Minnesota corn, Potter says.

Unworked fields or fields with reduced tillage and more crop debris is on the surface attract more egg laying moths. Fall tillage that buries crop residue and spring tillage that eliminates early spring weed growth before the flight arrives reduces the risk and severity of black cutworm attack.

Historically, soybean residue is more attractive than corn, but this may be in part due to the amount of fall tillage or to species and numbers of broadleaf weeds in the seedbank between the two crops, he added.

Focus scouting efforts

How do you focus your scouting efforts for black cutworm? Fields that are at highest risk are fields that had not been worked when moths arrive, fields with winter annuals or early spring emerging weeds and in the case of corn, field planted to hybrids without a Cry1F (HX1) or Vip 3a (Viptera) above-ground Bt traits.

In the case of corn, scouting for black cutworms should start before 300 degree-days (base 50 F) accumulate after a significant moth capture (eight or more moths per two nights) occurs.

“This is about three weeks in a typical Minnesota spring but will, of course, happen sooner if warm and later if cool,” Potter says. “Eggs hatch and leaf feeding begin at 90 degree-days so early scouting of small broadleaf seedlings, such as sugar beets, is important.”

For a couple of the smaller, early black cutworm immigration events and early May’s significant captures, predicted dates for the start of leaf-feeding and for the beginning and end of cutting are shown in Table 1.

PREDICTED IMPACT: U-M Extension has projected dates of leaf feeding and for the beginning and end of cutting for black cutworms. Projections are based on dates that moths were captured in surveillance traps in late April and early May.

“Although we did not have any significant flights until May 5-6, there may already be some leaf-feeding from larvae resulting from earlier migrants,” Potter says. “These larvae might be large enough to cut corn as early as May 24th. Since both [black cutworm] and frost injury prefer low–lying areas, the recent four- to five-night freeze event could make scouting more difficult in some parts of Minnesota.”

For more information on black cutworm, read the May 14th and earlier reports of the 2020 University of Minnesota Cooperative Black Cutworm Trapping Network online. You can also learn more about cutworm ID and economic thresholds.

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