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Preparing for western bean cutworm in 2017

#PestPatrol with Tracey Baute, OMAFRA

Western bean cutworm (WBC) has earned the designation of primary pest of corn in Ontario, and it is starting to become important for dry bean growers too. Quality concerns outweigh yield loss with this pest, and when conditions are conducive to mycotoxins, as in 2016, WBC’s impact is very evident.

The flurry of tweets under #spray2017 indicates that this coming year is going to be a busy one for western bean cutworm management.

How to prepare for 2017

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  • Trapping is important. It tells you if and when moths are active in your area. Thresholds are not based on trap counts (since traps only catch the males while the females are still free to lay their eggs) but they do tell you when to start scouting.
  • Join the Ontario WBC Trap Network at Data entered on our site is displayed that same week on interactive maps so we can see where moths are active and when scouting is required.
  • Crop stage plays a huge role. If a field has a variable plant stand, or fields in the area vary in crop stage, the female moths will continue to find ideal plants to lay their eggs on. Female moths prefer to lay their eggs on late-whorl to very early tasseling corn plants. Too early, when there is no tassel developing, will result in the larvae starving to death.
  • Scouting should begin as soon as the corn in the area is close to the late-whorl stage (when you can feel a tassel developing inside the whorl).
  • Plan to scout every four to six days, over a three- to four-week period during late-whorl until early-silk stage. Inspect the top three to four leaves on 20 plants in five areas of the field. Pay attention to those areas of the field that are delayed in crop stage compared with the rest of the field. Females will be attracted to those younger plants. Document the percentage of plants infested with egg masses or small larvae.
  • The action threshold in the Great Lakes Region is lower than in the western U.S. Spray is warranted if there has been an accumulation of five per cent of the plants with eggs or small larvae. So, if during Scouting Trip 1, there were two per cent of the plants with eggs on them, and four days later during Scouting Trip 2 there are three per cent, then there is a need to spray.
  • Timing of application must coincide with egg hatch when young larvae are feeding at the tops of the plants, prior to their entering the ears.
  • Scout all corn hybrids, including those containing Bt. Hybrids containing Cry1F no longer provide protection against WBC and even those hybrids containing Viptera technology should be scouted to confirm that the Bt trait is still effective.
  • WBC is much more difficult to scout for in dry beans. If WBC has reached a threshold in the neighbouring corn field, adjacent dry bean fields are likely at risk, especially if the corn fields have passed the early tassel stage and moths are still actively flying, as indicated by the pheromone traps. If entry holes are observed in the pods, an insecticide application is necessary.

Newly hatched western bean cutworm (first instars).
photo: Supplied

Tracey Baute is a Field Crop Entomologist with OMAFRA. Follow her on Twitter @TraceyBaute.

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