LAFAYETTE, INDIANA - Without question, the western bean cutworm receives the insect pest of the year award for field crops in 2010. This dubious honor is bestowed not so much for its economic damage, but rather its surge in numbers and spread in its short existence in Indiana. This pest's eastward migration from the western Corn Belt within the last decade has amazed and baffled many, certainly forcing us into a steep learning curve. We are indebted to many who have helped with moth trapping and/or field reports over the last five years, no doubt this has been a team effort.

Pheromone trapping for adults in 2010 began with a flurry. Our first catch was in LaPorte County on June 17, ten days earlier than previous years. In just a week's time, nearly 1500 moths had been captured and reports were coming in of egg masses being found in pre-tassel corn. Initially western bean cutworm activity was highest in areas of lighter soils and continuous corn in the northwestern counties. This likely is due to their success in overwintering, as larvae must burrow below the frost line to survive our winters. Within a couple weeks, moth numbers increased beyond these areas into crops on heavier soils, indicating that a significant amount of adult dispersal occurs. Being strong fliers certainly supports their ability to migrate to new counties/states potentially finding suitable food and overwintering habitats.

Peak moth flight occurred during the first week of July. Many reports of egg masses were being received at this time from northern counties. A very important finding was that high moth captures were an indication of their activity in an area, but often not predictive of infestations in adjoining fields. Pest managers quickly found that scouting all fields was necessary, especially those soon to tassel. Female moths are very discriminating about which plants are chosen for egg deposition. To complicate matters, fields with plants at different stages of growth (due to uneven emergence or excessive moisture) created clumped distributions of egg masses throughout fields. Those scouting for egg masses often found fields well below the 5% infested plants threshold, yet returned weeks later to find a high percentage of ear tips infested. When one considers that egg laying occurs over four or more weeks, with 20 or more larvae emerging, it becomes obvious that fields need to be scouted multiple times, ideally at intervals of less than a week.

Scouting programs for western bean cutworm were implemented by several agribusinesses in northwestern and north-central counties of the state. Not only did scouts monitor for adult flights with pheromone traps, but they usually followed up with frequent sampling for egg masses and larvae. Multiple fields were found to be at or above treatment threshold and were treated on a timely basis, being before larvae entered the ear. Foliar insecticides (primarily pyrethroids) did an excellent job of controlling western bean cutworm. These successful programs provide an alternative to utilizing Bt traited corn expressing the Cry1F protein (i.e., Herculex 1, Herculex XTRA, and SmartStax) or Agrisure's Viptera, all of which provide good but not 100% control - slight damage is often found on kernels of these traited hybrids.

Perhaps the biggest surprise of the season was the range of damage found in east central Indiana and west central Ohio. Conducted by Harvest Land Co-op, and coordinated by Steve Dlugosz, personnel from participating retailers sampled 198 client's fields for presence/absence of western bean cutworm larvae in ear tips. Of the 18 Ag Centers scattered throughout this region, 11 of them found larvae and ear tip damage. Although overall damage was minor, this effort certainly gave us a clearer understanding of the potential of this pest to expand beyond the northern counties. Whether or not this pest overwinters and establishes in these areas and builds to threatening levels will become clear next season and beyond.

SOURCE: Purdue University Extension