Warmer Temperatures & Tail Winds Of Helene Might Cause An Outbreak Of Fall Armyworm In Cover Crops In Central KY
DR. RAUL T. VILLANUEVA
LEXINGTON, KENTUCKY
Current Situation. During the previous 2 weeks there have been two articles (Testing Low-Tech Trap to Detect Egg Masses of Fall Armyworm in Corn & Forage Fieldsand,Not Only the Fall Armyworm is Present in Fields of Kentucky, but Other Spodoptera Species During the 2024-Fall) related to the fall armyworm (FAW) (Spodoptera frugiperda) in the KPN blog. You can find some information on its biology, identification, and phenology in these articles. You will also find data about numbers of eggs and adults collected in black polypropylene fabric traps to detect FAW egg masses and pheromone-based traps to detect male adult fall armyworm in August and September 2024.
Phillip Anderson, a crop consultant from Daviess County, reported a significant outbreak of fall armyworms (FAW, Spodoptera frugiperda, Noctuidae) in cover crop wheat and rye. FAW were also identified in pastures located in reclaimed land from coal mines. Mr. Anderson reported that at least six different fields had this FAW outbreak, corresponding to approximately 500 acres of wheat and rye cover crops (Figure 1). Injury to seedlings (Figure 2) and Feekes 1, 2, and 3 (Figure 3) have been observed recently. This finding happened on October 8, 2024. In addition, in Princeton no FAW egg masses were found on September 27. However, pheromone-based bucket traps captured 10, 1, and 5 FAW adults in corn and 50, 189, and 29 FAW adults in alfalfa on September 27 and October 4, and 11, respectively. These FAW captures in late September and early October may be due to the warmer temperatures being recorded, and/or the FAW adults might have been carried by the tail winds of Hurricane Helene.
Based on the results from the egg traps and the pheromone-based traps shown and described in the articles mentioned above, it seems that the fall armyworm strain abundant in Kentucky this year might be the rice strain, which has preference for rice, wheat, rye, and pastures. Also, the pheromone-based traps showed an increase in the male adult moths flying or migrating northward.
Management & Discussion
finding was confirmed by Dr. Batista, who visited this field that day. Dr. Batista collected 82 live caterpillars after the field was sprayed and took them to the entomology laboratory at the UK Research & Education Center at Princeton. Only 12 of the 82 caterpillars died 1 day after the spray, and 1 more died 3 days after the spray on October 11. These are mortalities of 14.6% and 15.8% for 1 and 3 days after the spray, respectively. Since most FAW caterpillars found in this field were between 2nd and 3rd instar, these observations indicated that the October-2024 outbreak may be of FAW populations resistant to beta-cyfluthrin. However, this farmer was using this insecticide to control stinkbugs on soybeans previously this year, and this may have contributed to the low mortality. Also, the tail winds from Hurricane Helene might have brought a population of FAW resistant to beta-cyfluthrin from the south.
In addition, if farmers are observing low mortalities using pyrethroids to control 1st to 3rd instar FAW in their fields, Steward® (indoxacarb, group 22A) and Besiege® (λ-cyhalothrin + chlorantraniliprole, groups 3A and 28) insecticides can be used, but these insecticides are more expensive. It is worth noticing that the seeds used for wheat and rye in these fields were not treated with insecticides. Early detection of FAW infestations will allow for more effective control of FAW if larvae are in the 1st to 3rd instars or smaller than 1/2 inch in length. The insecticide efficacy decreases significantly when caterpillars are from 4th to 6th instar. If sprays are necessary, consult with your county Extension agent. ∆
DR. RAUL T. VILLANUEVA: University of Kentucky