IPM Crop Survey - Insect Update (07/08/21)
Cereal aphids were observed in 23% of the wheat fields scouted last week including SE (Ransom, Richland, LaMoure, Sargent counties); EC (Barnes, Cass counties); Central (Eddy, Stutsman, Wells counties) and NE (Grand Forks county). The percent of plants infested ranged from 1-100%. Hot spots were in Barnes and Cass counties; however, these fields were maturing wheat, Zadoks 80-82 (dough development). Growth stages of wheat are varying widely from only Zadoks 21 (main shoot and one tiller) to mature 83 (early dough). Cereal crops are quickly maturing due to extreme heat and drought, and aphids will be moving to other crops like corn. Only late-planted wheat in the heading stages (prior to Zadoks 59) are still susceptible to yield loss when >85% of the plants are infested with one or more aphids. See last week’s Crop & Pest Report #10, July 1st for more information.
Grasshoppers also are maturing quickly with the heat last week and some nymphs are already late instar nymphs, which will be molting into adult grasshoppers, probably in the next one-two weeks. We are at least two weeks ahead in grasshopper development. About 80% of the fields scouted had grasshoppers present at field margins and the density of grasshoppers ranged from 1-16 nymphs per square yard. There has been reports of edge spraying by growers in hot spots. Needless to say, continue to scout for increasing and yield-robbing grasshopper infestations frequently this year. Economic threshold for nymphs is 30-45 nymphs per square yard in field and 50-75 nymphs per square yard in field margins. If you are having trouble counting that many, use a 15-inch sweep net and four 180-degree sweeps equals one square yard. Or, convert to the number per square foot - 3-5 nymphs per square yard in field and 6-8 nymphs per square foot in field margins.
Soybean aphids were observed in 9% of the soybean fields scouted last week and found only in Cass and Grand Forks counties of ND. The percent of plants infested was 3-19% and the average number of aphids per plant was 1-32 in infested fields. Growth stages of soybeans ranged widely from only V4 to R2 (full bloom). Continue to scout soybean fields at least weekly through R6 (full seed).
Spider mites are hard to find and were observed in only 2 fields located in Grand Forks and Pembina counties. The forecast for rains and cooler temperatures will help mitigate any increases in populations for at least the next week.
IPM maps of insect pests and diseases are posted on the IPM website: https://www.ag.ndsu.edu/ndipm