The largest corn I have seen has reached 5 leaves and soybeans at V1. Corn stands were not the only ones to suffer this spring. There have been soybean emergence issues in some fields planted before the heavy rain. Hypocotyls made it through before soil crusted, but cotyledons did not. I received photos where unifoliate and some trifoliate opened underground. Thanks, Corey. Others have reported similar. Weird, but bad enough in some fields for supplemental seeding.
Areas that received heavy rainfall in mid-May or areas north bear close watching for black cutworms. A history of early-season weeds such as lambsquarters or live cover crops increases the probability that moths found the field attractive for egg laying. A sharp-eyed consultant contacted me with a report and photo verification of black cutworms in sugarbeets in Pope and Kandiyohi Counties. Thanks, Darrel! We did not have a pheromone trap cooperator in those counties but neighboring counties to the south and west did pick up significant flights.
The consultant’s estimate of 2nd and 3rd instar larvae fits well with an early to mid-May moth arrival observed in pheromone traps. Another consultant cutworm reported infestations in Renville County sugarbeets. Occasionally, even a blind hog can find an acorn. Thanks, Steve! Scout high-risk fields in or near areas that received heavy rain in mid-May. In some of these, larvae are now large enough to cut corn. Thanks, Dave.
Remember, these reports do not mean every field is infested or is infested with economically threatening populations. Erratic stands from drown-outs and crusted soils can make stand evaluation and cutworm decisions difficult.
Higher plant populations and an ability to compensate for stand loss can reduce BCW risk to soybeans. Some fields in areas that were planted after large moth flights have poor soybean emergence due to crusting. Fields with marginal stands need to be scouted closely.
Remember, there are other species of cutworms that can attack Minnesota crops. Some of these are less injurious as they tend to cut plants above ground. The current and previous black cutworm reports, and a cutworm facts publication on scouting, ID, and thresholds can be found at https://swroc.cfans.umn.edu/research/ipm/bcw-network.
Don’t forget about armyworms in these areas either. I was finding small larvae in sweeps of SWROC oats yesterday. They were large enough to be seen – even with my old eyes. Next week, it might be worth a look at corn fields planted into rye cover, winter cereal crops, spring-planted cereals, or dense forage grasses on the edge of grass crops.
The recent warm rain helped trigger a grasshopper egg hatch. I found grasshopper nymphs at the UM SWROC today. These 1st instar (stage) nymphs are the first I have seen this year. These were probably red-legged grasshoppers, but I didn’t have a hand lens along for a proper ID.
Aster leafhopper numbers in oats increased this week. I suspect they came in with the system that brought rain on the 30th. Aster leafhopper’s potential to transmit the Aster yellows phytoplasma is a concern in susceptible crops such as garlic and carrots.
At the SWROC, adult alfalfa weevil populations appear to be slowly declining. 1st (predominate) to 3rd stage larvae are present. Cutting should provide good control if windrows are not left in the field for a prolonged period. Any survivors can be dealt with as needed in the second cutting. Hopefully, the weevil adult presence and hatch will be more orderly this spring. Small, variegated cutworm larvae were present in one of the fields I checked. Large larvae can cause severe damage under a windrow.
Corn borer moths should begin emerging next week in SW Minnesota.
At the SWROC we have accumulated 332-degree days (base 52) at the 4-inch soil depth. Eggs hatch of western corn rootworm starts around 380 DDs and peak hatch occurs at 684-767 DD. Remember, this, like most models, is not absolute. Based on both the projected rootworm development and corn stage, it is still too early to assess larval populations or root injury. If you want to time floating larvae or look for rootworm larvae, one alternative is to wait for fireflies to appear. I’ll do the degree-day calculations until peak hatch anyhow.
Happy trails,
Bruce