David Owens, Extension Entomologist; owensd@udel.edu
For the next 7 weeks, we will be maintaining true armyworm and black cutworm pheromone-baited universal moth bucket traps. Trapping data does not necessarily imply that a field is going to receive a damaging population of either pest. What traps can provide is a general indication of moth activity and, in the case of black cutworm, a good biofix for degree day calculations (see last week’s article on degree days here: http://extension.udel.edu/weeklycropupdate/?p=12842). BCW trap catches of about 2 moths per night trigger a degree day biofix, with a target of 300 DD, base 50 for larval scouting. Having said that, in several locations we have already exceeded this, so it is not possible to determine if our first significant BCW flight occurred this past week or a week earlier.
Complicating pheromone trap interpretation is the trap design itself. Some states use the wire cone traps you may see when we are surveying corn earworm (trapping for CEW will begin at the end of April). Kentucky has been trapping for TAW and BCW using cone traps for many years. In 2008, their traps peaked at 600 and 1700 TAW moths per week and wheat experienced worm outbreaks. Unfortunately, there is no clear pattern or correlation between the cone and bucket traps. That’s where your input is helpful, especially if you are growing organic or untraited corn that does not have as much worm protection. If you observe worm activity from either species, let us know. It is also important to keep in mind that both moths go to other grasses, not just small grains and corn and so may not necessarily be present in fields. It will help us learn more about these traps and what they mean.
| Trap Location | True Armyworm per night | Black Cutworm per night |
| Willards, MD | 1.1 | 2.6 |
| Salisbury, MD | 0.1 | 0.3 |
| Laurel, DE | 2 | 3.1 |
| Seaford, DE | 1.1 | 5.3 |
| Bridgeville, DE | 1.8 | 0.4 |
| Harrington, DE | 0.3 | 0 |
| Pearson’s Corner, DE | 0 | 0 |
| Kenton, DE | 2 | 0.1 |
| Smyrna, DE | 7.1 | 0.1 |
Wheat
Cereal leaf beetles are out there, somewhere. We found a single egg at the end of last week, and adult feeding scars in a couple of fields, but as of right now, this one appears to be a non-issue.
The previous week’s unusually warm weather has resulted in a large increase in aphid numbers. Bird cherry oat aphids have become abundant in several fields, whereas last week there were none. This aphid overwinters on wild cherry and migrates to small grain. Thresholds for small grains are about 150 per row foot and parasitoid/predator activity less than 1-2 per 100. Right now, predator activity seems to be delayed, but with the warm weather today, followed by somewhat cooler weather next week we may see predators and parasitoids catch up. If you hit threshold, what does that mean? It means that a spray may pay for itself. Will it pay more than that? With current prices, it might not. Predators and parasitoids might come in and control aphids. And with all the other field preparation and the planting season here, do you have the time?
Alfalfa
Scout your alfalfa now! First and second instars have been observed feeding in fields near Laurel. Count the number of larvae per stem from at least 30 stems in the field. Larvae can be dislodged by beating stems in a white bucket, or looking at stems through a magnifying lens. Thresholds depend on price of hay, number of weevils, height of alfalfa, and application cost. There is a good dynamic threshold for alfalfa weevil that can be found here: https://ento.psu.edu/extension/factsheets/alfalfa-weevil. Insecticide recommendations can be found here: https://cdn.extension.udel.edu/wp-content/uploads/2012/05/25073121/Insect-Control-in-Alfalfa-2018.pdf.