This fall, we may see an outbreak of armyworms and/or grasshoppers. If you have lush green winter pasture or any pasture, for that matter it may be a prime target.
The first step to combating these pests is to properly scout for them. I usually recommend scouting every two to three days, but, this year, it may be worth looking every day for the first two to three weeks after small grain emergence. For both pests, I prefer to scout first thing in the morning when the insects are moving more slowly from the cooler temperatures. This also gives me the rest of the day to get the field sprayed, if needed.
For grasshoppers, start by looking around field edges, fences, ditches and weedy areas. Count the number of grasshoppers you see in a one-square-foot area. Move about 50 feet and count again. Do this 18 times and divide by two to get the number of grasshoppers per square yard. Typically, the treatment threshold is three per square yard in wheat and seven to 10 per square yard in the vegetation next to a wheat field. However, this is calculated based on the average value of the wheat. This year, the fall wheat forage is probably worth much more considering the shortage of forage and hay in many areas. Therefore, the treatment threshold may be lower.
Some general-use chemicals for grasshopper control in wheat are dimethoate, malathion and carbaryl. Restricted-use pesticides include, but are not limited to, lambda-cyhalothrin, chlorpyrifos, zeta-cypermethrin, methyl parathion and gamma-cyhalothrin. Best control will occur when grasshoppers are small, before they have wings.
For fall armyworms, start by watching for moth flights. You know when this occurs by the severity of gray moths that cover your windshield when driving at night. This is the time when the moths are laying eggs. Two to 10 days later, the eggs hatch and larvae begin feeding in hoards. Young larvae are slightly greenish and have black heads. Mature larvae vary from greenish to grayish brown, have stripes running lengthwise down their sides and have a light tan or yellow inverted "Y" on their brown heads. Count the number of larvae found in a square foot or per foot of row. Do this in 10 places around the field and average the number. Typically, the treatment threshold is three to four larvae per foot of row or square foot with feeding damage evident. Again, that threshold may need to be lower this year.
Some general-use chemicals for fall armyworm control in wheat are carbaryl and spinosad. Restricted-use pesticides include, but are not limited to, lambda-cyhalothrin, methomyl, methyl parathion, zeta-cypermethrin and gamma-cyhalothrin.
There are also other armyworms, including beet armyworms. Scouting will be similar, but the chemical selection is narrower. For beet armyworms, try zeta-cypermethrin.
Whatever chemical you use, be sure to read and follow all label directions, including grazing restrictions. For more information, call the Noble Research Institute at (580) 224-6500.
