Agronomic Crop Insect Scouting

David Owens, Extension Entomologist; owensd@udel.edu

Soybean
Corn earworm moth flight has started a little earlier this year, and moth flight this year has generally been a bit higher than in recent years. Podworms have been sighted in the region beginning to infest soybean. Fields (or portions of fields) at risk for above threshold podworm infestation are open canopied, drought stressed, and flowering fields. As a reminder, podwoms generally have a greenish or dark striped color pattern. Head capsules are orange, and they have 4 pairs of abdominal prolegs. Unfortunately, this year much of our double crop soybean falls under this category. Fields should be scouted for weekly using a series of sweep samples. Thresholds can be calculated using NCSU’s threshold calculator: https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html. Using some ballpark estimates, a sweep threshold is going to be between 1.4 and 2.2 worms per 15 sweeps.

Sorghum
Flowering sorghum is extremely attractive to earworms (aka sorghum headworm) as well. Fields should be scouted for during the month of August, especially those that are heading out and those that are currently flowering. Heads that are at the end of or past the milk stage are much less likely to be infested. A good sampling method for sorghum is called the ‘beat bucket’ technique. About halfway down the webpage of the following link is a good description and video of the beat bucket: https://betteryield.agrilife.org/category/sorghum/. Basically, you beat the sorghum head into a bucket to dislodge worms. In general, 1 earworm per head is associated with a 5% yield loss. You can use that to work through the appropriate decision calculations: Control cost – estimated yield loss potential x estimated yield x value of sorghum. Note, both fall armyworm and corn earworm will feed on the heads and are about equally damaging. Also note that thresholds assume the insecticide has greater than 80-90% efficacy. There is potential that we do not realize that level of control with a pyrethroid. If using an insecticide, use a higher volume and high pressure to drive material into the head as much as possible.

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