Stink Bugs Could Still be a Problem in Soybeans

Doug Johnson, Extension Entomologist

Because of delayed planting and a cool summer, Kentucky soybean producers are likely to have considerable acreage of late maturing soybeans. This probably causes most folks to be concerned with frost. However,this extended maturity may also set up fields for additional damage by stink bugs. Producers and consultants should remain watchful as long as pods are still filling.

Capture of corn earworm moths in IPM pheromone baited traps at UK-REC, Princeton (Caldwell Co.) Ky in 2012.

Doug Johnson, Extension Entomologist

CEW caterpillar and damge on soybean.

Corn ear worm (CEW), also known as soybean podworm, are currently active in soybeans. This is a direct damage pest as it feeds on pods, seeds, & petioles. You are unlikely to detect this pest by checking for defoliation because it does not feed much on leaves. There is no sure way to detect this pest in your soybean crop except to scout for it. This means sweeping or direct visual examination of the pods.

CEW may occur in many color phases. It sometimes appears very dark, almost black, to brown to red and green. The green color phase is most often seen when feeding in soybeans. When fully grown, the larvae are about 1 ½“ long. They are marked by alternating light and dark stripes running the entire length of the body. These stripes are not always the same from one caterpillar to another. Usually a double dark stripe will run down the middle of the back.

You can certainly look for direct damage feeding on the pods to see if they are causing damage. In rows narrower than 30”, sweeping with a 15” sweep net is about the only way to measure this pest. The threshold is 9 worms per 25 sweeps.

Capture of CEW moths at UKREC 2012

We do know that corn earworm moth flight has been increasing and populations are greater than we normally see. Moth capture in our IPM pheromone baited traps at the UK-REC in Princeton is shown in Figure 2. Remember, these are moth counts and moths are NOT the damaging stage. Caterpillars will appear about a week after the moth flight. In 2012, moth numbers (green line) are greater than the rolling five- year average (blue line) so we are at an elevated risk of damage from this pest compared to most years. However, trap captures will NOT tell you what will happen in an individual field. Only field sampling will help you establish whether or not a threshold has been met. Moth flight numbers will give you a week or two heads up on what might happen.

If insecticide control is warranted, you may find products listed for control of CEW in soybeans online at: http://pest.ca.uky.edu/EXT/Recs/welcomerecs.html or from your County Extension Office. Be wary of spraying too early, you may kill the predatory insects that are providing some natural control and miss the actual pest.

Green Cloverworms Appearing in Large Numbers in Soybeans.

Doug Johnson, Extension Entomologist

There are some unusually large populations of green cloverworms on soybeans scattered around the state. This is a very common insect in soybeans which always has the potential for economic damage, but very rarely causes economic damage. The populations I have seen thus far are not at the economic threshold, but were much larger than I am used to seeing. It makes sense to look at your soybeans, especially late planted or slow developing beans.

Green cloverworm caterpillar on soybean stem.

Green cloverworm is easy to find and easy to identify. These worms are light green with two thin white stripes along each side of the body. When fully grown, these slender worms are 1” to 1-1/2“ long. They have only three pair of prologs in the center of their body. Most of the other caterpillars in KY grown soybeans have either 4 or 2 pair of prolegs. Green cloverworm will become very active, wiggling and looping when disturbed.

These pests are foliage feeders. They will strip the leaf tissue from between the veins leaving the veins, petioles and stems behind like a skeleton.

It takes a great many of these caterpillars to cause an economic problem. Economic threshold (ET) depends not only upon the number of green cloverworms, but also on the stage of the plants, the value of the beans, and the cost of treatments. ETs may be found in:

IPM-3, KY IPM Manual for Soybeans at: http://www.uky.edu/Ag/IPM/manuals.htm and

ENT- 13, Insecticide Recommendations for Soybeans at: http://pest.ca.uky.edu/EXT/Recs/welcomerecs.html

These insects are not very hard to kill. It is most important to detect them before they reach threshold and determine if control is needed. If you find them only after the damage has been done, you can kill them, but you can’t put the foliage back on the plants!