A recent Wallaces Farmer article shared that in the last two weeks, soybean fields have been reporting cutworm damage – an unusual phenomenon since cutworm is commonly known as a corn insect pest.

Cutworm damage in corn is reported almost every year in Iowa, Erin Hodgson, an ISU Extension entomologist said, but infestations are patchy and sporadic because the cutworm moths have to migrate into Iowa from the Gulf Coast or from the far southern states such as Texas every spring. The moths are attracted to fields where there are young weed seedlings and the cutworm moths lay eggs in these fields. The eggs hatch to produce the larvae (worms, see image) which chew on corn leaves and can cut off young corn plants.

Cutworm damage in soybeans, however, is not typical. Hodgson says entomologists don’t fully understand why cutworms sometimes cause damage to soybean plants. She said there are a few field conditions that may make soybean fields attractive to female cutworm moths:

• Fields planted under reduced or no-tillage practices
• Fair-to-poorly drained fields
• Fields with winter annual weeds emerged prior to soybean planting
• More likely found in fields previous infested with cutworms

Determining Cutworm Damage

Hodgson recommends checking 20 consecutive plants in five different areas of your field to determine the percent of cutworm damage. Young cutworms may feed on the soybean stem or leaves, but older larvae can clip off cotyledons. Look for discolored, wilted or dead plants. Cutworms will seek shelter during the day, so dig 2-3 inches down in the soil within a row to try to find them. Consider an insecticide if larvae are less than3/4 inch long and more than 20 percent of plants are damaged or missing.

Click here for the full article.

Clipped or missing plants could be a sign there’s a new scavenger in your emerging soybean fields, according to a recent article in Wallaces Farmer.  Isopods – a.k.a. woodlice, pillbugs, sowbugs and roly-polies – are a new early-season soybean pest in the Midwest.

No-till fields can be especially attractive to isopods as the crop residue helps provide high levels of moisture needed for their survival. Because all life stages breathe through gills, isopods must live in habitats with high humidity.

These omnivores scavenge on dead and decaying plant or animal matter but will also eat live, young plants. Feeding is often done at night as isopods are skittish.

Although small in size (adults are three-eights inches long), isopods can do big damage.  Some areas in Kansas and Nebraska have already experienced economically damaging levels of isopods that required replanting.

Management is difficult as these terrestrial crustaceans are naturally protected by armor-like plates on their backs.  Seed treatments and foliar insecticides have been ineffective. To minimize overwintering populations and to reduce soil moisture in the spring, Extension crop specialists are recommending to till heavily infested areas every other year.  Click here for more information, including photos of affected seeds and seedlings.

Wallaces Farmer shared an article recently including points to consider when collecting samples for nematodes in strip trials. The article stated many people have asked how to properly collect nematode samples from strip trials of corn treated with new seed-treatment nematicide products – the two most common being Avicta Complete Corn and Votivo.

Greg Tylka, an Iowa State University Extension plant pathologist and nematode expert said to consider the following when gathering samples for nematodes in strip trials.

• The new seed-treatment nematicides provide early season, not season-long, nematode protection; duration of protection is not specified or known. Differences in nematode numbers due to the nematicides may occur early in the season (four to six weeks after planting), when the nematicides are having an effect, and not later in the growing season.

• There are many different species of corn nematodes and they vary in their generation times. For example, the root lesion nematode can complete a generation in 30 to 50 days; dagger nematode will have only one generation in an entire growing season. The likelihood of detecting a difference in nematode numbers among treatments depends on what nematodes are present in the field and when the nematode samples are taken.

• Soil and root samples should be collected to assess nematode numbers. Roots are needed because some plant-parasitic nematodes feed almost entirely inside corn roots during the growing season; their numbers can be deceivingly low in the soil. Whole plants can be submitted if plants are relatively small; otherwise, root balls should be submitted. Collect several plants or root balls from each sampling area or “plot” so nematodes can be extracted from root tissue.

• It is difficult to determine where to collect samples from strips. One suggested method is to collect 20 of the 12-inch-deep soil cores and a few plants or root-balls from a four- or eight-row wide by 25- to 50-foot-long area of each strip. The sampled area will serve somewhat like a plot for each treatment.

• Collect sets of samples from “plots” in a straight line (or transect) across the various treatments in the strips. Ideal places to locate the transects in the field include: 1) areas suspected of having damaging nematode populations, 2) areas where there is poor corn growth and 3) areas with uniform soil conditions (and hopefully uniform nematode populations).

• Soils with higher than 70% sand content can be infested with needle and sting nematodes, and these nematodes can be difficult to recover in the middle of the growing season. If needle and sting nematode infestations are suspected, you should collect soil samples from strip trials within the first four to eight weeks of the season. With these nematodes, there is no need to collect root samples as both species exist exclusively in the soil. Collect several plants or root balls from each sampling area or “plot” so nematodes can be extracted from root tissue.

Click here for the full article. Tylka will be providing additional information on corn and soybean nematodes at the Latham Country Fair in Alexander, Iowa, July 30. Please watch the blog for more details!

If you have any questions about how to sample strip trials for corn nematodes, simply click “Leave a comment” and comment in the field box we’ll answer your question shortly.