Nematodes that feed on corn

Nematodes are microscopic worms that live in the soil and water. Many nematode species feed on decaying organic mater, bacteria, fungi, and even other nematodes. But some nematodes, including many that live in the soil, feed on plants and are called plant-parasitic nematodes.


The term corn nematodes would imply that these pests are one uniform group and that they only feed on corn, but this is not correct. There are more than a dozen different species of plant-parasitic nematodes that feed on corn. Most of these also have a wide range of hosts.

Nematodes that feed on corn are not new to the Midwest, these nematodes are believed to have been present since long before corn was a crop in this region. Before corn was a major crop, these pests fed and lived on native plants and prairie grasses

It is common to find these nematodes that feed on corn in almost every field in the Midwest, but populations must reach a certain number called the damage threshold before they are believed to reduce corn yields. This damage threshold varies between species also, for example it only takes 1 sting nematode per 100 cm3 while it would take over 1,000 spiral cause significant damage.

There have been many changes in crop production practices that have been blamed for the increase in nematode damage to corn. These include decrease in soil-applied insecticides, corn frequent cropping of corn, and a decrease in the amount of tillage performed on each acre. While there is no way of knowing that these factors are the cause, we have seen an increase in damage to corn from these pests.

The only way to determine if plant-parasitic nematodes are causing yield loss in your field is to take soil and root sample and have them tested by a qualified lab.

Nothing can be done to minimize the damage or “rescue” a corn crop if nematode damage is confirmed during the growing season. But there are some good management strategies to protect corn from nematode damage in future years. One of these strategies is to use a seed treatment such as Votivo on the seed before planting. Votivo is a very promising new seed treatment that is showing great performance in the Midwest. Please contact you local Trelay DSM for more info on nematodes that feed on corn and what control options are available for your farm.

True Armyworms

True armyworms are showing up in SW Wisconsin and NE Iowa. Armyworms are an occasional pest in the area, but seem to me more numerous than normal is year. Bob Rose and Chris McLimans are both reporting fields with high enough pressures that growers need to take action to prevent stand and yield losses.

This pest will rarely cause trouble in conventional-tilled fields, but growers should be checking reduced and no-till fields. Another likely area of infestation would be fields that had wheat stubble or rye planted as a cover crop that was taken off in the spring. Any kind of ground cover makes a great place for the moths to lay their eggs as they fly up from the south. When the eggs hatch, usually about 7 to 10 days, they begin to feed and will continue for 5 to 6 weeks. At the end of the feeding period they will pupate and reemerge as moths to lay eggs and start the cycle again, we usually see up to 3 generations per year. The second generation will usually appear in July, and is the most damaging.

This insect will usually feed on the leaf margins and will stop at the midrib. Young corn plants have a remarkable ability to recover from the feeding, an ISU study showed that corn in the V7 to V9 stage with 50% defoliation recovered after treatment and only showed a 2-6% yield loss.
Treatment should be considered in V7-V8 stage if larvae are less than 3/4 inch in length, the population is larger than eight larvae per plant, and there is 25% or more defoliation. If armyworms are less than 3/4 inch, they still have about a week to feed before they pupate. At 1 ½ inches, the larvae are about done feeding and treatment is not going to give any economic benefit. There are many common insecticides labeled for armyworm control, you will need to check with your local chemical supplier to see what pricing and availability is for your area.

Sidedressing NH3

Anhydrous Ammonia is a very good source of Nitrogen and also usually the cheapest form available. It is important to make sure you apply the NH3 properly to avoid injury issues.


NH3 is injected into the soil, and usually is the most concentrated within 4” or so of the knife track. In sandy soils or very dry field conditions the concentrated band will be larger because NH3 has a huge attraction to water, and it will move to find available soil water. If you run the knife too close to the rows, you could see root injury from the applicator knife, but there is an even greater risk of burning the roots of the plant from the NH3 itself. See the picture below of root “burn” from NH3.

Once the NH3 ties up with soil water, it moves with soil water to the plant roots and can be taken up and used without causing any injury problems.


Another way NH3 can cause injury is by burning the leaves above ground. In very wet soils the knife will seal the sidewalls so the NH3 cannot move into the soil profile. This will cause the NH3 to move back up the slot made by the knife and escape into the air. Not only will you loose the NH3 that you are applying, it will burn the leaves of the young corn plants. Usually the corn will recover, but the Nitrogen that escapes is lost and does not available for the plant later in the season when it needs it most. It’s always good to make sure soil conditions are good and that you are getting a good seal in the knife tracks when applying NH3.

Frost Damaged Soybeans

Now I would like to talk a little about the differences between how soybeans react to frost as opposed to corn. In the last post I talked a little about frost damage on corn. And because of the way corn grows, a frost early in the season usually doesn’t cause serious problems. When we look at soybeans the game changes, soybeans don’t have the protection from frost that corn does because the growing point of the soybean plant is exposed as soon as it emerges. Just like we talked about with corn, the best thing to do with soybean is have a little patience to see if the individual plants will survive. This picture shows what to look for when assessing frost damage on soybeans.

If the plant was damaged by frost below the cotyledonary node, it will not survive. But if the plant was injured by frost, but only down to the area above the cotyledonary node, the plant will be able to generate new growth from the auxiliary buds at the node. This new growth from these buds will be very similar to the original plant if it had not been damaged. Recovery will be good with little or no impact on final yield. If there are a mix of plants that will recover and several that are frosted and will not survive it is important to take stands counts from many areas of the field to determine the next step. We may find some areas that are hurt more than others, but the number I use to make decisions on replant is 100,000. If you have at least 100,000 plants an acre it is too good to justify the cost and time to replant. if replant is needed try to identify if you can fill in areas of the field, or if it is best to tear it up and start over. And just like corn, this crop has been stressed, so make sure you give it time to recover before you add any more to it with herbicide applications.

Frost Damaged Corn

The past weeks weather has slowed the great progress we have seen with planting and crop emergence. Some areas even experienced snow and frost, so I am going to give you a few thoughts on what this means if you were in one of these areas. First we need to look at how corn grows, when corn emerges the growing point of the plant is still well below the soil surface. In fact the growing point does not reach the soil surface until the plant reaches v5 to v6 growth stage. That means that at least 5 full leaves are developed and you can identify the leaf collar on the plant.

Fortunately most of our corn was not at the v5 stage yet. If you did experience some frost on smaller corn the best thing to do is wait and watch. The frosted leaf tissue will turn yellow and start to wilt as it turns brown and begins to decay over the next week. If you dig some plants and split them open you will see that the plant material below ground will be white and firm, this is a good sign and tells you that the plant is alive and will recover with the return of warm weather. The plant will continue to grow and push up through the damaged tip, as it does so its important to watch and make sure the new growth is able to open the new leaves to collect sunlight and recover. In some rare cases I have seen where it helps to clip the frosted tips off to enable the new growth to come through, but this is rare. From here forward the crop will recover, but it’s important to remember that it has been stressed, so make sure we do not do anything to add to the stress; like apply any herbicides for a few days.

Plant by Soil Temperature, not the Calendar

Planting is moving fast this year, with most areas of the Midwest way ahead of last year and the five year average according to USDA crop progress reports. Planting early can help to maximize yield potential along with allowing more time for the crop to mature this fall. Here is an article that quotes Dr. Bret Bean, Extension Agronomist from Texas. Many of the things he notes also are important for growers here in the upper mid-west. Click here to read the full article. 

Assessing Alfalfa Stands

Now is the time to be looking at your alfalfa fields to make stand evaluations. Even though we had good snow cover this winter, it is still important to look at your fields this spring before you finalize your cropping decisions. By evaluating stands now you will be able to make decisions about what fields to save, what fields are getting thinner and need to be replaced soon, and what may need to be rotated to another crop this year.


The best way to valuate you stand is to look at the above ground part of the plant first. Check to see how many shoots you have in a square foot, over 55 stems per square foot is ideal, 40-55 means yields may be reduced, and under 40 means the stand is poor and may need to be replaced. Look to see that the shoots are coming from all sides of the crown and not only one side. Check for crowns that may have heaved up over winter or do not show any new shoot growth.

Also be sure to dig some roots and check to see how healthy the crowns are. Healthy crowns and roots will look white to cream colored and will be firm. If the crowns are discolored they may be infected with some root rot diseases that will limit production.

Talk to your Trelay DSM if you have questions or would like help in evaluating your alfalfa stands this spring to make sure you get the most from every acre that you farm.