Plant Parasitic Nematodes in Corn
Plant parasitic nematodes are microscopic organisms that require living host plant tissue to feed on in order to grow and reproduce. They live in the soil and feed in or on the corn plants root system. These nematodes can be found in just about every cornfield to varying degrees. There are several species that can affect corn roots, with common names like Lesion, Lance, Stunt, Sting, Stubby root, Root-knot, Needle, Dagger, Root-lesion, and Spiral. Whether they cause significant crop injury and/or yield reduction is determined by which species are present in the field and the population density. Some species populations can be lowered and many just simply maintained with a crop rotation to soybeans, dry beans, cotton, alfalfa, or small grains, but continuous cropping of corn can cause an increase in nematode populations. Corn yield losses, caused by nematodes, can sometimes go undetected, and may be attributed to low pH, high pH, nutrient deficiencies, soil compaction, herbicide carryover and other problems. Nematode sampling, identification and subsequent management are essential to protecting corn yield potential.
Figure 1. Yellowing of corn plants cause by root-lesion and other plant parasitic nematodes. (Photo from University of Nebraska – Lincoln)
Figure 2. Damaged roots near the end of the growing season in same field. (Photo from University of Nebraska – Lincoln)
Figure 3. Severe sting nematode injury (Photo from University of Nebraska – Lincoln)
Figure 4. Severe damage to root system by sting nematodes (Photo from University of Nebraska – Lincoln)
How do you Manage Plant Parasitic Nematodes?
- Management begins with multi-year rotations with non-host crops. You will find a list of non-host crops on the action sheet that follows the Midwest Laboratories diagnosis report. Also, there have been some new options with seed treatment nematicides that can provide some alternatives for plant parasitic nematode management. Contact your local agriculture retailer or extension service for questions about these options.
Sampling Procedure for plant parasitic nematodes:
- The procedure for sampling a field depends on whether you are sampling for diagnostic or predictive purposes.
- Predictive: Perhaps your corn yields have dropped off in recent years but you have attributed the yield loss to nutrient deficiency or pH extremes. This type of sampling can be done at any time after the previous crop has been harvested and the next crop is planted. Predictive sampling will assist you to determine if nematodes will become a problem for the next growing season. Ideally, you would want to divide the field into several sampling areas of roughly 5-10 acres each. Collect 20-30 soil cores at a depth of 8-10” for each area and place in soil bag for shipment to Midwest Laboratories. Predictive sampling can be done on medium to fine textured soils to identify most species of nematodes, which aren’t known to travel much deeper than 8-10”. However, predictive sampling would not be recommended on course textured sandy soils (80% sand) as species such as sting and needle nematodes can begin moving deeper into the soil profile after early plant growth (V6) and can be missed by the soil probe in the fall or early spring. Also, we would recommend that predictive nematode samples be taken separate from any fertility soil samples in the fall or early spring.
- Diagnostic: During the growing season, you may see circular or oval areas of stunted and or yellowed corn plants, usually in small areas of the field, but may include larger areas. It is important to understand that the highest nematode counts will most likely be at the edge of the damaged area rather than in the middle. For this reason, we recommend taking samples on the perimeter of the stunted areas where plants are still in good health.
Procedure for sampling for plant parasitic nematodes:
- On sandy soils, take samples up to V6 growth stage. All other soil types can be sampled throughout growing season, although up to V6 is preferred.
- Take at least three root mass samples by digging up the entire plant with as much soil intact as possible around the root system and place in a sturdy sealable plastic bag. If sampling in medium to fine textured soils and samples are taken after V6 growth stage, you can cut the corn plant off near the base and send the three root mass samples in a sturdy, sealable plastic bag.
- In addition to the root mass samples, collect approximately 20 core samples at 8-10” deep and mix roughly two cups of soil for a separate soil sample.
- Be sure to probe at an angle through root zone.
- Keep samples in a refrigerator or at least room temperature until shipping.
- Handle all samples with care. The reliability of the diagnosis is only as good as the sample you submit. The nematodes must remain alive from the field to the laboratory in order to have an effective analysis.
How do you ship them to the lab?
- We would recommend shipping the same day of sampling and ship overnight if possible.Midwest Laboratories has very competitive overnight shipping options from anywhere in the United States.
- Ship samples early in the week. Please contact Midwest Laboratories (402) 334-7770 or your field representative for shipping options.
- Place samples in a cooler or plastic lined box with frozen ice packs sealed in sturdy, sealable plastic bags. Keep in mind, the shipping time and outside air temperature before shipping your samples.
- Complete a pre-printed Midwest Laboratories plant parasitic nematode submittal form. The submittal form can be obtained by contacting Midwest Laboratories at (402) 334-7770 or download the form at midwestlabs.com. You can also copy and paste the link below
- Please include a copy of the Midwest Laboratories USDA/APHIS permit to move live plant Pests in soil.
- Contact George Nelson at Midwest laboratories (402) 829-9868 or your field representative to obtain a copy of this form or copy and paste the link below.
What are the turnaround times for results?
- The turnaround time of your results for plant parasitic nematode sample assays are generally 7-10 business days after receipt of the samples. This TAT may be extended during planting and harvest seasons. Sample results will be reported by genus and numbers/100 cubic centimeters of soil. The results will also give totals for each parasitic plant nematodes recovered. Along with the report, Midwest Laboratories will include a descriptive action sheet to assist you in decision-making moving forward.
For more information visit our website at www.midwestlabs.com or call your field representative at 402-334-7770.