Issue No. 7, Article 6/May 7, 2004
Time to Look for Corn Nematode Injury
In Illinois, when most people speak of "corn nematode," they mean the needle nematode. Needle nematode is one of the few plant-parasitic nematodes that can seriously reduce corn stands, so it isn't any wonder that producers are concerned about it. Remember, though, that needle nematode is found only in soils containing 80% sand. In heavier soils, other nematodes are to blame for corn injury.
Symptoms. Depending on the number of nematodes in the soil, needle nematodes can reduce seedling growth or even kill seedlings. The symptoms will not be distinctive, and you could easily decide they are due to other causes. The time to suspect needle nematode is when you see patches in the field where emergence is uneven or seedlings are stunted. When you see this kind of damage, get an expert diagnosis. (True, there isn't anything you can do about the nematode once the damage shows up, but you won't be able to protect your crop from damage the next time you plant corn if you don't know the identity of the pest. Remember, the nematode population--and the potential for damage--will only increase.)
Diagnosis. Needle nematodes are very large compared with other plant-parasitic nematodes, but because they are so thin, they can't be seen with the naked eye in soil. The only way to confirm a needle nematode diagnosis is to submit a soil sample to a qualified laboratory for analysis (for example, see the University of Illinois' Plant Clinic Web site at http://plantclinic.cropsci.uiuc.edu/).
You'll need a soil probe or a small shovel, a bucket, plastic bags (quart-size Ziploc bags work well), a permanent marker, and a cooler. Collect soil from the root zones of 10 to 20 different plants at the outer edges of an affected area. Sample as deeply as you can comfortably, and discard any dry soil from the upper profile. Don't sample where plants are dead. Nematodes must feed on living plants, and they'll move away from dead ones. Mix all the cores together in the bucket, but be gentle! Fill a quart-size plastic bag with soil from the bucket; and immediately seal the bag, label it with the permanent marker, and place it in a cooler. Allowing the soil to dry out or heat up will kill the nematodes and reduce the reliability of your sample.
Management. If sampling confirms that you have a needle nematode problem, there are several things you can do to reduce it.
- First, rotate to soybean or another dicot, and be diligent about grassy weed control. Needle nematode can feed very well on many different grasses.
- Second, a nematicide can be applied. Check with the Illinois Department of Agriculture Web site for pesticides labeled for nematode control (see http://www.agr.state.il.us/; click on > environmental issues > pesticide use & registration > registration searchthen search for nematicides).
- Third, try tillage. We have not tested this approach for needle nematode management, but there are several reasons that it might be useful. We see some of the more severe problems in irrigated corn-on-corn no-till fields. Needle nematodes belong to a group of nematodes that are sensitive to tillage operations. Again, this approach has not been tested for its effect on needle nematode problems in Illinois, but it might be worth a try if needle nematodes are threatening your corn crop.
For further information, contact me at (217)244-5940 or firstname.lastname@example.org. --Terry Niblack