In the Midwest, corn production practices have drastically changed. These changes have also brought an increase in damage from plant-parasitic roundworms or nematodes. Nematodes are often found in drier, sandy soils. Fields may have poor or uneven stands. Corn plant may appear yellow and stunted and have small or poorly filled ears. Wilting at midday may occur. Root damage depends on the species of nematode. Symptoms can occur at anytime and are usually spotty throughout the field where high concentrations of these roundworms are present. Every corn field in Iowa has nematodes of some sort feeding on roots. The most common include dagger, lesion, and spiral nematodes. Damage is determined by nematode species, population densities, and environmental conditions.
Environment and Scouting:
Lack of moisture and poor fertilization will contribute to greater nematode damage. The best time to scout is when symptoms of damage are observed, no later than R3. Collecting 15 to 20 soil cores from the root zone of the symptomatic plants and collecting a few root systems when the plant is at stage V6 or younger. Damage is most common in dry sandy fields.
Depending on the species, nematodes may feed on the outside (Ectoparasitic) or on the inside(Endoparasitic) of the root. Crop injury can be severe when nematodes feed on roots early in corn development. Above ground symptoms of nematode injury appear in patches within the field. Symptoms include stunting, yellowing, and wilting and lead to yield loss. The roots can be pruned, discolored, and swollen. Sometimes plants can be infected but not show any symptoms.
Maintaining good soil fertility will minimize the likelihood of nutrient deficiency which can predispose plants to nematode injury. Tillage and crop rotation can be useful strategies for reducing some nematode populations. Management options are dependent on the species of the nematode. Many nematodes can live up to 2 years and can infect other plants making crop rotation difficult. Nematodes will die quickly though if a host plant is not present.