Diagnosis and Management of Nematodes in Corn
Nematodes, also known as roundworms, are a phylum of nonsegmented invertebrates that are the most numerous multicellular animals present in soils and plant tissues. Although their numbers can easily exceed 10 billion per acre of soil, the importance of nematodes is often overlooked due to their small size (most are less than 1/25 inch in length). Many species are beneficial, either because they feed on fungi and bacteria, accounting for a significant amount of nitrogen mineralization in the soil, or as parasites of insect pests. Other species, however, are parasites of plant roots and, in some cases, can severely limit crop production. There are over 60 plant-parasitic species associated with corn in North America (Norton, 1983). The most common nematodes encountered in commercial corn fields in the North Central Region are listed in Table 1. During feeding, these nematodes puncture plant cell walls with a hollow stylet and secrete digestive enzymes into the cell. Injury results from wounding and from toxicity and enzymatic activity of the secretions.