Charles Overstreet, Xavier, Deborah
Wheat is one of the few crops that we grow in Louisiana that does not have serious nematode problems. However, there are a number of nematode pests that can be associated with wheat. The southern root-knot nematode (Meloidogyne incognita) is one pest that has some potential for causing problems.
Root-knot nematodes attack the roots of wheat, forming small galls in the area around where they begin feeding. Typically, these galls are not visible until late in the spring and may be associated with chlorotic and stunted plants. Most of the time when root-knot nematode is present, there are not any noticeable foliar symptoms.
Southern root-knot nematode is greatly impacted by temperature and is not very active in the soil once soil temperatures drop below 65°F. This nematode is adapted for our hot summers where it causes serious problems for many plants. There is only a short time in the fall and late in the spring when soil temperatures are warm enough for these nematodes to be active. Under favorable conditions for the nematodes, they move into the roots within a few days of emergence. The life cycle is fairly long during this winter phase, taking several months to complete. There usually is only one life cycle on wheat compared to 4-5 on a crop grown during the summer months.
Although we don’t think that we suffer serious damage to wheat from root-knot nematode, the greatest problem may be with the subsequent crop. Root-knot nematodes decline dramatically during the winter months with only about 5-10% of the fall population surviving to attack the next crop. Although root-knot nematode may increase on wheat, population levels are still much reduced from the initial fall levels. However, the root-knot population will be higher after wheat than on fallow ground. The increased population in the spring may cause greater injury to any susceptible crops that are planted next. Soybeans are one of the primary crops grown in association with our winter wheat and are readily damaged by these nematodes.
Management of root-knot nematodes usually is limited to cultural methods. Because of the temperature influence on root-knot development, planting date appears to be the best method of limiting problems. Delaying planting until near the end of the planting season will prevent any infection by the nematodes during the fall. Since the wheat crop will be almost mature before soil temperatures are warm enough for nematode development, little if any damage will occur in the spring. Currently, there is not much research being conducted to develop wheat varieties with resistance against root-knot nematode.
Healthy seed and infected galls of the wheat nematode. Photo from Nemapix.
In the past, the wheat nematode (Anguina tritici) was an important pest of wheat. The wheat nematode is unusual in that instead of attacking the roots of plants like the previous nematode, it attacks the growing point and particularly the flower buds. As soon as the nematode attacks the flower, it develops a gall instead of normal seed. These dark, black galls may contain 10,000-90,000 juveniles. The juveniles remain in a dried state after harvest until the galls are planted with the next wheat crop, starting the nematode cycle again. The nematodes in these galls have been known to survive for 25 or more years. Modern harvesting and cleaning systems have eliminated this nematode pest in the U.S.