Nematodes attacking soybeans

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.    

Soybean is host to many types of plant-parasitic nematodes. Obviously, the nematode that demands the most attention is the soybean cyst (SCN). SCN is a major limiting factor in the production of soybeans worldwide and is estimated to cost U.S. soybean producers over 1 billion dollars annually. However, because of its importance, other nematodes are often ignored.

Northern root-knot, lesion, lance, dagger, stunt, pin and spiral nematodes are found in soil samples collected from soybean fields in Michigan. Of these, only root-knot nematodes are regarded as serious pathogens of soybean worldwide, ranking in the top 10 of most important soybean pathogens. In our state, however, the northern root-knot nematode is infrequently (less than 25% of samples) detected in soil and root samples. This is probably due to the fact that soybean is often rotated with field corn or small grains and these plants are non-hosts for the northern root-knot nematode. Virtually all other types of plants will host this nematode, and it is a serious problem in vegetable, fruit and landscape plant production. The damage threshold for the northern root-knot nematode is unknown for Michigan but is estimated at 500 second-stage juveniles (J2s) per root and soil sample.

Lesion nematodes are common (25 to 75% of samples) in samples collected from soybean fields. These nematodes are not regarded as serious pathogens of soybean, but anecdotal evidence suggests their feeding will result in the production of symptoms including yield loss in Michigan. They are typically found in high population densities on soybean when soybean cyst nematode is absent. As SCN numbers increase, lesion nematode population densities often decrease. Lesion nematodes are a concern because they feed on virtually all species of cultivated plants. In addition, they can predispose plants to invasion by other soil plant pathogens that inhabit the soil. The damage threshold for lesion nematode in Michigan is estimated at 300 per root and soil sample although lower numbers have been reported to damage soybeans in the southern United States. As mentioned, lesion nematodes can reduce yields of other field (row) crops, so they should be closely monitored and managed.

Lance nematodes are infrequently (less than 25% of samples) found in soybean samples collected from Michigan. They are rather large nematodes and are considered fairly serious pathogens of soybeans in the southern United States where the damage threshold is reported to be 4-100 per 100 cm3 soil. In Michigan, we estimate this threshold at 125 per root and soil sample. Lance nematode is also an important pathogen of corn.

Dagger nematodes are not considered important pathogens of soybean in Michigan. They are often found in high numbers on corn, and damage has been observed at population densities above 250 per 100 cm3 soil. Many grass species appear to host dagger nematodes. These nematodes are important in fruit production because they vector some very important plant viruses.

Stunt nematodes are similar to daggers in that they are largely insignificant on soybean but can reduce corn yields. They all do very well on many grass hosts. They do not vector plant viruses. Pin and spiral nematodes are common in soil samples collected from fields in Michigan where field crops have been grown. Neither is regarded as a pathogen of soybean. Anecdotal evidence suggests that pin nematodes can retard growth of sugar beet in our state. High population densities of spiral nematodes are, on occasion, associated with stunt corn plants.

When root and soil samples are collected from fields and submitted for nematode analyses to Diagnostic Services at MSU, all genera (cyst, root-knot, lesion, etc. are common names of nematode genera) of plant-parasitic nematodes are identified and counted. For samples submitted using the MSPC-sponsored SCN program or sentinel plots, risk ratings will be assigned for all nematodes on soybean. Nematode risk ratings are as follows: 0 = none; 1 = low; 2 = moderate and 3 = high. Management recommendations will also be included.

Additional information regarding nematodes on field crops can be found in MSU Extension Publication E-1582, Insect, Nematode and Disease Control in Michigan Field Crops or any of the MSU publications on field crops ecology. For questions, please call me at 517-432-1333, Dr. George Bird at 517-353-3890 or Angela Tenney at 517-353-8563.

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