Cotton root showing galling by root-knot nematode

Soybean root that is badly galled

Root-knot damage to a cotton field

The dry weather really shows areas in fields that have been damaged by plant nematodes. Plants that are already weakened by the presence of nematodes simply cannot handle the additional stress produced by drought.

Root-knot nematode has been particularly linked with dry weather. This nematode causes considerable disruption of the normal root system through the production of galls. Galls are a swelling of the root around the area where the nematode has penetrated. Galls vary in size depending on the plant host and number of nematodes that are present. A few galls really don’t seem to hurt plants.  Lots of  galls can cause severe injury.  Damage shows up a stunting, early wilting during drought, loss of yield and early death.

Reniform nematode has been increasing rapidly in Louisiana during the past 15-20 years. This nematode seems to cause the greatest damage in years where drought occurs. When there is plenty of rainfall, damage is usually light or not expressed by reniform nematode. Exceptions might be when there are extremely high populations of the nematode. Reniform nematode doesn’t produce galls and is extremely difficult to identify except through a soil sample.

Producers should be watching out for areas in fields that are stunted or just yielding poorly. Although nematode injury really shows up during drought, this may not be the best time to sample to check for nematodes. These areas should be flagged or marked with handheld GPS receivers so that they can be found later when adequate moisture is present for sampling. Nematode samples should be sent to the Nematode Advisory Service offered by the LSU Agricultural Center.