Do I Have Nematodes?

Nematodes are microscopic worms that feed on the plant tissue and root system of potatoes. They can remain stationary or move through the soil, and can live either inside or outside of roots, impairing the root function. By reducing the root's ability to uptake water and nutrients from the soil, nematodes cause poor growth, low yield, deficiency symptoms, a poor root system and cosmetic damage to the sellable crop.

There are two basic types of root-parasitic nematodes: endoparasitic and ectoparasitic. Endoparasitic nematodes enter and feed within the root system, and include root-knot, lesion and cyst nematodes. Ectoparasitic nematodes feed exclusively from outside of the root tissue and include stunt, stubby-root and sting nematodes.

Symptoms
Typical symptoms of nematode injury can involve both above-ground and below-ground plant parts. The following are symptoms of a nematode infestation:

  • Galls on the roots and cosmetic defects on the surface of the potato
  • Stunting and reduced vigor
  • Sunken, dark-colored pits or skin cracks
  • Poor root development and plant uniformity
  • Premature wilting
  • Slow recovery to improved soil moisture conditions
  • Leaf chlorosis (yellowing)
  • Brown spots within vascular ring

Plants exhibiting stunted or declining symptoms usually are found in patches of nonuniform growth as opposed to an entire field exhibiting an overall decline of plants.

Injury symptoms in potatoes are related to the type of nematode, nematode population density, crop susceptibility and current environmental conditions. For example, under heavy nematode infestation, growth of young plants may be restricted and, therefore, could develop a stunted condition.

Under less severe infestation levels, symptom expression may be delayed until later in the season – after a number of nematode reproductive cycles have been completed. In this case, above-ground symptoms will not always be apparent early in crop development. Symptoms will become more pronounced over time, and reduction in root system size and function may be experienced.

Plant symptoms and yield reductions may be directly related to preplant infestation levels and other environmental stresses imposed upon the plant during crop growth. As infestation levels increase, so then does the amount of damage.