Raspberry root lesion nematode

Cause. The root-lesion nematode Pratylenchus penetrans is a migratory endoparasite where part of the population is in soil and part in the roots at all times. Populations in raspberry generally are low through winter and spring, increase rapidly through the summer, and decline in fall. Densities at or below detectable levels at planting can increase to damaging levels by the sixth-to-eighth year. Other species of this nematode do not cause significant root damage. Most of red raspberry varieties commonly planted in the PNW are good hosts for this nematode.
Symptoms. Small, elongated, discolored lesions appear on new roots of infected plants. The fine-feeder roots die as the damage increases. This damage stimulates the formation of many fine roots and a witches' broom appearance. Without feeder roots, the larger diameter roots are unable to take up nutrients and water and often are invaded by secondary fungi. Aboveground symptoms are most often observed on fruiting canes and include reduced cane number and diameter, stunting, and off-color leaves.