Root-knot Nematode

Penstemon infected with
root-knot nematode
(Photo: NMSU-PDC)

Featured Diagnosis: Root-Knot Nematode (Meloidogyne incognita) on Penstemon pseudospectabilis.

Key symptoms: Weak, stressed, dehydrated plants with galls (or knots) on the roots. This nematode causes damage on a wide range of host plants including many ornamental plants, agronomic crops and vegetables.

Root-knot nematodes are microscopic, non-segmented worms that are free-living in the soil as a juvenile. When the nematode infects a host plant, the adult becomes sedentary, feeding in one location in the root. The primary symptom of root-knot nematode is the formation of galls or knots on the root system. The galls or knots are a combination of the female nematode and "giant cells" which develop as a result of nematode feeding.

Galls on roots caused by
root-knot nematode
(Photo: NMSU-PDC)

Damage to infected plants results from the inability of water and nutrients to move up through the knots, resulting in above-ground symptoms similar to those caused by many root-infecting pathogens or environmental factors that reduce water uptake by the plant. Infected plants are generally stunted and have fewer, small, pale, off-color leaves. Infected plants may wilt during the hottest time of the day and recover at night. When plants ar infected in the seedling stage, the result may be plant death. However, when mature plants become infected, plants usually do not die, but they are unthrifty and usually produce fewer flowers and fruit than uninfected plants.

Unfortunately, there are limited control options for root-knot nematode in residential environments. Soil solarization can reduce the nematode population. Rotating the garden to a new location and the use of resistant or tolerant varieties can also help to reduce losses.