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Symptoms and Signs

Plant Roots:
Symptoms of lesion nematode disease (as with most nematode-induced diseases) often go unrecognized initially because the nematodes (Figure 1) are microscopic pathogens of belowground plant parts (mainly roots), and the aboveground symptoms are often general symptoms of plant root stress. Low to moderate populations of lesion nematodes may cause no visible aboveground symptoms. On well-managed turf and in some woody ornamentals the only symptoms are a lack of winter hardiness. High nematode populations and infection of young plants can lead to stunting, nutrient and water deficiencies, and eventual dieback. Only when the nematodes are extracted from soil and infected plant parts (i.e. roots) (Figure 2) can they be identified under a microscope to confirm a lesion nematode diagnosis.

Figure 1

Figure 2

As their common name implies, lesion nematodes produce characteristic necrotic lesions (darkened areas of dead tissue) on the surface and throughout the cortex of infected roots (Figure 3). The lesions turn from reddish-brown to black and are initially spotty along the root surface. As the nematodes continue to migrate and feed within the roots, the lesions can coalesce to become large necrotic areas of tissue that may eventually girdle the root (Figure 4). Tissue distal to the lesion is frequently sloughed off. Severe damage from high populations of lesion nematodes can result in a stunted and necrotic plant root system (Figure 5). The extent of lesion formation can be accelerated during concomitant root invasion by other soilborne plant pathogens, and sometimes these interactions can develop into synergistic disease complexes. Lesion nematode damage to roots not only causes losses in yield (Figure 6), but also can cause losses in marketable quality of infected plant products (Figure 7).

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Potatoes:
The interaction of lesion nematodes (mainly P. penetrans - Figure 8) and Verticillium wilt fungi (mainly V. dahliae) results in a disease complex known as "potato early dying syndrome" that has become of increasing economic significance within the last decade. This syndrome can lead to premature vine death and severe yield losses that can become a limiting factor in potato production (Figure 9). Lesion nematodes can also infect potato tubers and, depending upon the species, can cause a scabby appearance with sunken lesions or dark, wart-like bumps that turn purple on tubers in storage.

Figure 8

Figure 9

Peanuts:
Although lesion nematodes can infect peanut roots and cause plant stunting and chlorosis, they are more often associated with damage to peanut pods and pegs ("stems" that extend underground to form the pods). Lesion nematodes (P. brachyurus in the southern U.S.) initially form small brown tunnels in peanut shells that expand into purplish-brown lesions with distinct boundaries (Figure 7). Extensive lesion formation, and pod and peg rot, can occur with concomitant invasion by other soilborne pathogens.

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