Lesion or root-lesion nematodes comprise over 40 species of Pratylenchus and several are important for potato production. This group of nematodes is found in all potato-producing areas in North America and Canada. The most common species found in the U.S.A. are P. penetrans and P. neglectus.
|Root Lesion Nematode|
Eggs are laid in the soil or on roots and may be found clumped in small groups. Generations range between four and eight weeks depending on soil temperature and type. P. penetrans like soil temperature below 76 F. These nematodes are worm-like in all juvenile stages and in both sexes of adults. All juvenile stages and the adults can attack roots. When the soil is wet, these nematodes move little and when dry, they may become dormant. Lesion nematodes usually overwinter in soil as late-stage juveniles or adults.
Symptoms and Damage:
High population density of lesion nematodes can cause vine growth to be retarded showing poor vigor. Stunting may be observed. Leaves may show some yellowing. Severe infestations can lower yields by the production of undersized tubers. Lesion nematodes feed primarily on roots causing small elliptical lesions or cuts. Lesions may be quite small (1 mm or 0.04 inch) and on tubers, lesions may be large enough to appear like warts. Feeding on tubers and stolons is uncommon but has been reported. The primary problem with lesion nematodes is that these lesions form a portal or opening through which soil pathogens can enter. The most notable and common pathogen associated with lesion nematodes is the fungus Verticillium dahliae. Especially P. penetrans will synergistically increase the effect of V. dahliae (Verticillium wilt also commonly referred to as early dying). Therefore, when both the nematode and the fungus are present in the field even at below effective populations, early dying may become quite noticeable and economically deleterious by reducing yield.
Lesion nematodes spread readily in contaminated soil via seed tubers, equipment, storage, wind, and animals. Host resistance to them is not yet commercially available but is being researched. The host range for lesion nematodes is very extensive, over 160 hosts, and includes both grasses and broadleaf plants including crops and weeds. Due to the wide host range, crop rotation is not generally effective as a means of control. Corn and other grain crops, and alfalfa are favorite hosts. If nematode populations are low, cover crops such as ryegrass or canola used as green manures could be used to inhibit population build up. Economic thresholds for lesion nematodes have been established in potato fields in some places such as in the Columbia River Basin. Soil fumigation is the most common practice used on fields known to be infested with both lesion nematicides and Verticillium dahliae, and a history of early dying. A few non-fumigant nematicides are available for lesion nematode management but to be effective the species must be identified.
Nematodes in Potato: