What's Attacking my Potatoes?
Nearly 70 species of plant-parasitic nematodes have been known to wreak havoc in potato fields around the world. The most common nematode species in the Pacific Northwest are root-knot, stubby-root and root-lesion. Several other nematodes, including potato-rot and reniform, also are occasionally associated with reduced potato yields.
Location: Columbia root-knot nematodes, which are sedentary endoparasitic nematodes, are found in abundance, especially in sandy and organic soils. They can be found in localized areas or, in some cases, the entire field.
Symptoms: Above-ground symptoms of Columbia root-knot nematodes are typically absent, but can include a rough and bumpy texture, or galling, on the tuber surface. Brown spots occur on the vascular tissue. Other symptoms include late-season stunting, chlorosis, wilting and nutrient deficiencies.
Damage: Damage from Columbia root-knot nematodes is commonly around 25 percent, but can range from slight to 100 percent. Columbia root-knot nematodes can cause significant damage in both warm and cold climates. Total loss is possible due to tuber marketability. Due to rapid development and number of generations of Columbia root-knot nematodes, the threshold level is one in many growing regions.
Northern root-knot nematodes
Symptoms: Symptoms of northern root-knot nematodes include swelling, galling, stunting, uneven growth and browning within the vascular ring. Brown spots due to nematode presence can be found within ¼ inch of the tuber surface and are typically 1 millimeter in diameter.
Damage: Northern root-knot nematodes infest roots and tubers, causing root injury that severely reduces yields and may accelerate death. Nematodes feed and develop within the galls they create, reducing the ability of the roots to intake water and nutrients.
Location: Stubby-root nematodes, which are migratory ectoparasitic nematodes, are found in isolated sandy, moist soil areas, usually between 8 and 16 inches deep. The mobility of the stubby-root nematode allows it to occasionally travel at depths of deeper than 2 feet.
Symptoms: Symptoms of stubby-root nematodes include irregular-shaped patches in the field, stunting, poor stand, nutrient deficiencies and stubby roots. Feeding by stubby-root nematodes often cause root tips to stop growing, resulting in lateral roots that become stunted themselves. This leads to a series of stunted roots that are incapable of taking up an adequate supply of water and nutrients.
Damage: Stubby-root nematodes, which are differentiated from other nematodes by their curved stylet, cause little direct damage to potatoes, but can pierce root cells and suck out the nutrients. They cause the most damage by acting as vectors for tobacco rattle virus, which causes corky ringspot disease. Damage is greatly influenced by moisture, with increased levels of wetness causing greater damage.
Symptoms: Symptoms of root-lesion nematodes include internal browning, chlorotic foliage, deteriorated roots, premature senescence and early death. High levels of infection can result in reduced root and shoot growth. Lesions are long, yellowish to brownish markings that can resemble cat scratches.
Damage: Root-lesion nematodes are endoparasites that feed and reproduce inside and outside plant roots. All phases can penetrate roots and move from cell to cell, resulting in cell death and brown lesions on the roots. Yield losses can be considerable when high populations are present as root-lesion nematodes (specifically the Pratylenchus penetrans species) weaken potato plants, making them more susceptible to diseases like verticillium wilt. Overall, root-lesion nematodes cause weak, shallow root systems with a significant amount of dead areas.
Source: Idaho Center for Potato Research and Education. Potato Production Systems. 2003.