Root knot nematodes (Meloidogyne) are widespread plant parasites that cause considerable damage to the cultivation of potatoes, carrots or salsify.
Spreading
Root-knot nematodes are mainly present on sandy and sandy loam soils. They have a wide range of host plants and can multiply very rapidly. Introduction of root-knot nematodes occurs through the importation of infected soil, plant material or in irrigation water. Prevention should be the first line of defense. If, however, nematode populations do establish in a field, further propagation must be prevented, and existing populations need to be eradicated.
Pest symptoms and economic impact
Meloidogyne chitwoodi and Meloidogyne fallax cause damage in crops such as potato, carrots, black salsify, and certain flower bulbs (gladiolus – dahlia). Reduction in yield is rarely observed. Their presence has however strong financial impact as they make these crops often commercially unacceptable. In sugar beet, they can reduce plant stand. Meloidogyne incognita and Meloidogyne javanica, do impact normal sugar beet root development.
Above ground symptoms on sensitive crops are often absent. Below ground, root-knot nematode is confirmed by the presence of knots (galls) on roots and tubers. The extent of the damage depends on cultivar, population density, temperature, and growing season length.
Presence in potato seed tubers, dahlia and gladioli bulbs leads to refusal of the plant passport or phytosanitary certificate required for movement within or outside the EU.
Control
Control of root-knot nematodes can be achieved by such means as black fallow or inundation. However, this is far from feasible on all plots.
A well-considered crop rotation, involving population-reducing crops before the cultivation of susceptible crops and the inclusion of short crops can help control the problem. For example, in 2020, SESVanderHave started official variety trials in the Netherlands with a variety that has very high resistance to the root-knot nematode and is also tolerant to beet cyst nematodes. Growers who include damage-sensitive crops such as potatoes, seed potatoes, carrots or salsify in their rotation will be able to use sugar beet as a 'break crop' to greatly reduce the risk of loss of quality, yield and phytosanitary certificate.
