About Root-Knot Nematodes
Root-knot nematodes are plant-parasitic round worms of the genus Meloidogyne. This is one of the few types of nematodes that are parasitic, meaning they require a plant host to survive. These nematodes are parthenogenic, meaning that a female can reproduce without the need of a male. New generations of root-knot nematodes can occur every 28 days, as long as the proper conditions are available. A female root-knot nematode will lay 300-500 eggs in the gall of the plant. Newborn nematodes hatch from the eggs and penetrate the center of the root. These nematodes are capable of overwintering in harsh conditions. After overwintering, new adults develop from the larvae, repeating this cycle.
Root-Knot Nematodes Identification and Habitat
The name “Root-knot Nematode” is derived from the knot-like swellings they cause in the roots of the plants they inhabit. This is usually an easy way to identify an infected plant, except for smaller plants whose roots aren’t as visible as larger plants. Infections also cause growth stunts, chlorosis, and wilting due to the feeding on roots. The host plant will be in visible decline and may eventually die as a result of the infection. Root-knot nematodes are microscopic, so they are difficult to see with the naked eye.
Root-knot nematodes favor warm weather with high humidity and sandy soil. This species develops fastest in moist soil with temperatures above 80°F, growing from egg to adult in roughly 25 days. Most nematodes can be found a few inches below the soil, but they are capable of following roots several feet down. Although they prefer warm weather, these nematodes are able to survive harsh winters below the soil.
Root-Knot Nematodes Management and Control Methods
Most of the cultural controls for root-knot nematodes require careful planning and management. First, cover crops are useful when trying to lower nematode populations. For example, marigolds produce chemicals that are toxic to nematodes, but also help stabilize topsoil and nourish the soil. Crop rotation is a viable option if an alternative non-susceptible crop with high economic return is available, but sometimes this can be a tedious procedure. Solarization and flooding are proven to be effective at diminishing nematode populations in soil, but only if the climate is warm enough and if a field can be denied cultivation throughout the treatment.
Pre-plant soil fumigants can be effective in preventing root-knot nematodes. A few examples include dazoment and methyl bromide. For these to be effective, a cover must be put over the soil to keep the fumigant in the soil long enough. Unfortunately some fumigant are currently being phased out, so be aware of this while planning. Additionally, nervous system toxins can be effective in controlling nematode populations, but beware of the dangers to humans that these can cause. Be sure to read labels for cautionary advice and application guidelines.