Helpful Tips for Handling Root-Knot Nematodes in Tomatoes
A juvenile root-knot nematode burrowing into a tomato root.
Photo courtesy of USDA-ARS
Tomato growers have reported cases of root-knot nematode resistance breakdowns over the past few years. Dr. Jaspreet Sidhu, Vegetable Crops Advisor, University of California Cooperative Extension, who works closely with processing tomato operations and has seen some resistance issues up close.
How can growers recognize a problem?
Nematode populations are widespread throughout warm regions in Central and Southern California, especially in light-texture soils. Nematode-infested plants appear stunted and less vigorous with severe galling of roots. For the above-ground symptoms, growers and PCAs should watch for poor growth and crop wilting (hot weather) due to limited water availability caused by a disrupted root system. Infected plants also respond poorly to fertilizer. Damage usually appears as irregular patches in the field.
What actions do you recommend if growers suspect root-knot nematodes breaking through?
Screen Pre-Planting. It is crucial to assess the population levels in the soil prior to planting based on soil sampling and field history.
Treatment Strategy. There are certain products registered for pre-plant use. However, for in-season damage, you can apply Vydate (Oxamyl, Corteva), and it can be applied through drip irrigation lines. Repeated applications are needed for continued protection during the growing season.
Pick the Right Varieties. You should check the variety planted to make sure of its source and resistance.
Continue Sampling. Also, it is advised to take soil samples and get the root knot nematode species identified.
Why does resistance break down?
The resistance to root-knot nematodes on processing tomato varieties is monogenic, conferred by a single dominant gene — Mi. Continuous cultivation of resistant varieties and over reliance on resistance could lead to development of resistance-breaking nematode populations.
There are also some studies that suggest resistance breakdown at high soil temperatures (greater than or equal to 32ºC or 90ºF). Also, some other studies have suggested that the gene regains its function once the soil temperature lowers. The Mi gene also has target specificity, which means it is effective against three root knot nematode species: M. incognita, M. javanica, and M. arenaria. It does not impart resistance against M. hapla, which is also found in some tomato production areas.
If growers find breakthroughs, what do you recommend they do?
It is imperative to report the issues to confirm the resistance breakdown, as it will provide an opportunity for researchers to investigate the issue and address the problem.
You should contact your local farm advisors or, if you are growing processing tomatoes in California, the University of California Cooperative Extension office. You can contact the specialist on the UC Riverside or Davis campuses.
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