Grape Nematodes: Preventing Root Knot Nematodes In Grapevines

Grape Nematodes: Preventing Root Knot Nematodes In Grapevines

By: Becca Badgett, Co-author of How to Grow an EMERGENCY Garden

Occasionally, we all have a plant that is not doing its best and failing for no apparent reason. We’ve inspected the entire plant and the soil and have not seen anything unusual, no pests or bugs, no signs of disease. When we remove the plant from the ground, however, we see formidable swelling and galls among the roots. This is a classic case of the root knot nematode. This article covers what to do for root knot nematodes of grapevines.

About Grape Nematodes

It not only happens with grapevines; many plants may fall victim to grape root knot nematodes as well. These plant parasitic nematodes, microscopic in size, are possibly in the soil before planting and destructive in full orchards or gardens. Root knot nematodes of grapes feed on and cause swelling in young roots and secondary roots, creating galls.

These nematodes may be transported in soil, particularly waterlogged soil that rushes down hills with strong rainfall. Grape root knot nematode may exist in water as it moves. You never know if there are root knot nematodes of grapes, or other damaging nematodes, in the soil before you plant.

Diagnoses of soil samples at the appropriate laboratory is the only way to know for sure. Reports from previous crops grown in the field or orchard may provide information. However, aboveground signs from nematodes are not conclusive. Symptoms such as reduced growth and vigor, weak limbs, and reduced fruiting may be the result of root knot nematodes but can be caused by other issues. Root knot nematodes of grapes display irregular damage patterns.

Root Knot Nematode Control

Root knot nematode control is often a complicated, lengthy process. Letting the ground lay fallow helps decrease the nematode population, as does planting cover crops that don’t feed the organisms, but these practices do not prevent re-infestation.

Fumigation of the soil is sometimes helpful. Soil amendments such as compost or manure help produce a better crop. Likewise, proper irrigation and fertilization help vines resist damage. Keeping your grapevines healthy makes them better able to withstand the effects of grape nematodes.

Beneficial nematodes may help but don’t fully get rid of them. There is no known way of preventing root knot nematodes. According to the University of Florida, the following practices can help avoid some of the damage:

  • Buy resistant seeds, marked with an “N”
  • Avoid moving infected soil, by hand or with farm tools
  • Rotate crops and plant with those known to reduce nematode populations, such as broccoli and cauliflower
  • Solarize the soil
  • Amend the soil with nutritious materials, such as shellfish fertilizer

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Nematodes in Turf

Nematode damage manifests itself in both above and below ground symptoms. Above ground symptoms typically include thinning, wilting or death of turfgrass. These symptoms usually occur in irregularly shaped patches that will spread outwards slowly over time if left untreated. Root-knot nematode symptoms often emulate several fungal diseases and can cause chlorotic patches in turfgrass stands.

Below ground symptoms on turfgrasses include short, stubby root systems. Dark lesions on roots are characteristic of nematode feeding damage, particularly near the root tips. Damage typically occurs at the root tips resulting in a blunted root system and the absence of feeder roots. Root-knot nematodes cause galling on turf similar to other crops, although the galls are smaller and can be difficult to identify properly without the aid of magnification, i.e. hand lens, dissecting microscope, etc.

Grape Root Knot Nematode - Tips For Root Knot Nematode Control In Grapes - garden

The University of California, Davis, and Global Plant Genetics, a European company that manages intellectual property for various crops, have entered into an agreement to commercialize and distribute two UC Davis-patented grape rootstocks in Europe. Both rootstocks, GRN1 and GRN3, are resistant to a number of nematodes, including root-knot, which are microscopic, unsegmented roundworms that feed on, and harm, the roots of grapevines.

Rupert Hargreaves, co-owner of Global Plant Genetics

Nematodes cause damage to plants by stunting root elongation, changing root growth patterns and removing nutrients. And since many countries around the world prohibit the use of soil sterilants to control them, the economic impact of damage from nematodes is growing.

Efforts to find nematode-resistant grape rootstocks began at UC Davis in 1993, when 75 crosses were made, producing 5,000 individual seedlings for assessment. Evaluation of the results of these crosses began in 1996, with 1,000 seedlings identified — from which the best 100 were advanced to test for nematode resistance. This work was undertaken by Andy Walker, grape breeder and professor in the Department of Viticulture and Enology, and Howard Ferris, professor in the Department of Entomology and Nematology, both from UC Davis.

Walker and Ferris continued their testing and laboratory analysis, using soils with high known and quantifiable nematode infestations as well as plants in pots infected with nematodes. Tests were also undertaken, against a control variety, at temperatures of 30 degrees and higher, where root-knot nematode resistance often breaks down. Having narrowed down the group of seedlings to five selections, two were identified by UC Davis for commercialization in Europe — GRN1 and GRN3.

GRN1 was found to be the most nematode resistant of all the rootstocks tested. It offers resistance to root-knot, dagger, citrus, lesion and ring nematodes as well as phylloxera, a tiny aphidlike insect. This rootstock may be particularly beneficial to wine producers in areas where soil sterilization is no longer an option. GRN1 has a relatively deep rooting profile with moderate vigor and will likely suit warmer climates. It is potentially adaptable to all grape cultivars and has proven easy to graft assuming well matured cuttings are selected.

GRN3 has moderate to high vigor and is more likely to do well in lime-based soils. GRN3 is easy to graft and more adaptable to colder climates. It offers resistance to root-knot, dagger, citrus, lesion and phylloxera, but not ring nematodes.

“We are pleased to be working with Global Plant Genetics as our licensee in the EU to commercialize these rootstock varieties,” said Dushyant Pathak, associate vice chancellor of research and executive director of Venture Catalyst at UC Davis. “The novel properties of the rootstocks developed by professors Walker and Ferris are expected to support the environmentally and economically sustainable production of grapes within the European context.”

What do nematodes do to fruit crops?

Plant-parasitic nematodes (Figure 1) are microscopic worm-like animals that live in soil or plant tissues. They acquire nutrients from plant tissues by perforating the tissue cells with a hollow, needle-like feeding structure called a stylet or spear (Figure 2). Different kinds of nematodes can be classified into one of three groups depending on how and where they feed on the plants:

Diagram of a generic plant-parasitic nematode.

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Diagram of a plant-parasitic nematode stylet.

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Ectoparasitic nematodes are those that always remain outside the plant root tissues (Figure 3), feeding on surface cells or those within reach of their probing stylets (spears) from outside. The most common symptoms of damage from these nematodes are stunted or stubby root systems (Figure 4). A few kinds of ectoparasitic nematodes can transmit important plant viruses to the tissues on which they feed.

Ectoparasitic nematodes from a soil sample.

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Abbreviated “stubby” roots caused by ectoparasitic nematodes.

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Migratory endoparasitic nematodes move through root tissues, feeding on and killing relatively tender cells as they go (Figure 5). They weaken roots by physical damage to tender tissues, and their tunnels can dramatically reduce roots’ resistance to invasion by fungi and bacteria. Common symptoms caused by these types of nematodes are dark, sunken lesions on roots and rotting of roots (Figure 6).

Migratory endoparasitic nematodes (stained red) tunneling within a root.

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Rotting roots caused by migratory endoparasitic nematode.

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Sedentary endoparasitic nematodes penetrate young roots at or near the growing tip and establish permanent feeding sites there. After this they no longer need to move, so they swell as they mature (Figure 7). They steal nutrients, disrupt water and mineral transport, and also provide excellent sites for other pathogens and pests to invade the root. Affected roots may have galls or may simply appear to be poorly developed.

Development of sedentary endoparasitic root-knot nematodes within roots. A. Second-stage juveniles enter root, cause a feeding site, and then no longer move. B. Juveniles swell and molt several times. C. Adult female nematode is swollen and starting to lay eggs. D. Root tissue pulled back to show adult female nematode.

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Organically Acceptable Methods

Sanitation, cultural controls, crop rotation are acceptable methods.

Cultural Practices

Plow under infested plants after harvest to prevent further reproduction of nematodes. Reduce stress on plants by proper fertilization and irrigation. In areas with hot summers, soil solarization can provide partial control of root knot nematode when combined with composted chicken manure it may provide more complete control. Solarization can also reduce populations of soilborne fungi pathogens and weed seed.

Crop Rotation

Crop rotation is not very effective against root knot nematodes due to their wide host range. Strawberries may be a suitable rotation crop in fields in which the species of root knot nematode has been identified. They are nonhosts to M. incognita and most populations of M. javanica, but allow reproduction of M. hapla. Rotation will not be effective against needle nematodes in the Imperial Valley, because their host range includes most crops grown in the Valley.


Thoroughly clean soil from all equipment with water to prevent the spread of infestation. Do not allow irrigation water to flow from an infested field to other fields without impounding. Prevent animal grazing and movement from infested to uninfested fields.

Chemical Control

Damage thresholds have not been developed for nematodes on lettuce. Treatment for root knot nematode is advised if any are detected in sandy, loamy sand, or sandy loam soils, or where high numbers are found on any soil type, especially in spring and summer plantings. Consider treating for needle nematode before lettuce is planted in the Imperial Valley whenever this pest is present in soil samples, especially for fall planting when high soil temperatures favor nematode activity. Contact your farm advisor for advice on specific situations.

Common name Amount per acre REI‡ PHI‡
(Example trade name) (hours) (days)
Pesticide precautions Protect water Calculate VOCs Protect bees
Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.
(InLine) Label rates see label NA
COMMENTS: Multi purpose liquid fumigant for the preplant treatment of soil against plant-parasitic nematodes, symphylans and certain soil-borne pathogens (e.g. Fusarium and Verticillium) using drip irrigation systems only. Use of a tarp seal is mandatory for all applications of this product. Fumigants such as 1, 3-dichloropropene are a prime source of volatile organic compounds (VOCs), which are a major air quality issue.
(Telone EC) Label rates see label NA
COMMENTS: Liquid fumigant for the preplant treatment of soil against plant-parasitic nematodes and certain other soil pests in cropland using drip irrigation systems only. Fumigants such as 1, 3-dichloropropene are a prime source of volatile organic compounds (VOCs), which are a major air quality issue.
(Telone II) See comments see label NA
COMMENTS: The application rate for Telone II cannot exceed 33.7 gal/acre. In dry soils with slight surface moisture, the overall value of a Telone II application is equivalent to that of methyl bromide. Fumigants such as 1,3-dichloropropene are a source of volatile organic compounds (VOCs) but are minimally reactive with other air contaminants that form ozone. Become familiar with procedures that minimize off-gassing of fumigants.
D. METAM SODIUM* 50–75 gal see label NA
COMMENTS: A soil fumigant. Beds must be free of large clods and moistened by rainfall or irrigation before application. Soil temperatures should be between 50° and 90°F at a 3–inch depth. Broadcast rate is 50–75 gal/acre, but band applications may be made on the bed to lessen the overall application rate. Also used as a bladed application to high-density plantings of baby lettuce plantings on 80-inch wide beds. The label requires a 14–day preplant interval between application and planting. Avoid moving untreated soil into the banded area. Fumigants such as metam sodium are a prime source of volatile organic compounds (VOCs), which are a major air quality issue.
. or .
METAM POTASSIUM 30–60 gal see label NA

UC IPM Pest Management Guidelines: Lettuce
UC ANR Publication 3450

Watch the video: How nematodes damage plants.