Stephen Jordan, University of Wisconsin-Madison
Nematodes are wormlike non-segmented invertebrate animals found in marine, freshwater, and terrestrial habitats. Plant-parasitic nematodes have a cell piercing feeding apparatus called a stylet, which is used to extract nutrients from the plant cell. Plant parasitic nematodes feed on roots, reducing vigor and yield of the vine usually in irregular patterns across the vineyard. Damage patterns are frequently associated with soil textural differences. Nematodes create openings in roots through which other microorganisms can enter, and some species are able to transmit viruses from one vine to another. All these factors increase the susceptibility of plants to environmental stress, including drought stress and winter injury. Nematodes are transmitted by anything that can move soil, including machinery, wind, and water. There are six main groups of plant parasitic nematodes that cause damage to grapevines; dagger, root knot, citrus, lesion, ring, and stubby root nematodes.
Dagger nematodes feed on the roots, often resulting in swollen root tips and preventing the roots from functioning properly, reducing vigor and yield. Roots often die as a result of this feeding. The greater danger of dagger nematodes to grapevines is through transmission of viruses such as grape fanleaf virus, tobacco and tomato ringspot virus, and peach rosette mosaic virus.
Root knot nematodes penetrate grapevine roots and induce swelling, causing the formation of galls. Galls disrupt the uptake of nutrients and water, decreasing vigor and yield. Affected vines are generally in circular or oval-shaped areas in the field.
Citrus nematodes establish feeding sites with their heads embedded inside the roots and their posterior ends outside the roots. Citrus nematodes produce a gelatinous matrix around the roots, causing soil to cling to the roots, giving them a “dirty” appearance when removed from the soil. Their feeding disrupts the uptake of nutrients and water, and interferes with plant growth, causing slow decline, loss of feeder roots, poor vine vigor and loss of yield.
Lesion nematodes feed on roots either from outside the root or by entering along the root and moving between cells. High population levels in newer plantings can cause the formation of brown root lesions and restricted root growth.
Ring nematodes feed on the tips and sides of roots and reduce vine vigor and yield.
Stubby root nematodes are more common in sandy soils. Feeding of stubby root nematodes reduce vigor and yield in heavily infested vines.
Pre-plant nematicidal fumigants and postplant nematicides are available for control of nematodes. These products are under increasing regulation, therefore, availability might be limited. Make sure to read labels before choosing a product to ensure that it is allowed in your state and that application method and rates follow the label recommendations.
Reviewed by Damon Smith, Oklahoma State University and Kevin Ker, Brock University