Cause Meloidogyne hapla (northern root-knot nematode) is a sedentary endoparasite of which only second-stage juveniles (the infective stage) and adult males (which may be rare) are in soil. Juveniles move in the water film on soil particles and invade the root tip. They move through the root and locate a parenchyma cell in the root cortex. The feeding modifies the cell to form a large specialize feeding cell called a giant cell. The nematode stays in this location through two more molts to become a female adult. Males form under stress conditions. Females lay eggs in a gelatinous matrix outside of or just inside of the root. Spread to new areas usually is due to planting infected, rooted plants or moving infested soil.
Root-knot nematode was found in 10% and 66% of Oregon and Washington vineyards surveyed, respectively. In eastern Washington, root-knot nematodes may be more problematic in vineyard planted on site previously cropped to potato or alfalfa.
Symptoms Small distinct galls on roots; poor growth; shortened lifespan of the vine; low vigor; reduced yield. May also develop premature leaf senescence. Affected plants are generally concentrated in circular or oval-shaped areas in the field. Young plants may be stunted or even die due to infection. Other problems, such as Armillaria root rot or phylloxera, can cause a similar damage pattern.
Sampling Take soil samples well before planting to implement management procedures. It may be several weeks before crops can be planted after soil fumigation. Fall sampling, when populations are highest, for crops to be planted the following spring is an excellent strategy.
Take samples 1 ft from the vine and in the vine row. Remove the top 2 to 3 inches of soil and sample 1-ft deep with a 1-inch-diameter soil tube. Take 10 to 20 subsamples in a given area and combine into one sample. Include roots as well as soil. Yield loss in eastern Washington has been associated with population densities around 200 to 300 juvenile nematodes per 250 cc soil.
- Use clean rootstock.
- Preplant Anaerobic Soil Disinfestation may be helpful even in the PNW. First rice bran is incorporated into the soil followed by irrigated to near field capacity. Then place clear oxygen impermeable plastic (such as anti-condensation film) on the prepared ground. This summer treatment needs to reach soil temperatures of 90F. Use in combination with other techniques.
Chemical control The key in managing nematodes on perennial crops such as grape is to protect new roots from nematode feeding. This allows roots to establish to the point they can tolerate nematode feeding after the chemical's effects dissipate.
- Preplant fumigation. Check labels for buffer zone requirements.
- 1,3-dichloropropene which is available in various formulations including: Telone II (97% 1,3-D), C-17 (17:81% chloropicrin:1,3-D), and C-35 (35:63% chloropicrin:1,3-D). Soil conditions where grapes are grown are often not conducive for optimum performance of this fumigant in the PNW. Check label for rates and proper ground preparation before application. 5-day reentry. Restricted-use Pesticide.
- Dominus at 10 to 40 gal/A. Apply as a shank injection to an entire field or raised beds when soil temperatures are above 60°F but not greater than 90°F. 5-day reentry.
- Metam sodium-generating products such as Basamid G or Vapam HL. Rates will depend on soil type. Converting the active ingredient into the gaseous phase depends primarily on soil moisture and temperature; follow the label carefully. In the PNW, if application is made in the spring wait up to 21 days before planting to avoid phytotoxicity. 5-day reentry. Restricted-use pesticide.
Postplant chemical use.
- Ecozin Plus at 25 to 56 oz/A through a drip irrigation system. Label suggests using additives to aid penetration into the soil and to make applications in the morning. Efficacy in the Pacific Northwest is unknown. 4-hr reentry. O
- Nema-Q at 1.5 to 3 gal/A for the first application followed by 5 to 10 regular applications at 2 quarts/A. Efficacy in the Pacific Northwest is unknown. 24-hr reentry. O
- MeloCon WG (Paecilomyces lilacinus strain 251) at 2 to 4 lb/A plus a soil wetting agent can be applied to established plants, although it might be better used when applied to plants just before planting. Stable for only days at room temperature, weeks in the refrigerator or for a year if frozen. Unknown efficacy in the PNW. 4-hr reentry. O
Note: Some registered products offer only suppression of this disease and thus are not recommended for use. These products include Movento.
Reference East, K.E., Zasada, I.A., Schreiner, R.P., and Moyer, M.M. 2019. Developmental Dynamics of Meloidogyne hapla in Washington Wine Grapes. Plant disease, 103:966-971.