Guava Root-Knot Nematode: 2024 Emergency Management Recommendations for Sweetpotato Producers

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Nothing beats the delicious and nutritious sweetpotatoes from North Carolina. Yet the guava root-knot nematode (GRKN; Meloidogyne enterolobii) continues to threaten production of this important vegetable in North Carolina. To keep fields productive, it is critical that all sweetpotato producers monitor for damage from this nematode in their fields and take avoidance actions to keep the nematode from establishing in new fields. Below are recommendations for sweetpotato growers and seed producers.

Composite photograph of guava root-knot nematode damage on sweetpotato. On the left side are two photos of storage roots with galls caused by GRKN. On in the middle is GRKN galls on a sweetpotato fibrous root. On the right is a sweetpotato with skin peeled to reveal small brown flecks, which are evidence of female GRKN feeding just below the sweetpotato skin.

The guava root-knot nematode (GRKN, Meloidogyne enterolobii) causes galls and bumps to form on the storage and fibrous roots of sweetpotato. Small brown- to black-colored flecks may be seen if the skin is peeled away. These flecks are the bodies of the female nematodes embedded in the sweetpotato.

Spring and Summer GRKN Recommendations for Sweetpotato Producers

  • “Start Clean, Stay Clean” – if purchasing seed, buy certified seed. Visually inspect roots and do not plant roots that have galling symptoms.
  • Fumigate with Telone II (1,3-dichloropropene) at a rate of 7-8 gal/Ac in the bed. Soil temperature must be greater than 40°F at application depth (check product label for additional information about optimal soil conditions). It is also optimal to time fumigation with a light rain following application to seal product into the soil.
  • Pre-plant incorporate treatment with full rate of Salibro (fluazaindolizine) or use full rate of Velum Prime (fluopyram) in a transplant water application. Note that any sweetpotatoes treated with Salibro must stay in a domestic market.
  • Manage weeds, especially between the rows.
  • Soil sample fields yearly for nematode analysis. It is recommended to sample after harvest, but prior to cold temperatures, which may freeze the ground. However, a soil sample can be collected anytime of year when a nematode issue is suspected. To determine if GRKN is present, request a molecular test by checking the appropriate box at the top left of the sample submission form.
  • Rotate fields with known GRKN issues to non-host crops such as peanut, corn, sorghum sudangrass, or sunn hemp.
  • Sanitation recommendations for stopping the spread of GRKN:
    • As a nematologist, I am a fan of rubber boots – tuck pant leg into boot, and thoroughly scrub off soil from boots between fields.
    • Wash soil off from tractors, setters, and trucks between fields.
    • Recommended to use a 10% bleach (chlorine) solution for disinfecting. However, even using a garden hose and plain water to wash off soil will reduce the risk of spreading GRKN.
    • If purchasing used equipment, or renting or borrowing equipment, wash off all soil before it arrives at your farm. This is recommended regardless of the county or state from which the equipment is originating from.

Spring and Summer GRKN Recommendations for Sweetpotato Seed Producers

In addition to the above sanitation and management recommendations, the following are specifically provided for seed producers:

  • Seed roots – cull out any with visible galling symptoms (please see photo). Dispose of these galled roots in an area where they won’t impact another crop. Infected roots may also be sent to a processor or canner.
  • Slips – cut plants above the soil line. Do not pull plants such that roots are brought up out of the soil. Don’t lay cut slips directly on soil, rather place immediately into crates and keep crates off the ground. Shake, brush, wash off with plain water any soil stuck to cut slips. GRKN cannot infect the green stems or leaves of the slips. Clean knives with a 10% bleach solution at each breaktime, or more frequently, if possible.

It is important to note that GRKN is not only a management issue in sweetpotato, but also a broad range of other crops frequently grown in rotation with sweetpotatoes here in North Carolina. GRKN can feed on and cause damage in tobacco, soybean, cotton, fruiting and leafy vegetables, and some broad-leaf cover crops. Following sanitation measures and chemical management recommendations in these other crops will aid in managing GRKN across years and crops. Unfortunately, there are no commercial sweetpotato, soybean, cotton, tobacco, or vegetable varieties genetically resistant to GRKN at this time.

If you think you may have GRKN, and need assistance with diagnostics or management, please contact your local Extension agent. Soil samples can be sent to the NCDA&CS Nematode Assay Lab. For additional nematode management options in sweetpotato and other crops, please refer to our nematode disease factsheets.