Guava-RKNematode-Damage-Sweet-Potato-LSU LSU AgCenter
Egg masses and resulting damage from guava root-knot nematodes are clearly visible inside this dissected sweet potato.

LSU AgCenter addressing guava root-knot nematode concern

A new species of root-knot nematode has been confirmed in northeast Louisiana and researchers are acting to stop it from spreading to other parts of the state.

The presence of the root-knot nematode, Meloidogyne enterolobii (M. enterolobii) (also called the guava RKN) was recently confirmed at a Morehouse Parish farming operation in northeast Louisiana. This soil-borne microscopic, plant-parasitic pest has a high rate of reproduction and a wide host-plant range that includes soybeans, sugarcane, cotton, and sweet potatoes.

The LSU AgCenter will begin a statewide nematode survey this fall to determine if farmers in other parishes across the state are finding any evidence of this invasive pest. “We will also start visiting sweet potato operations across our state, looking primarily at the storage roots of the sweet potatoes for visible evidence,” explains Dr. Charles Overstreet, nematologist, Plant Pathology and Crop Physiology Department, LSU AgCenter. “It’s very similar to the southern RKN.”

The guava RKN is more aggressive and causes more plant damage. One distinct feature of its presence will be when damage to a southern root-knot nematode-resistant plant variety occurs. “If a grower chooses a variety with resistance to the southern RKN and those plants show galling of the roots or plants become stunted, you can pretty much count on it being this new species of guava RKN,” adds Overstreet.

Soils and Testing

The guava RKN was first identified on Florida ornamental nursery stock in 2001. By 2011, it was found in North Carolina.

The Louisiana Department of Agriculture and Forestry is currently working with the producer on whose farm the guava RKN was initially found to monitor the situation and hopefully reduce the spread of the guava RKN.

“Nematodes are often spread through the transportation of farm equipment,” explains Mike Strain, D.V.M. and Commissioner of the LDAF. “Cleaning soil off equipment, tires, and footwear before going to another field is one of the best ways to reduce the spread of nematodes.”

Symptoms of both nematodes species are similar. The only way to positively differentiate southern RKN damage from guava RKN damage is through molecular testing and analysis. In general, all nematodes are found more in lighter, sandier soils than in heavier or clay soils. “We will be requesting soil samples or plant roots showing galling from survey participants,” adds Overstreet

A PDF-formatted survey form is available at: http://www.lsuagcenter.com/nas. Once completed surveys and soil samples have been received in the laboratory, infested soils will be place on a tomato in an LSU AgCenter greenhouse and grown for at least 30 to 45 days to get galling and mature females. If nematodes are present, the mature females will be processed in the laboratory for specific species identification. Results from soil samples should be available in approximately two to three months.

“We would really prefer to have plant roots affected with galls because we can take those galls and extract the female nematodes from the fibrous gall tissue,” explains Overstreet. “We can then place the female nematodes in test tubes where their contents can be analyzed more quickly than if we had to grow them on a tomato host plant.”

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