(07/26/18) BATON ROUGE, La. — The LSU AgCenter is in the vanguard of an attempt to contain and eradicate a significant plant pest that has been identified in Morehouse Parish.

The guava root-knot nematode showed up in a shipment of plant material from North Carolina, said AgCenter nematologist Charlie Overstreet.

Nematodes are microscopic worms, and the largest adult females are smaller than the head of a pin. They feed on plant roots, creating large galls that sap the strength from the plant. Although they are a problem in many crops, including soybeans and cotton, they’re particularly bad in sweet potatoes because the crop is the root itself.

Overstreet is undertaking an intensive survey of Louisiana fields to monitor the presence of the guava root-knot nematode. So far, he has not found any.

The AgCenter operates a Nematode Advisory Service to correctly identify nematode problems and recommend the best methods of managing these pests. The Louisiana Department of Agriculture and Forestry submits about 100 horticulture samples each year, Overstreet said.

“We look for all types and will particularly be looking for this nematode,” he said. “Most samples from potted plants are clean and have no nematodes.”

The devastating pest is similar to the Southern root-knot nematode that’s prevalent in Louisiana, but this species can cause significantly more damage to infested crops.

Guava root-knot nematodes are more prolific and produce larger galls. “A sweet potato could have hundreds of egg masses, each with 500 eggs,” Overstreet said.

It’s considered the most destructive nematode in the world. “We don’t think it’s widespread in Louisiana. It’s only in one field, and we’re trying to eradicate it,” he said.

The grower recognized the damage in seed material, but by then it had been planted in a few acres in a single field.

“We’re taking extreme measures in the infested field,” Overstreet said. Any equipment that enters the field is thoroughly washed, and workers’ boots are disinfected whenever they leave.

Because the nematodes can only be moved by moving the soil or plant material they’re living in, the current population can be isolated and controlled.

“We do have a plan in effect,” Overstreet said. The field where the seed material was planted is now under plastic sheets to capture heat from the sun and sterilize the soil. Later, the area will be fumigated to further control the pests. Finally, the field will be left fallow with nothing growing in it.

The field later will be planted in crops such as corn, grain sorghum or other crops that are resistant to guava nematodes.

“We want to eventually eliminate the food source and starve them to death,” Overstreet said. “We will be monitoring surrounding fields and other locations in the state this fall to see if any other areas might have this nematode. At this point we are concerned but not worried yet.”

Large knots and bumps on a sweet potato are an indication of an infestation by guava root-knot nematodes. Photo by Charlie Overstreet/LSU AgCenter

Egg masses and females of the guava root-knot nematode are apparent in a cross section of a sweet potato. Photo by Charlie Overstreet/LSU AgCenter

A tomato root is severely galled by the guava root-knot nematode. Photo courtesy of Don Dixon in Florida