Source: NCDA&CS, 11/8/19

North Carolina is one of only a few states that offer growers a nematode molecular diagnostic service. Starting Nov. 1, the Agronomic Services Division’s fee for nematode species identification through molecular diagnosis will be $23 per sample. Fees collected go towards laboratory supplies and technical staff needed to process these samples.

All molecular diagnostic samples are considered a high priority, and are processed immediately upon being received, even during the peak laboratory season.

Molecular diagnosis is the only reliable way to identify the most damaging root knot nematodes to the species level, and interest in that level of identification is on the rise because of concern over the Guava root knot nematode (Meloidogyne enterolobii), which is a highly damaging pest of sweet potatoes, said Dr. Weimin Ye, section chief of the Agronomic Services Division’s Nematode Lab.

“Since July 1 of this year, our nematode lab has performed more than 600 molecular diagnostic identifications,” Ye said. “That is more than double the requests for the same time period last year.”

Since molecular diagnosis is time consuming and expensive, growers should give careful consideration before requesting this test.

The decision to request molecular diagnosis must be made upfront since the fee is charged upon receipt of the samples. Because of the high volume of samples handled by the Nematode Assay Lab, soil samples can’t be held pending the results of a predictive assay.   

The Agronomic Division recommends that growers only submit three to five molecular diagnostic samples per farm. Each sample should represent a different field on the farm. A good sample will come from a mixture of multiple soil cores collected randomly across a field or known hot spots.

When available, root galls or galled sweet potato are the preferred materials.  Female nematodes can be dissected from this plant material to obtain the nematode’s DNA (genetic material).  In comparison, soil samples contain only juvenile root knot nematodes which are much smaller making them more difficult to obtain DNA.

Molecular diagnostic samples should be sent to the lab in shipping container marked clearly on the outside as “Molecular Diagnosis” to ensure expedited service. Molecular diagnostic samples should never be put on the same sample information form or placed in the same shipping container as routine predictive or diagnostic samples.

Growers should continue routine monitoring of nematodes in all their fields by submitting predictive samples in late summer or early fall.  If a high population of root knot nematodes is discovered in one or more predictive samples, then the grower should consider resampling that field and requesting molecular diagnosis.

To save labor and time, the grower may want to collect molecular diagnostic samples (three to five samples per farm) at the same time that predictive sampling is done, but keep in mind, the molecular diagnostic samples need to be shipped separately to the lab.

The N.C. Department of Agriculture and Consumer Services Agronomic Services Division provides diagnostic and advisory services that increase agricultural productivity, promote responsible land management and safeguard environmental quality.