Emergent Nematode in Sweetpotato and Other Vegetable Crops
This month Dr. Weimin Ye, nematode assay section chief at the North Carolina Department of Agriculture and Consumer Services (NCDA&CS) issued an alert warning sweetpotato growers about an emergent nematode that could threaten the crop due to the extensive damage it can cause (Figure 1).
The nematode is Meloidogyne enterolobii and causes root knot on a wide range of crops including but not limited to sweetpotato, watermelon, cucumber, pepper, tomato, potato, tobacco, soybean, and cotton. Weeds such as morning glory, pigweed, sicklepod, and marestail can also harbor the nematode. Most reports of M. enterolobii in the United States have occurred in the last five years in states such as Florida and North Carolina. The nematode has also been reported in China, Vietnam, Mexico, Brazil, Switzerland, Kenya, and Nigeria.
In North Carolina, root knot has typically been caused by Meloidogyne incognita. For several crops host resistance to M. incognita is available; however, this resistance is not effective for M. enterolobii. Thus, growers have to rely on additional control methods to reduce M. enterolobii damage to their crop. Recent nematode control trials performed by the NCSU Vegetable Pathology Lab indicate that soil fumigation before planting with the active ingredient 1,3-dichloropropene found in products such as Telone II, is effective in controlling M. enterolobii. Further testing is being conducted this growing season to identify additional fumigant and non-fumigant products available to vegetable growers for M. enterolobii control. Growers should be diligent in determining nematode levels in their fields by submitting samples to the NCDA&CS nematode lab and fumigating with 1,3-dichloropropene if the nematode threshold warrants it. Unfortunately, there is no soil test to identify M. enterolobii specifically but control measures can be applied based on overall nematode levels.
As is the case with other root knot nematodes, M. enterolobii can be spread through infested soil and infected plant material. It is critical that growers that have infested fields with M. enterolobii avoid moving soil via farming equipment to uninfested areas. Not planting pulled sweetpotato slips or infected transplants is also essential to avoid infesting your fields. Also keep in mind that planting infected material will negate any control provided by soil fumigation.
If you observe root knot nematode damage in your sweetpotato and other vegetable crops this year, we strongly suggest contacting your local extension agent and sending samples to the NCSU Plant Disease and Insect Clinic or the NCDA&CS nematode lab. M. enterolobii cannot be diagnosed visually by symptoms and differentiated from M. incognita, but there are DNA-based tests available at the NCDA&CS nematode lab to specifically confirm M. enterolobii on infected plant samples, even though this is not available for soil samples. Nematode samples submitted to the NCSU Plant Disease and Insect Clinic will be diagnosed via the NCDA&CS nematode lab. It is very important that growers determine the presence or absence of M. enterolobii in their fields through submission of infected samples to the clinic so more targeted control strategies can be recommended for the following growing season. It is also helpful to obtain information about the occurrence of M. enterolobii in particular crops or counties in the state so that we can provide guidance on how to avoid nematode spread. M. enterolobii has only been detected in fields in Columbus, Johnston, Wayne and Wilson counties but it is possible that the nematode is in other areas and has simply been undetected to date.