Nematodes in Sweet Potatoes

Charles Overstreet  |  3/22/2005 1:48:42 AM

Roots don't size up properly.

Blisters formed on roots by root-knot nematode.

Females of root-knot nematode beneath a blister.

Nematodes are a serious pest to both our sweet potato industry and for those people growing them in a home garden. These pests affect the total production and quality of the sweet potato. Since the damage occurs to roots below ground, they are often not recognized as being a problem.

Two nematode species cause most of our damage. Root-knot nematode has been recognized for years as one of the most important nematodes that injure sweet potatoes. It is very widespread in Louisiana and attacks a wide range of plants. Reniform nematode is the other nematode that can cause problems on sweet potatoes. This nematode has very recently become widespread. Cotton appears to be the primary crop that reniform nematode has spread on throughout the state. Unfortunately, reniform nematode does extremely well on sweet potatoes.

Plant-parasitic nematodes can damage plants in several ways. Root-knot nematode can cause roots to be malformed or cracked or to appear roughened. Aboveground symptoms are a general stunting or yellowing of the plant. These plants look like they are lacking in fertility. If this nematode attacks early in the growing season, small galls can be seen where it has attacked the root system. This pest can also enter into the enlarging roots later in the growing season. Root-knot females can often be found in corky areas within these roots. The females are white or yellowish, often occurring in discolored areas within the root. Although they are quite small, they can just be seen without the aid of a magnifying glass.

Reniform nematode has recently begun showing up as a more-serious pest than root-knot nematode and is a serious threat to this crop. This pest causes the root system to be poorly developed, be discolored and lack feeder roots. Cracked roots are also associated with this nematode, which leads to quality problems.

There are several methods used to reduce losses by nematodes. The variety Bienville has been selected for resistance against the root-knot nematode. The variety Beauregard is the dominant variety now in Louisiana but is susceptible to both root-knot and reniform nematodes. Commercial growers will need to treat fields before planting with either a preplant fumigant such as Telone II or preplant nematicide such as Mocap 10G or EC. Temik 15%G can be applied at the time of planting. Home gardeners need to plant behind crops that are not good hosts for the root-knot nematode or have resistance against it such as found in many tomato varieties or Mississippi Silver cowpea.

Nematodes can cause serious losses to sweet potatoes. Don’t let them be a surprise to you at harvest

Nematodes in sweet potato
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