Homeowners have had to combat root-knot nematodes for as long as home vegetable gardens have existed. Nematodes are microscopic worms in the soil in high numbers that can cause damage to susceptible plants. Traditionally, the vegetables most affected were beans, watermelons, cucumbers, and especially three grower favorites: tomatoes, sweetpotatoes, and okra. Although there are many types of nematodes in the soil, root-knot nematodes are some of the most common and cause the large galls or knots you see on the roots of susceptible plants
Figure 1: Root-knot galls on tomato.
Photo by David Moreira
(Figure 1). These galls block the uptake of water which leads to wilting, premature death, and reduced yields. Several species of root-knot nematodes exist in South Carolina, the most common being Meloidogyne incognita. Fortunately, plant breeders have been able to develop sweetpotato and tomato varieties resistant to this root-knot nematode species. Recently, a new root-knot nematode species has been introduced into Florida, North Carolina, and South Carolina, Meloidogyne enterolobii (M.e. for short). It is unclear how this species was introduced from Asia, but it has spread rapidly in North Carolina, especially on sweetpotatoes (Figure 2) and soybeans.
Figure 2: Galling and damage on sweetpotato.
Photo by FINDMe Project
In Florida, it is common on specialty crops brought from Southeast Asia. M.e. is alarming because it can overcome the resistance that breeders have put into tomatoes and sweetpotatoes. Clemson University researchers have teamed up with plant breeders, horticulturalists, and nematologists from Florida, Georgia, and North Carolina to help commercial and home vegetable producers combat this new threat. They are surveying to determine the distribution of M.e. in South Carolina. Fortunately, that distribution up until now has been very limited. If you have planted root-knot nematode resistant varieties and are still observing galling in your roots, you may have M.e. Contact your local county agent to ask for a species identification so that, if you have M.e., a control program can be developed for you. If you want to know more about M.e, the multistate research project has a very comprehensive website at: www.findmenematode.org
