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