Nematodes are microscopic soil-inhabiting roundworms that attack root systems. These pests feed on the roots, causing them to gall or swell, which interferes with the normal uptake of nutrients and water. Root knot nematodes, root lesion nematodes and citrus nematodes are the most common fig tree pests. Nematodes often are hard to control because they easily spread via running water and gardening tools.
Inspect your fig tree's roots for nematodes. Dig into the soil and uncover the roots. Check the roots for galls or swelling that look similar to air bubbles. Nematodes live and feed within these galls, which can grow as big as 1 inch in diameter.
Examine your fig tree's leaves and fruit for symptoms of nematodes. Above-ground signs of a nematode infestation include wilting foliage, yellowing leaves, smaller fruits and fewer leaves.
Collect a soil sample for testing. Take a small soil sample from around the roots of the affected fig tree. Lightly moisten the soil and place it in a clean plastic bag or plastic container. Labs are not able to test dry soil samples. Refrigerate the soil sample until you take it by your local garden center or university for positive nematode identification.
Complete soil solarization around your fig tree. Break up any dirt clods and remove all rocks and sticks. Moisten the soil and cover it with a plastic tarp. Secure the edges with bricks or rocks. Leave the tarp in place for four to six weeks during the summer. Nematodes and their eggs die when the soil temperatures get higher than 125 degrees Fahrenheit. This soil solarization process temporarily reduces the nematode populations in the top 12 inches of upper soil.
Add amendments to the soil around your fig tree. Compost, peat and manure help to control nematode populations by increasing the nutrient- and water-holding capacity of the soil. Healthier trees have a reduced risk of nematode infestation. Some soil amendments also release toxins that can kill nematodes.