What's Attacking my Tomatoes?
Root-knot, sting and stubby-root nematodes are the three major species of nematodes present throughout the tomato-producing states. Various diseases – which gain access to tomatoes through entry ways created by nematodes – also can result in significant damage.
Root-knot nematodes provide openings for Fusarium wilt.
D. Langston, UGA, Bugwood
- Root-knot nematodes are named for the galls created on plant roots by the nematode. These nematodes are some of the most dangerous nematodes and can be found in nearly any field, but are most commonly found in sandy soils. The density of root-knot nematodes is typically scattered within an infested field.
The occurrence and severity of Fusarium wilt and Verticillium wilt are increased significantly in fields with root-knot nematodes. Infected plants can be easily identified by digging up stunted plants and checking for swollen knots on the roots.
Potential host weeds: prickly sida, smallflower morningglory, ivyleaf morningglory, bermudagrass, johnsongrass, cocklebur, goosegrass, red-root pigweed, purple nutgrass, yellow nutsedge, purple nutsedge, smartweed, teaweed, lambsquarters, groundcherry, crotalaria, sicklepod
- Sting nematodes result in reduced root and plant growth, and the root tip often swells, causing the root to appear to be cut off. Sting nematodes prefer sandy soils and are commonly found along the Atlantic and Gulf coasts. They cause the most damage to young plants with developing root systems, remaining in the soil and feeding on root tips. Sting nematodes generally need at least 80 percent sand content in soils to survive. Heavy infestations of sting nematodes can cause total crop destruction.
Potential host weeds: beggarweed, cockcrabgrass, cudweed, dogfennel, johnsongrass, morningglory, ragweed, wild carrot
- Stubby-root nematodes feed on the roots of tomato plants and cause the roots to appear stunted and stubby. The curved stylet that stubby-root nematodes use to feed makes them unique, as other nematodes possess straight stylets. They feed primarily on root tips, causing elongation of roots to stop and making it more difficult for tomatoes to receive adequate water and nutrients. Symptoms of stubby-root nematodes are more severe in sandy soils and generally appear as odd-shaped patches.
Potential host weeds: bermudagrass, St. Augustinegrass, hairy nightshade, bahiagrass
- Fusarium wilt can be identified by yellowing foliage that begins with the lower leaves and progresses up the plant. Infected leaves start curling downward, turning brown and eventually dying. Wilting of the vine becomes progressively worse as time passes until becoming permanently wilted. Fusarium wilt can greatly reduce yields and can survive many years within the soil.
- Pythium root rot, also known as stunt disease, causes plants to be unable to respond to nitrogen fertilizers, reducing yield in the process. It thrives under cool, wet conditions with excess water and poor drainage generating model conditions. Symptoms include blackened, decaying roots and wilted, yellowed foliage.
- Rhizoctonia are fungi that live in the soil and infect seedlings of many crops. Rhizoctonia can infect seedlings before or after plant emergence, resulting in stem lesions found near the soil surface. Lesions can appear red, orange or brown, with older lesions eventually rotting the outer portion of the stem.
- Phytophthora root rot, also known as Buckeye Rot, often develops on tomatoes near the low, wet spots within a field. Early symptoms include small stains on the surface of the tomato that can enlarge and spread to other fruit once stored. As the spot enlarges, brown and light-colored concentric bands form around the fruit, resulting in rapidly decaying fruit. Phytophthora root rot is rare during normal growing seasons, but becomes more common during unusually wet periods.