Root Rot in Tomato Plants

Tasting sweet, salty and earthy all at once, red, ripe summer-garden tomatoes far outshine their anemically flavored, midwinter grocery-store counterparts. Growing tomatoes (Lycopersicon esculentum) successfully at home, however, can be a challenge thanks to soil-borne, crown- and root-rotting Fusarium fungus. Even container-grown tomatoes aren't exempt from the disease, which thrives in wet conditions. No treatments cure Fusarium root rot, but several cultural methods help stop its spread.

Fusarium-infected tomatoes are often noticeably smaller than healthy ones of the same variety. If they live long enough to bear fruit, their lower leaves wilt and yellow as daytime temperatures peak, and recover from wilting as they cool off. Some of them struggle on, producing small crops of poor-quality tomatoes. Others collapse to the ground and die.

Dark-brown swellings, or cankers, at the base of an infected tomato's stem confirm a Fusarium diagnosis.

Cool, wet weather with temperatures in the 50- to 68-degrees Fahrenheit range invites Fusarium to run rampant in the tomato patch. When rain is absent, however, overgenerous watering is enough to awaken the fungus.

For healthy growth, tomatoes need only 1 inch -- 2 inches where summers are very hot and dry -- of weekly rain or supplemental water. This applies to in-ground and container plants.

Any container used to grow tomatoes needs drainage holes. Drill them if necessary  

Providing tomatoes more water than they actually need won't help them grow more quickly, but it might drown their roots in addition to raising their risk of Fusarium infection.

One inch of water equals about 6 gallons per 10 square feet.

Use a rain gauge to track your weekly rainfall. At the end of each week, give the tomatoes only as much water as they need to bring their weekly total up to 1 or 2 inches. 

Fighting Fusarium root rot begins with removing all infested plants and disposing of them in sealed plastic bags. In the future, plant them in raised beds or in soil amended with drainage-improving organic material. Choose a location with no previous history of Fusarium infestation; infested soil may harbor the fungus for years.

If possible, plant Fusarium-resistant cultivars, such as 'Baby Cakes' (Lycopersicon esculentum 'Baby Cakes'), 'Clermon' (Lycopersicon esculentum 'Clermon') or 'Basket Vee' (Lycopersicom esculentum 'Basket Vee').

Fusarium gets into a container's growing medium by hitchhiking on the roots of an already-infected tomato, or on tools previously used to work contaminated garden soil and not disinfected afterwards. Once there, it spreads with the help of excessive water or inadequate drainage holes. Once contaminated, the potting mix and container are potential sources of reinfection. The safest course is to dispose of the plant, container and all, in a sealed plastic bag.