ATTRA Question of the Week

T.S.
Nevada

Answer: There are different forms of Fusarium disease in tomatoes: Fusarium wilt and Fusarium crown and root rot.

Fusarium wilt, caused by the fungus F. oxysporum f. sp. lycopersici (FOL), produces less extensive discoloration in the plant's water-conducting tissue than Fusarium crown and root rot; the brown streaks extend less than 20 to 30 cm. (8 to 12 in.) above the soil line. Fusarium crown and root rot is caused by the fungus Fusarium oxysporum f. sp. radicis-lycopersici (FORL). Crown and root rot is more likely with cool temperatures (10°C to 20°C/50°F to 68°F), low soil pH (acidic), ammoniacal nitrogen, and water-logged conditions. Since your soils are likely on the alkaline side and generally not waterlogged, it is likely that you have Fusarium wilt (FOL).

Crop rotation for 4 to 6 years is a possible control measure for both diseases, but success is not assured. Practice sanitation in the garden by destroying any infected plant debris. The best method of control is to plant resistant varieties. Some Verticillium wilt and Fusarium wilt (VF) resistant tomato varieties are listed below.

Better Boy
Heinz 1350
Beefsteak
Roma VF
Big Girl
Rutgers
Campbell
Springset
Floramerica
Supersonic

Research has shown that non-pathogenic strains of Fusarium oxysporum—particularly Isolate CS-20—can protect against low pathogen innoculum densities (Larkin et al., 1997). CS-20 apparently triggers development of systemic acquired resistance in the infected tomato plant, thereby making the plant more resistant to subsequent infections of pathogenic forms of F. oxysporum. Unfortunately, there are no commercial products available that use the non-pathogenic forms of this fungus at present. Some (but by no means all) commercially available formulations of bacteria or fungi that have shown effectiveness against Fusarium are listed below. Make sure you check with your certifier to learn which products are allowed for use in organic systems.

*OMRI: Organic Materials Review Institute is a 501 (c)(3) nonprofit. Its mission is to provide professional, independent, and transparent review of materials allowed to produce, process and handle organic food and fiber.

In combination with applied materials, cultural controls are important components of any sustainable agriculture system. Cultural controls include:
+ Use disease-free transplants and seed
+ Use planting stock resistant to Fusarium.
+ A 5-7 year rotation away from hosts.
+ Use nitrate nitrogen rather than ammonium nitrogen.
+ Use localized fertilizer placement to feed the plants rather than the fungus.
+ Do not flood irrigate or use pond or ditch water to irrigate. Well water may be preferable, as it’s less likely to contain Fusarium propagules.

An effective strategy to help destroy Fusarium innoculum is to solarize your soil. The basic technique entails laying clear plastic over tilled, moistened soil for approximately six to eight weeks. Solar heat is trapped by the plastic, raising the soil temperature and destroying the innoculum. The incorporation of poultry litter prior to solarization, or use of a second layer of clear plastic, can reduce effective solarization time to 30 days. (Brown et al., 1989; Stevens et al., 1990) Brassica residues are also known to increase the solarization effect, in a process known as biofumigation. The plastic holds in the gaseous breakdown products of the brassica crop (or food processing wastes), thereby increasing the fumigation-like effect. (High microbial activity has been reported to suppress Fusarium wilt, so maintaining healthy soils with sufficient organic matter to support high microbial populations is another form of cultural control. A University of California Cooperative Extension leaflet (No. 21377), "Soil Solarization: A Nonchemical Method for Controlling Diseases and Pests," details the technique:
ANR Publications, University of California.
6701 San Pablo Ave.
Oakland, CA 94608-1239
510-642-2431; 800-994-8849
www.anrcatalog.ucdavis.edu

The Web site www.uckac.edu/iwgss provides links to current research and publications on solarization.

References:
Borrero, C., M.J. Infantes, E. Gonzáles, M. Avilés, J.C. Tello. Relation Between Suppressiveness to Tomato Fusarium Wilt and Microbial Populations in Different Growth Media

Brown, J.E. , M.G. Patterson, and M.C. Osborn. 1989. Effects of clear plastic solarization and chicken manure on weed control. p. 76–79. In: Proceedings ofthe 21st National Agricultural Plastics Congress. Nat. Ag. Plastics Assoc., Peoria, IL.

Gamliel, A., and J.J. Stapleton. 1993. Characterization of antifungal volatile compounds evolved from solarized soil amended with cabbage residues. Phytopathology. Sept. p. 899–905.

Larkin, R. P. and D. R. Fravel. 1997. Biological Control of Fusarium Wilt of Tomato Under Varying Environmental Conditions.
www.epa.gov/ozone/mbr/airc/1997/036larkin.pdf

Roberts, P. D., McGovern, R. J., and L.E. Datnoff. 2001. Fusarium Crown and Root Rot of Tomato in Florida. Plant Pathology Department, Florida Cooperative Extension Service. Publication PP-52. http://edis.ifas.ufl.edu/PG082

Stevens, C., V.A. Khan, and A.Y. Tang. 1990. Solar heating of soil with double plastic layers: a potential method of pest control. p. 163–68. In: Proceedings of the 22nd National Agricultural Plastics Con gress. Nat. Ag. Plastics Assoc., Peoria, IL.