Diseases of tomato (
Fusarium wilt
Fusarium wilt of tomato, caused by the fungus Fusarium oxysporum f. sp. lycopersici, is generally found only in greenhouses in Arizona. It is problematic only on susceptible species.
F. oxysporum f. sp. lycopersici is a wilt pathogen that invades the xylem, the water conducting tissue of the plant. Discoloration of the xylem is characteristic of disease. Wilting is usually noticed during the day and the plant also may be stunted.
Symptoms begin with yellowing of older leaves affecting an entire branch that produces a “yellow flag” appearance. The affected leaves wilt and die although they remain attached to the stem. A characteristic red-brown discoloration of the vascular tissue extends far up into the plant and is evident if a stem is cut. F. oxysporum f. sp. lycopersici is soilborne and remains in infested soils for several years. It usually enters through wounds in the roots.
There are no effective treatments once plants are infected, so sanitation is extremely important for prevention and control. Look for resistant varieties when re-planting previously infected areas. Use only healthy disease-free transplants; disinfect all planting tools and media and greenhouse benches and structures.
Fusarium wilt is uncommon on tomato in Arizona and is often misdiagnosed. The most common cause of wilting of garden tomatoes in Arizona is tomato russet mite. Fusarium wilt can be distinguished from russet mite damage since Fusarium wilt causes plants to wilt from the top down or branch by branch and exhibits xylem discoloration while mites cause tomatoes to yellow and wilt from the bottom up and there is no xylem discoloration. Russet mite can be controlled with applications of sulfur.
Links to images and additional information:
http://www.ipm.ucdavis.edu/PMG/r783101011.html
http://vric.ucdavis.edu/veginfo/commodity/tomato/tom9.jpg
http://www.ipm.ucdavis.edu/PMG/F/D-TO-FOXL-FS.002.html
http://www.oznet.ksu.edu/dp_hfrr/extensn/problems/tomwilt.htm
Comparison with tomato russet mite:
http://www.ipm.ucdavis.edu/PMG/r783400111.html
http://cals.arizona.edu/urbanipm/mites/tomatorussetmites.html
January 8, 2007