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Timber rot on tomato

Posted: July 28, 2011

Symtpoms of timber rot on a tomato stem. Sclerotia, the overwintering survival structure, develop as the plant tissue dies. When these sclerotia fall to the soil, they can survive for up to 10 years depending on soil conditions. Photo: Beth K. Gugino

Symtpoms of timber rot on a tomato stem. Sclerotia, the overwintering survival structure, develop as the plant tissue dies. When these sclerotia fall to the soil, they can survive for up to 10 years depending on soil conditions. Photo: Beth K. Gugino

Timber rot otherwise known as white mold or Sclerotinia rot is becoming an increasingly serious problem especially in high tunnels. Although it may only affect 5 to 10% of the plants in any one season, it could have long-term affects because of its wide host range which includes many vegetable crops and its ability to survive for extended periods in the soil.

Timber rot is caused by the pathogen Sclerotinia sclerotiorum. The symptoms are initially water-soaked lesions that gradually girdle the stem. Under high relative humidity, white fungal growth can cover the lesions. Large black sclerotia, the overwintering fruiting structure of the pathogen, will develop on the outer surface or in the center of the stems. These structures can survive in the soil up to 10 years depending on the soil conditions.

In high tunnels it is thought that the primary source of the pathogen is probably coming from outside the high tunnel. In the spring, ascospores are released from the fruiting bodies when the soil is moist and carried via the wind into open doors or sides of high tunnels. They are usually carried no further than 330ft therefore sanitation around the high tunnel is critical. Endura is labeled for timber rot in the high tunnel and Botran is labeled for greenhouse use. The biocontrol product Contans has been used to manage Sclerotinia diseases in the field. Contans, which is a formulation of the mycoparasite Coniothyrium minitans, parasitizes the overwintering sclerotia. It is best applied over crop debris around the high tunnel in the fall or spring 2 to 3 months before planting the crop. See the label for additional information (http://www.cdms.net/LDat/ld5SH000.pdf).

This season, infected tomato plants should be carefully removed from the high tunnel to ensure that the sclerotia do not fall into the soil. Also remove the soil surrounding the plant to remove any sclerotia that may have already fallen to the ground. Either bury in an area not used for crop production or burn the crop debris. For field tomatoes, rotate to a non-host such as sweet corn or any grain crop.

If timber rot has been or currently is a problem on your farm especially in your high tunnel, please let me know (Beth Gugino at bkgugino@psu.edu or 814-865-7328.). We are interested in trying to better understand the source of the pathogen in an effort to better manage this disease.