Timber Rot on High Tunnel Tomatoes
Posted: June 2, 2014
Timber rot, which is also known as white mold or Sclerotinia rot, has been a problem in tunnels periodically in the last few years. This disease has a wide host range and can survive in the soil for many years. Symptoms on tomato most commonly are the random collapse of entire plants as infections usually occur close to the soil line. However, when conditionals are ideal (as was often the case this spring) any part of the plant can be infected including upper stems, leaf petioles, and even the fruit itself. Under conditions of high humidity a white mold will appear on the infected area; under drier conditions the affected area will turn a light tan color. Large black structures called sclerotia will develop in the infected areas, either inside or on the outside of the stem. These sclerotia can survive in the soil up to 10 years depending upon soil conditions.
The most important method for control of timber rot starts with sanitation after any infections occur. Remove and bury or destroy infected tissue before the sclerotia have a chance to fall to the soil. Since the spores that caused this disease most likely blew into the tunnel from nearby, sanitation around the outside of the tunnel is also important. There are a few fungicides labeled for control of timber rot but the problem is knowing when to apply these products. If you know that there may be sclerotia in your soil the most practical product to use next season is Contans which contains a microparasite that will attack the overwintering sclerotia. Contans needs to be applied 2 to 3 months before you plant your crop in order to be effective. Crop rotation, while practical in the field (switch to corn or a small grain) is not a likely control in a tunnel because of the wide host range of this disease. So it is critical that you reduce the chances of the disease overwintering in the tunnel in order to most successfully control timber rot next year.