Seminole Crop E News

Agricultural News for Farmers and Agribusiness in SW Georgia

Canola Sclerotinia Problems

Posted by romeethredge on March 12, 2015

We are starting to see Sclerotinia Stem Rot in Canola now. It can be a very serious disease here in the winter. Fortunately we don’t see it in our summer crops this far south. We often spray a fungicide to help control it.

Consultant Wes Briggs sent me this photo yesterday showing the readily apparent problem. He says he has been seeing a fair amount of it this week. He saw some last week.

 

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Sclerotinia stem rot, also known as white mold, is caused by the soil-borne fungus Sclerotinia sclerotiorum. It has a wide host range and can attack almost any broadleafed plant, but it is not a problem on grasses. This fungus is active only during cool, wet weather. In Georgia, the fungus is active only during the winter months and has never been a problem on any of our summer crops, although it has been present in the soil throughout Georgia for many years. Infections on canola have not been observed before December, and new infections are rarely seen after April.

The fungus survives the hot summer months as sclerotia in the soil. Sclerotia can survive for a year in southern Georgia soils and for up to 2 years in northern Georgia with no decline in viability. Viability declines over subsequent years. Any time during the winter, if the soil becomes very wet for several days, sclerotia can germinate in two ways: by producing mycelium in the soil or by producing small mushroom-like apothecia that produce spores above the soil surface. These spores are disseminated by wind and rain to other parts of the field or to adjacent fields.

Neither the mycelium nor the spores can invade a healthy canola plant directly. Both must become established in dead organic matter in contact with healthy tissues to initiate disease. Once a disease lesion is initiated, the fungus secretes acids and enzymes that kill additional plant tissues. The fungus can rapidly destroy small plants or girdle the stem of large plants if the weather remains wet and cool.

There are no canola cultivars with resistance to stem rot and, in very wet seasons, some plants may be killed in any field in Georgia. In drier years, fewer plants will be killed by this disease. Poorly drained fields suffer losses much more frequently than well-drained fields. The most important control measure is to select well drained fields that have not had canola or another susceptible crop for the past two winters.

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