Rhizoctonia Belly Rot of Cucumbers

More commonly found in the Southern United States, Rhizoctonia Belly Rot has been identified in certain Southwestern Ontario cucumber fields for the second year in a row.  The pathogen, Rhizoctonia Solani, thrives under hot, humid weather conditions.

In cucumbers, the infection typically occurs on the underside of the fruit, or where the blossom-end rests on the soil surface or on decaying plant material.  Under suitable conditions, symptoms appear in as little as 24 hours.  Affected plants develop irregular-shaped, yellow-brown discoloured patches.  The infected area does not usually penetrate below the skin of the fruit.  As the lesion dries, it develops a scab-like appearance.  Occasionally, fruit fly maggots may be found feeding on the damaged area.

This disease is difficult to control with standard foliar fungicides.  Protective sprays are unlikely to reach the lower surface of the fruit, where the infections typically occur.  Crop rotation with non-cucurbit crops, and deep plowing of infested residue help to reduce the risk of future infections.

Rhizoctonia Belly Rot of Cucumbers
Figure 1. Typical Belly Rot Symptoms in Cucumbers

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