This fungal disease caused by Taphrina communis is common on plants grown in Saskatchewan.
Symptoms
This disease affects the leaves, shoots and fruits. Symptoms on fruit are visible soon after fruit set. The fruit becomes very large, sometimes ten times normal plum size, hollow (without pits) and bladder like. They are yellow at the start but soon turn red and later powdery grey. Affected twigs are swollen and distorted, and affected leaves are malformed and curled.
Disease Cycle
The fungus overwinters on infected twigs and buds and the disease is spread by spores in the spring shortly after the blossom buds open. Cool, wet conditions during this period are necessary for infection.
Control
- Prune back infected branches and burn these along with any other affected fruits and twigs that can be gathered. This will eliminate much of the source of inoculum. Large pruning wounds should be covered with a wound dressing such as Braco, shellac or other reliable wound dressing product available from seed and garden supply dealers.
- In addition to pruning, a dormant spray with a fungicide will help control plum pockets. Use one of the following sprays: 2 tablespoons per gallon of thiram, or a lime-sulfur solution (1 part lime-sulfur to 9 parts water) or 8:8:100 Bordeaux mixture (see below). The timing of the application is important to get effective control and not damage the plants. Spraying should be done just before the buds open. When the flower buds are at the popcorn stage and again just after the petals fall, a spray with lime-surfur at 4 pounds in 100 gallons or wettable sulfur at 4 pounds in 100 gallons, have also been recommended. When using chemical control read the product label carefully and follow directions on use and on handling precautions.
Bordeaux Mixture - A small volume of 8:8:100 Bordeaux mixture is made by dissolving 4 ounces of copper sulfate (Bluestone or Blue Vitriol) in one gallon of water and 4 ounces of calcium hydroxide (hydrated or slaked lime) in 2 gallons of water. Pour the copper sulphate solution into the lime water and strain through fine cheesecloth. Use the solution immediately after mixing and also, fresh lime solution is essential, not some left over from the previous season.