Dormant Oil Spray

• Dormant oil sprays, applied in winter, prevent diseases like powdery mildew. They also kill the various insects that overwinter on the fruitless plum tree, such as aphid eggs and scale. Since the oil kills the pests by smothering them, it is important to ensure that all parts of the tree are covered with the spray. Do not apply the dormant oil during periods of freezing temperatures or when it has recently rained or rain is expected.
  
  

Fungicide Spray

• Black knot is a common fungal disease of fruitless plum trees. When infected, the plum tree's twigs swell to several times their natural size and turn dark brown to black. The knots girdle the twigs, causing dieback. Although part of managing the disease involves pruning the tree and sanitary cultural practices, fungicide spray also is part of the treatment. Use a fungicide containing chlorothalonil or mancozeb and copper hydroxide. All parts of the fruitless plum tree should be covered with the spray. Consult the fungicide label for mixing rates and application instructions.
  
  

Insecticidal Spray

• Leafrollers are common on many fruit trees and fruitless ornamentals. To control them, use an insecticide containing the bacterium Bacillus thuringiensis, commonly called "Bt." It only kills the leafroller in the larval stage, so timing of the application is critical. Apply the insecticide when the leafrollers hatch, or immediately thereafter. Inspect the tree frequently to look for the small caterpillars. Use a high pressure sprayer, either a power tank or hose end sprayer, to get inside the rolled leaves. As with the other sprays, thorough coverage of the tree is required and you may need to reapply, as the label instructs. Shortly after spraying Bt on the fruitless plum tree's foliage, the leafrollers become infected and stop feeding. They die a few days later.
  
  

Considerations

• While many fruitless plum tree spray products are organic and safe, others may be may be irritating to your skin and eyes so wear eye protection, gloves and a long-sleeved shirt during application. Read the entire label before application and follow all of the precautions. Keep children and pets out of the treated area until the spray dries.