Spray plum trees right before new growth develops with a fungicide, horticultural oil and dormant spray, according to North Dakota State University. This prevents various funguses and insects wintering on the tree from developing when warm weather returns. Identify any problematic insects infesting the tree and spray with an approved insecticide for plum trees, as the problem occurs.
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Joyce Starr is a freelance writer from Florida and owns a landscaping company and garden center. She has published articles about camping in Florida, lawncare, gardening and writes for a local gardening newsletter. She shares her love and knowledge of the outdoors and nature through her writing.