I live in Belle River, Ontario. The plums in my back yard are green; when they turn red the plums have worm holes and other bug holes inside is all rough. What can I do?
Thank you for your question.
Although plum trees are less plagued that other kinds of fruit, there are some pests which afflict.
From your picture and description the problem you have may be the larva of the Oriental Fruit Moth, which unfortunately is a problem in south western Ontario. This pest is evidenced by holes in fruits and internal damage to the fruit.
Try to limit the spread of the larva by collecting all damaged fruit from on or below your plums. There are extremely limited options available to the home gardener under Ontario’s Pesticides Act which might help . You can apply a permitted insecticidal soap in accordance with instructions.
Here is information from the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) on this pest and the home gardener: