Caring for plum trees involves spraying them for a variety of pests and other problems like fungi, including brown rot, which can destroy a whole crop of fruit. Applying sprays to a plum tree at the right time is part of regular tree maintenance and keeps the plum tree healthy and productive.

Winter or Early Spring

Along with pruning the plum tree in late winter or early spring, agricultural fungicide spraying an organic dormant oil spray during the winter or spring helps protect the tree's wounds and kills off any remaining eggs from the previous season's pests. Before spraying the oil, removing any dead branches and clearing away debris like leaves and fallen fruit from around the base of the tree is key to keeping the tree healthy. Dead organic matter provides a habitat for harmful insects that the oil spray may not catch.

Early Spring

Once leaves begin to emerge on the plum tree, a fungicide should be applied to the whole tree, including the blossoms. Fungicides help control fungal diseases like brown rot, which attack the blossoms first. Other fungal diseases that affect plum trees include anthracnose and root rot. Protecting the plum tree from these fungi with a fungicide spray keeps the tree healthy. Apply fertilizer around the same time to give the tree the nutrients it needs for spring growth.

Summer

Continue applying a fungicide and pesticides throughout the summer, especially once fruit begin to appear. Insects attack the forming fruit and leave the plum tree susceptible to invasion by fungi; this is especially true of fallen fruit, which can become hosts for fungi over the winter. Remove fallen fruit and apply fungicides and pesticides frequently and according to the directions on the bottle. Avoid spraying the tree within a day before rainfall, as the rain will wash the spray from the tree.

Autumn

Once the tree has produced its yield of plums, dropped most of its leaves and is becoming dormant, the final spray of the season can be applied. Remove any fallen leaves or remaining fruit from around the tree. Spray a fixed copper spray on the plum tree. Copper sprays are effective at preventing fungi from forming and protect the tree over the winter and its dormant period. Spray the fixed copper spray over the whole tree.