When should you spray fruit and plum trees for insects?

Plums are deep purple fruits native to China, North America and parts of Europe. They are available in two main varieties: Japanese plums, which thrive in warm southern areas; or European, which do well in the north. Trees range in height from 2.4 to 10.5 m (8 to 35 feet) and can spread up to 6 m (20 feet). Plum trees are susceptible to a variety of pests and diseases that can be prevented by timely application of insecticides.


Depending on the variety, plum trees will do well in most climates. They require nutrient rich. well-drained soil and should be planted in a location that will provide at least moderate sun. There are some 200 types being grown today, some of which will self-pollinate. Most will produce fruit between three and five years after planting. Planting should be done after the last frost of the year, as seeds and blooms are extremely sensitive to cold. Once established, growers should maintain moist soil and prune away dead or damaged branches.

Red spider mite

Red spider mites are a fairly common affliction among plum trees of Japanese and European varieties. Early signs of infestation will see leaves begin to brown. A fine white web can be seen on the leaves. Growers can look closely and see the tiny insects crawling on the undersides of leaves. Because these common garden pests are resistant to most insecticides, giving the tree a spray with a medium-pressure nozzle will help control the problem.

Other pests

Though plum trees may be affected by a variety of pests and diseases, there are two in particular that are common. The plum sawfly is a destructive insect that lays eggs on blossoms during the spring so they can tunnel into the fruit once hatched. After the fruit is infested, growers will notice holes in the fruit, which will ooze with a dark-coloured liquid. To aid in prevention, turn the soil in the autumn to expose sawfly pupae to cold temperatures, making them unable to lay eggs in the spring. Aphids are another serious pest. They are rarely fatal, though growers will notice a general decline in health as the insects feed on the tree sap, which will rob much-needed nutrients from new and existing growth.

Pest control

Infestation prevention is an important step in caring for a plum tree. Aphids can be killed by spraying the tree with a mixture of water and washing up liquid, or they can be naturally killed by introducing ladybirds. For a severe case of aphids or sawflies, an application of insecticide may be necessary. The best time to apply this spray depends on the region. Warmer climates will benefit from an early to mid-spring spray as the petals begin to drop. For cooler climates, August, September and October are more appropriate. These timetables will ensure eradication of eggs and larvae before they have a chance to feed on fruit.

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About the Author

Sara John is a professional writer and copy editor living in Des Moines, IA. She has worked professionally for seven years, and written articles for the Long Beach Press-Telegram, as well as other local publications. She is a graduate of Grand View University and holds a B.A. in journalism.