How to Kill Mealybugs but Save the Tree

Mealybugs are not that particular about the type of trees they like to infest. Deciduous, nut and fruit trees are all susceptible to mealybug infestation. Mealybugs harm trees by sucking the sap out of foliage. Also, mealybugs secrete a sticky substance called honeydew, which coats leaves and bark. Fungal spores flying in the wind attach themselves onto the honeydew. The result: a tree covered in a black powdery substance called sooty mold. Gardeners must use safe cultural and chemical control options to prevent harming their tree.

Things You'll Need

• Garden hose
• Ladder
• Narrow-range horticultural oil
• Pesticides
• Bypass shears
• Pruning saw

Instructions

1. Spray the tree with a strong stream of water to knock off some mealybugs and remove sooty mold. Use a ladder to spray the tree from above to force mealybugs off foliage.

2. Apply a narrow-range horticultural oil to the tree. If you are spraying a fruit or nut tree, use the narrow-range oil when the plant is still dormant. Narrow-range horticultural oil kills mealybugs by smothering them; therefore, they must be used when mealybugs are active or when air temperatures are over 60 degrees Fahrenheit.

3. Water the tree to keep it from getting dehydrated from the horticultural spray. Water-stressed trees do not tolerate being sprayed with horticultural oils or pesticides. Keep water off foliage, because the narrow range horticultural oil is less effective if the tree gets wet within 24 hours of the application.

4. Dilute a pesticide containing buprofezin according to the directions. Spray trees with the pesticide in the summer. Move branches and foliage over to get spray into tree wounds or branch crotches where mealybugs colonize. Reapply every 21 days or according to the directions on the packaging.

5. Prune off heavily infested leaves to reduce the mealybug population. Remove damaged areas of the tree with bypass shears or a pruning saw.

Tips & Warnings

• Prevent harming your tree by refraining from using horticultural oil when air temperatures exceed 100 degrees Fahrenheit.

• Avoid using horticultural oil on trees sensitive to the spray such as junipers, douglas-fir, maples, black walnut and smoke trees to name a few.

References

• University of California-Davis, Integrated Pest Management; Vine Mealybugs; October 2008
• Colorado State University Extension; Insect Control: Horticultural Oils; W.S. Cranshaw and B. Baxendale
• Washington State University Extension; Apple Mealybug; Elizabeth H. Beers