Pictured above: Hawthorn mealybug adults circled in yellow. Hawthorn leafminer insect damage circled in blue.

A major pest almost unique to the Front Range of Colorado: the hawthorn mealybug. We don’t really know why it likes it here so much, but it is far less common or nonexistent in other parts of the country. This insect can do serious damage to the tree, including mortality. It also drips honeydew which attracts yellowjackets and wasps, and causes staining on hard surfaces under the tree. Control of this pest can be difficult and requires yearly pesticide applications on the most susceptible trees. In 2014 I began treating for this pest with a new (bee friendly!) product and have had excellent results; I intend to keep the secret to myself for the time being.

Hawthorns most susceptible to mealybug (most to least):

  • ‘Toba’ English hawthorn
  • English hawthorn (other)
  • Thornless cockspur hawthorn
  • Arnold hawthorn
  • Black hawthorn
  • Russian hawthorn (fairly resistant)
  • ‘Cordata’ Washington hawthorn (very resistant)

If you're planting a new hawthorn you'll want to take this into consideration.