Plant and Insect Diagnostic Clinic Update - September 10, 2008

The following are a few of the problems received the past two weeks.


  • Crane flies are large, fragile-looking insects that look like giant mosquitoes thought they are not closely related. See the photo below. Crane flies are harmless. They have no mouthparts; they do not eat and they cannot bite. They also have no stinger. Like all flies, the crane flies have a complete life cycle (egg, larva, pupa, adult). The larvae are fat, legless maggots that live in mud where they feed on decaying organic matter. Crane flies are moderately common but harmless. No control is needed.
  • Yes, Virginia, it is too late to spray for bagworms. Spraying this late in the season, after the caterpillars have fed and grown and after the damage is done is worse than a waste of time and money; it is environmentally disruptive with no offsetting benefit to the tree or the property owner. By now the caterpillars have finished feeding (no additional damage to the tree!) and have tied the bag to a twig before sealing it shut. Insecticide sprays have no effect after the bags are tied to the twigs. The caterpillars must be exposed at the open ends of the pods and actively feeding for insecticides to be effective. Mark your calendar to check for small caterpillars next June and spray then if caterpillars are present. The bags hanging on the trees contain the eggs for the next generation (they will hatch next year). These can be removed from small trees by hand and discarded anytime between now and next spring. Some people find it easier to use scissors to cut bags from the trees rather than trying to pull them off and damage the foliage. Removed bags can be burned if open burning is allowed, buried, or soaked in a bucket of detergent water.
  • Yellowjacket wasps continue to attract attention as the colonies are now at maximum size and there is more activity at nest openings in the ground or in house, foundation or retaining walls. See the August 13 Horticulture and Home Pest News for details.

A pair of crane flies, as seen through the screen door.

A pair of crane flies, as seen through the window.


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