Borers list long but exciting

No yawning over these bugs yet they do bore

Various insects are called borers, in recognition of their method of entering their home. They chew their way into a branch, twig, leaf stalk, root, etc. Some are weevils (immature beetles), many are caterpillars and even a few maggots (fly larvae) follow this lifestyle.

Most borers are attracted to weak plants, perhaps by telltale smells or visual signals. The adults lay eggs in opportune places, such as weak crotches or soft new tips, where thin bark or splits in wood and weak cell walls will give way easily to tiny chewing mouths of insects just emerged (eclosed) from eggs.

The symptoms: Plants attacked by borers most often give us notice of the attack by general weakening, yellowing, wilting -- especially during stressful hot periods -- and undersized leaves and few flowers.

So the first line of defense against borers is to keep a plant growing well, in a situation that promotes fast , strong growth and quick replacement of parts lost to borers.

If general plant health improvement doesn't curtail borer damage, the next tactic is to try to kill the young as they emerge. It's the old "aim at the weakest link" strategy. Older borers are usually protected within the plant, unreachable to our chemical killers or in resting/transformational stages when poisons that must be ingested can't affect them. But the first attack comes from exposed eggs, which can be killed with a smothering oil applied at the right time, or an insecticide that will coat the plant in those places borers will chew. This tactic requires knowing what kind of borer, to know the life cycle -- especially when egg laying occurs.

We've covered numerous borers in our time on this beat but we'll probably never  cover them all. Too many plants and plant groups, each with their own borer -- species that evolved together.

If you suspect borers are at work -- exit holes in bark being one sign -- search a plant health management index or the Internet using plant scientific name followed by the word borer. Select .edu sites for Extension bulletins, .gov for foresetry and agriculture department reports, etc.

Here are links to some borers we've covered, and back issue numbers to look for.

  • Dogwood borer (attacks many plants including hydrangea) What's Coming Up 140
  • Emerald ash borer (devastating to true ash, Fraxinus species, in North America) What's Coming Up 36, What's Coming Up 39 and What's Coming Up 86
  • Lilac/ash borer (may feed on certain other plants) What's Coming Up 63, What's Coming Up 114
  • Pine borer, What's Coming Up 41
  • Rhododendron borer, What's Coming Up 11
  • Rose/Bramble cane borer, What's Coming Up 40
  • Viburnum borer, attacks trunk, What's Coming Up 92
  • Viburnum tip borer, What's Coming Up 138

An issue number without a link means the issue was not yet up on the site when we wrote this. Check the Ensemble Weekly Edition section cover page where back issues are listed, for that issue's status.

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