Some years are worse than others for certain pests.
In 2012, tulip tree scale was so bad that the sticky stuff coming down from tulip trees was making certain decks unusable and even caused a friend’s pool pump to seize up. Together with the drought that year, the scale was part of a one-two punch that killed many trees. Folks entered the 2013 growing season ready to do battle, but the scales were nowhere to be found.
That’s the nature of things with diseases and pests that bother landscape plants. Conditions one year can cause a population explosion of one pest but not another, thank goodness, or we would be hammered all at once by the lot of them. This year, conditions seem to have favored the tent caterpillars.
If you are not acquainted, tent caterpillars will form webbed tents in the crotches of trees in the spring, from which they will make forays to eat leaves. While they favor trees in the rose family, like apples and cherries, the critters will set up shop just about anywhere.
Tent caterpillars aren’t typically life-threatening to the trees, but a heavy infestation in the wrong place will have residents sweeping up the fallen caterpillars from porches and decks in large numbers. The “ick” factor can be extreme.
The good news is that tent caterpillar season is just about over, and the bad news is that there are lots of other caterpillar species getting ready to hatch. One that is much more damaging than tent caterpillars is the bagworm — the caterpillar that uses those first few bites of your plant to camouflage the Tyvek-like bag that it carries around for shelter. Bagworms are more damaging because their hosts, mostly evergreens, don’t regenerate lost foliage the way deciduous trees can.
You might find a bagworm infestation by discovering that the top of an arborvitae or other evergreen has been stripped of foliage. By then, it is often too late for a full recovery.
Watching for bagworms, especially if you had an infestation the previous year, is a great idea, as they are more vulnerable to controls when they are small. The challenge is that when they are small — smaller than your smallest fingernail — they are hard to spot. May and June is the time!
It might be tempting to pull out the insecticide, but there is a product that works only on caterpillars and protects pollinators such as honeybees. Bacillus thuringiensis (Bt, sold as Dipel or Thuricide) is a bacterial stomach poison — sold as a powder — that kills only caterpillars. Shake it onto the foliage that you want to protect, and caterpillars feeding on it will die. This material is labeled for most caterpillars, even those such as cabbage loopers and tomato hornworms that can be so destructive in the vegetable garden. Always use a product such as this according to the label instructions, of course.
If you keep some Bt on hand, you will be ready for the tent caterpillar’s nearly identical cousin: the fall webworm.
Whatever you do, and even if your Grandpa did this, avoid setting those caterpillar tents on fire. It’s bad for the tree.