Archived Story

Spring tents in apple trees bad

Published 7:06am Monday, April 1, 2013 Updated 9:10am Monday, April 1, 2013

The early bird won’t get this worm. The Eastern tent caterpillar has already defoliated your fruit trees by the time worm eating birds show up in our yards.

The hairy, little stinkers hatch, defoliate your apple tree, molt five times and pupate before any of their predators get out of bed and head north.

This means, you, the apple, plum, cherry, chokecherry or pincherry owner, needs to be out and about checking on your trees as soon as they begin to bud out. This usually happens in early March, but probably not this year, unless the snow melts in a hurry.

The mostly black hatchlings, emerge from an egg mass and immediately start building a tent in the crotch of the tree. This is essentially a greenhouse to keep the cold-blooded worms above 60 degrees.

Cooler than that and they can’t digest the leaves they remove from your trees. This tent is added to every day by the 200 or so caterpillars that have just taken over your tree.

The caterpillars leave the tent three times a day to feed — early morning, mid-afternoon and dusk, creeping back to the tent after each expedition. Now is the best time to remove them.

Put on a glove if you are a little finicky, go out before breakfast and simply pull the tent out of the tree. Squish the tent well to kill all the crawlers.

Whatever you do, do not set fire to the tent. While this does dispose of the caterpillars, it also damages your tree.

If you overlook a tent, and the caterpillars have changed from little black critters into 2-inch-long fellows with a set of blue marks on their sides and a white strip on their back, you have a bigger problem.

They are now no longer feeding in clumps, but separately, and worse yet, at night.

At this stage, they are ready to pupate. The adult is a nocturnal moth that lays a shiny black mass of eggs on the smaller branches of the tree.

If you had tent caterpillars last spring and you can get to your trees, look for these egg masses.

Clip off the branch with the mass on it, bag it and burn it if you can. If you are too late and you see the small black caterpillars on the tree, and are too squeamish to scrunch them, you can spray the emerging leaves with B.T.

B.T. is short hand for Bacillus thuringienis, var. (short for variety) Kurstaki. This is only effective if the worms eat the leaves. The B.T. paralyzes the gut so the affected caterpillar starves to death. This pesticide can be used for any leaf-eating caterpillar.

Most trees are damaged early enough in the season that they can recover and send out another flush of leaves.

These, however, may be smaller and fewer as the tree has already expended energy to do this once.

The moral of the week is: if you want fruit trees, don’t share them with caterpillars.

Reminder: Garden Day 2013 is Saturday, April 6, at Kennedy Secondary School in Fergus Falls. Want to see a preview of classes? The brochure is on the following website, http://www.extension.umn.edu/county/ottertail, ‘Hot Topics in Otter Tail County.’ Don’t miss it!

 

Bev Johnson is a master gardener in Otter Tail County.

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