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How to get rid of tent caterpillars before they damage a tree

"Fielding Questions" columnist Don Kinzler also addresses why the well-intentioned "No Mow May" movement isn't without controversy.

tent caterpillar June 4, 2022.JPG
A reader asks Don to identify these "worms" on a neighbor's crabapple tree.
Contributed / Special to The Forum
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Q: The attached photo shows worms that are on my neighbor’s crabapple tree. She called them army worms, since she had something similar at the lake on an elm. Do you know what they are? — Kristi M.

A: The worms that build these protective nests are called tent caterpillars. There are several species, but they can be treated similarly. The caterpillars leave the nest to feed on foliage, which can cause damage to the tree if feeding is extensive.

One of the easiest ways to rid the tree of the caterpillars is to wait until the worms are congregated inside the tent, and then scrape away the tent, worms and all, with a stick or other utensil and drop in a bucket of soapy water. Pruning away the branch on which the tent is located isn’t necessary, unless the branch is very small and expendable.

Insecticides are often ineffective, because the tents are difficult to penetrate with the spray. If the caterpillars are outside the tent, the biological insecticide Bacillus thuringiensis can be applied, but the worms must be small and young because the product is less effective on large, older caterpillars.

Click here to read more of Don Kinzler's gardening columns.

Q: I’ve been honoring No Mow May, and now my grass is starting to produce seed heads. What is my next step — cut it as high as the mower will go, or cut it to the normal 3-inch height? When can I cut it? — Morrie S.

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A: No Mow May started several years ago in the United Kingdom as a well-meaning movement to increase pollinator habitat and food sources by not mowing lawns during May. The movement gained traction in the United States during the past two years.

Pollinators are necessary for everything from apples to cucumbers, but the well-intentioned No Mow May movement isn’t without controversy. Not mowing one’s lawn in May won’t automatically turn it into a meadow of nectar-filled wildflowers for pollinators to enjoy. Allowing a lawn to get very tall and then mowing short can stress the lawn, which helps neither the lawn nor the pollinators.

For those who participated this year, it would probably be wise to mow now, before the grass grows taller. The rule of thumb when mowing tall lawn grass is to remove no more than one-third of the grass blade at one time. That often means setting the mower as high as it will go for the first mowing and then gradually reducing the height during the next several mowings to the recommended height of 3 inches.

All of us wishing to help pollinators flourish might consider adding a portion of “bee lawn” to our turf space. A bee lawn patch can be created by seeding white clover, creeping thyme and a plant called self-heal into the existing grass. These bee-friendly plants are low-growing, so lawns can be mowed at the recommended 3-inch height and the plants will maintain their flowers below that level. Bee lawns can provide the best of both worlds; they provide food for pollinators and can still be neatly mowed while avoiding the disadvantages of No Mow May.

Q: When shopping for strawberries, I notice some types are called everbearing and some are called June-bearing. Which do you prefer? — Bill N.

A: June-bearing strawberry cultivars produce a large crop in early summer until about July 4. Everbearing types produce two lighter crops of berries, divided between June and mid-to-late summer.

There are advantages to both types. June-bearing strawberries produce a larger quantity overall, and are the favorite for freezing or processing the berries, because there are more ready at one time. Everbearing types produce less berries overall, but they are preferred for those wishing to spread out the harvest season between two crops.

If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at donald.kinzler@ndsu.edu. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at donald.kinzler@ndsu.edu.
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