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Fielding Questions: Tent caterpillars, hydrangeas and a lawn killed by herbicide

Don Kinzler, Growing Together and Fielding Questions columnist. The Forum1 / 2
A Moorhead resident asks for help figuring out the culprit behind these translucent "bags" attached to branches of their flowering crab. Special to The Forum2 / 2

Q: We have a beautiful 8-year-old flowering crab in south Moorhead. We found three different spots with this translucent “bag” 6 to 8 inches long attached to a branch, with worms both inside and outside the bag. We snipped the branch off below that area. Do you recognize the culprit, and should we do anything more to protect our tree? — Ricki and Dave Shaw, Moorhead, Minn.

A: These are the nests of tent caterpillars, which leave the nest during sunny days to feed on leaves. Their feeding can be quite serious and can defoliate trees, which especially weakens young trees.

The tents can be pruned out, as you’ve done. The caterpillars can also be controlled with insecticides. Bacillus thuringiensis, with brand names like Dipel and Thuricide and abbreviated BT, is a good option. This bacterial spray will only kill caterpillars; it is harmless to people, bees and wildlife. Spinosad is another recommended insecticide that is less harmful to non-targeted life. BT is less effective if caterpillars have reached their full size of 2 inches, in which case chemical insecticides such as carbaryl (Sevin) and malathion are better choices. Spray the caterpillars, tents and surrounding 2 feet of area around the tents.

According to the North Dakota State University Extension, if left alone the caterpillars will stop eating after a few weeks and then rest inside a yellowish cocoon on tree trunks, fences or other support structures. The adults will emerge later this summer and lay eggs for next spring’s hatch.

Q: I have tried planting three different hydrangea bushes in my flower bed, and none have survived. Do you have any tips for getting one started? I have two spots for it, one south-facing with mostly full sun, the other west-facing with a little morning shade. I’d like the ones that have the large white flowers. — Laura Oster-Aaland, Christine, N.D.

A: Two favorite hydrangea cultivars with large white flowers are Annabelle and Incrediball, which are both types of Hydrangea arborescens and well-adapted. Hydrangea means "water-loving." Their preferred locations are east and north exposures, which are naturally moister and cooler than south and west exposures. Hydrangea arborescens types grow well in shade or half-day shade.

If your only choices are south and west, there are still ways to grow these hydrangeas, so don’t give up. First, incorporate a generous amount of peatmoss into the planting bed to help retain moisture and cool the soil. After planting, mulch the soil with a 5-foot diameter circle of shredded bark 5 inches thick. Water religiously and deeply throughout its life when hydrangeas are in sunny, warm spots. By following these guidelines, hydrangeas are successfully grown, even in less-than-idea exposures. Without these measures, hydrangeas suffer in hot, sunbaked soil.

Q: We sprayed our rural lawn with a mixture of GlyStar and 2,4-D for weed control. The lawn is now totally brown. We’ve been watering and watering, but it looks dead. Do you have any idea what we can do to fix the problem? — Name withheld, South Dakota.

A: In researching GlyStar's label, its active ingredient is glyphosate, which is the same ingredient in original Roundup, which kills most green plants it touches, including lawngrass. The GlyStar label gives this caution: "IMPORTANT: Do not spray plants or grasses you like — they may die, too. Not recommended for spot weed control in lawns because GlyStar Concentrate kills lawn grasses."

Most lawns have little or no hope of recovering from glyphosate, leaving reseeding as the only option. You can mow very short, and then seed directly into this stubble. The stubble will give some protection for the new seedlings. You might power rake the lawn before seeding to remove thatch and allow the grass seed to have better contact with soil. Watering will be very important, as always, for germination of the new grass seed.

This unfortunate situation is a good example of reading product labels very carefully, and using farm-type herbicides on lawns only if the label specifically lists lawns and provides a usage rate.

If you have a gardening or lawn care question, email Don Kinzler at ForumGrowingTogether@hotmail.com. All questions will be answered, and those with broad appeal may be published, so please include your name, city and state for appropriate advice.