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Garden Q&A

Eastern tent caterpillars are relatively harmless

For The Baltimore Sun
What you think are pests may be helpful insects. This week's Garden Q&A deals with two of them.

A 10-inch cocoon appeared, literally overnight, on my cherry tree, and when I broke it open with a broom, to my horror, it was full of large crawling millipedes or worm-like creatures and what seems to be rotting wood. I'm worried it will kill the tree. Is it gypsy moths?

Eastern tent caterpillar nests are a common sight this time of year. They are especially fond of cherry trees, but they are native insects with lots of predators that evolved along with them. A tremendous food source for birds, the caterpillars are only present for a short time, eating a few leaves but rarely harming an established tree. Break up the nest, just as you did, to let predators feed on them, but otherwise leave them alone. The "wood" particles you saw is their excrement.

Black mold is covering the leaves of my holly tree. My research indicates that I need to identify the pest to determine the best treatment. The only insect I can find is a black lady beetle with two red spots. How do I get this mold off the leaves after the pest is eliminated?

Identifying the pest accurately before treating is crucial, and we're glad you contacted us.

The twice-stabbed lady beetle you found is not a pest at all but a beneficial insect eating the true pest. The black leaf mold, known as sooty mold, indicates a sucking insect — in this case a soft scale. Scale insects look nothing like what we think of as insects. They spend most of their lives hiding under a tiny turtle-like shell and sucking plant sap. Then they excrete a sweet liquid called honeydew, which drips on the leaves below. Sooty mold grows on the honeydew. On your leaf underside is the actual scale insect — an oval with a white, cottony egg sack trailing behind it. This is cottony camellia scale. In winter, use a dormant oil spray. In mid-June, monitor leaves for crawlers (the scale's immature, mobile first stage), which have no protective shell. Unless there are lots of lady beetles eating the insects already, apply an insecticidal soap or summer rate of horticultural oil on all leaf surfaces. We don't recommend other pesticides, to protect beneficial insect populations. Rain will wash off the mold eventually.

Digging deeper

Don't be fooled by this vibrant green mound of leaves with its dainty spring flowers. The flowers soon turn into long, slender capsules that explode — spraying seeds that live in soil for years, sprouting and invading your landscape. Garlic mustard is one of the top alien invasive plants in Maryland, especially in parks. A biennial, first-year plants are small and easy to pull or rake out. The second year, when mature plants bloom, be sure to get the entire root when you pull or dig it up. Leaves taste of garlic and are edible.

Ellen Nibali

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