Garden Q&A: How do I deal with tent caterpillars?

Q:  My cherry tree had tent caterpillars on it last year. When might they come back this year, and how do I get rid of them?

A:  Insect development depends on temperature trends, and Central Maryland probably hasn’t reached the warmth threshold yet for tent caterpillar egg hatch.

This native moth spends the winter as a black, firm, foam-like egg mass on twigs. The average date of Eastern Tent Caterpillar emergence has usually been around early May. However, unusually warm weather might push that ahead into mid-April, at least based on how this year is going. Indeed, recent years have documented tent caterpillar eggs hatching in mid-April. Even late March hatching for locations like Salisbury is not unheard of. To complicate things a bit, a staggered emergence has been observed in some years, meaning that egg masses in the same general area may not hatch all at once.

This insect is relatively easy to manage, and there is only one generation per year. Even if you can’t take action in time or don’t want to interfere, their leaf chewing may appear drastic, but rarely causes serious harm to the tree. If a tree struggles to recover from caterpillar browsing, another issue is probably responsible.

Intervention would involve finding and clipping off the egg masses before they hatch, or tearing open the silken caterpillar nests later in May to expose the larvae to predators. Songbirds and several kinds of wasps will eagerly eat them for you (and those wasps will leave you alone). Some lower-toxicity pesticide options exist, but their use should not be necessary and could still risk harming pollinators and other organisms.

Q:  I tried a cover crop over my veggie garden beds for the first time this winter. They seem to be working well, but I’ll be ready to plant soon. How do I get the cover crop out of the way?

A:  You can “terminate” a cover crop by mowing it down as low as you can go (around mid-April in Central Maryland), and then covering the stubble with a light-blocking tarp for about 2 to 3 weeks. This will starve any plants trying to regrow because it denies them light for photosynthesis. The debris that’s left from the mowing can be left in place as an organic mulch (it will break down on its own as we move into the growing season) or it can be removed to compost elsewhere.

A few cover crop species, like oats and daikon radish (used for their compaction-busting taproots), usually winter-kill on their own; that is, they don’t survive winter temperatures, so most of the work of getting a planting bed ready for spring is done for you.

This year, temperatures overall have been mild enough that these cover crop radishes were faring well even into February. It’s not unheard of for daikon to power through winter here in Maryland, but rest assured, eventually, the plants will bolt (come into flower) and die on their own, so you won’t have to deal with them for too much longer. They also aren’t very tolerant of mowing, so that’s another technique to weaken the plants so they die out prior to planting your spring crops.

Our Cover Crops for Gardens web page includes more information, including a couple of video demonstrations for terminating cover crops with a tarp or mower.

University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.