Q: I have a hedge of boxwoods that are looking somewhat orange-tinted and less dense than usual. What might be causing this?
Boxwood leafminer is my main suspect, and I have recently seen boxwoods looking just like you describe, which had high populations of this common insect pest.
With only one generation per year, this species of fly is in its larval (juvenile) stage inside the leaves. Since larvae feed on tissues between the upper and lower leaf layers, you need to peel the leaf apart to find them to confirm their presence. Outwardly, affected leaves will become blistered-looking and have a blotchy yellow or orange-yellow color. Leafminer damage can also cause the shrubs to shed some leaves prematurely, so the branches will have more sparse growth towards the plant’s interior than a healthy shrub would have.
Boxwood leafminer larvae are tiny orange-yellow legless maggots, only a few millimeters long, though they are readily visible if you open a leaf and examine it with a hand lens, since the rest of the leaf interior will be light green. They will pause feeding as winter approaches and overwinter in a state of suspended development, resuming more voracious feeding in early spring. Larvae pupate and transform into orange gnat-like adults by late April or early May.
Some boxwood cultivars have greater resistance to leafminer than others. When the insects are too abundant for their damage to be tolerable, prune out the infested branch tips or, as a last resort, consider using an insecticide to reduce their numbers. Keep in mind, though, that insecticide use can have unintended consequences: it might facilitate an increase in the population of boxwood spider mites; harm pollinators visiting the boxwood’s flowers; or harm insect or spider predators wandering its foliage that would be eating pests.
You can learn more about leafminer as well as other common boxwood ailments on Extension’s boxwood diagnostic web page, go.umd.edu/boxwood.
Q: Something dug into the potting mix in a container of annuals. It looks loose and disturbed in one area, though I don’t see a distinct hole. What could it be, and how do I stop it?
While we often blame insects or small mammals for holes dug in lawns and garden beds, sometimes the culprit may surprise you, especially in the looser potting mix in containers: toads.
Maryland is home to two similar-looking toad species: the American toad and the Fowler’s toad. They can burrow into soil when temperatures are high or the weather trends dry, as well as for shelter over the winter. Soil temperatures don’t get as cold as air temperatures, so their burrows are well-insulated, though potted plants could freeze more extensively because of their much smaller volume.
Toads burrowing in potted plants may be a nuisance if they push soil out of the pot or disturb the root ball of a plant in the process, but they are great garden pals to have around since they eat pest insects. Plus, who doesn’t love encountering their little grumpy-looking faces? If your pots are near a light source at night (like on a porch or deck), a toad may enjoy hunting the insects attracted to the light, then take shelter in your pots. Better to keep such lights off when you can, though, to spare harmful impacts for insects, migrating birds, and other animals.
Toads lounging unwanted in potted plants can be relocated to the garden where they can find new shelter. Before bringing them in, check any houseplants you may have summered outside. Loose potting mix on the surface may indicate that you have a visitor that you don’t want hitching a ride indoors.
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.
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