Ask the Gardener: Dealing with weeds, moths, and plant viruses

Ask the Expert Gardening

What to do this week: Avoid unnecessary mowing, as grass grows more slowly now. Don’t scalp your lawn. It will grow deeper roots and need less water if you keep it at 3 inches in the summer. Deadhead spent flowers throughout the summer to conserve plant energy and encourage re-blooming. Shear back or snap off individual flower heads. Prune bloomed-out rose stems back to just above a five-leaf joint. Apply an organic fertilizer such as Rose-tone once a month to roses, and water deeply at the base each rainless week, trying not to wet the leaves. Water container gardens daily in hot weather. Most other plants (including trees) need an inch of water per week, either from rain or from you. Harvest squash or peppers at any size. Harvest eggplant when they are 4 inches and still shiny. Harvest garlic when the top leaves have started to brown.

Q. I bought a new house with an existing garden. How can I tell the plants from the weeds?

P.D., Milton

A. Many weeds are annuals that will pull out with a light tug, while many garden plants are perennials with big roots that resist weeding and require a garden fork to pry out.


Q. I am seeing large buff-colored moths fluttering by each day. Are they gypsy moths? What should I do?

R. D., Canton

A. Probably. These pests are making a temporary comeback, and those insects are males looking for females. You can arrange for a certified arborist to spray your oaks, willows, roses, maples, and cherries next spring. Make sure they schedule the spraying when these plants are not in bloom, as the most common insecticides for gypsy moths, acephate and carbaryl, are toxic to bees. No need to spray dogwoods, red cedar, tulip trees, holly, mountain laurel, or catalpas, which most gypsy moths pass up.


Q. Some of my dahlias have leaves of mottled color. Is this a virus? If so, do I have to destroy them, and can I ever plant healthy dahlias in the same spot?

D.D. Newton

A. There are several kinds of plant viruses, but there’s no cure for any of them. Though viruses can stunt and distort plant growth, the biggest reason you have to pull out and destroy all infected plants is that sucking insects moving through the garden can spread it to healthy plants. Also, any plants propagated from the diseased stock will carry the virus. The common mosaic virus creates a mottled effect, with patches and streaks of yellow on otherwise green leaves.

Many common weeds and garden plants can carry a virus, including cucumbers, tomatoes, cauliflower, peonies, columbines, delphinium, iris, impatiens, asters, gaillardia, squash, and zucchini. Remove and destroy any plants with symptoms, which include paler green or yellowing patches, streaks of veining on otherwise green leaves, twisted or curled leaves, and warty or mottled fruit. Remove weeds as well. Don’t compost them. I bag them for garbage collection and carefully wash my hands and any tools that come in contact with the infection.

The virus should disappear with plant removal, but to be safe, I would wait a couple of years before planting dahlias or other susceptible plants in the same location. Think of it as crop rotation.

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