Q. My boxwoods have many leaves that are folded over. When I unfold them, I see this strange gray, waxy material. Is this a disease and should I be spraying something?
A. It's not a disease. Your boxwoods have psyllids. Similar to aphids, these sucking insects are light green and / inch long. They produce that fluffy, white wax that you observed. If you examine the leaves and see the nymphs, you can apply a horticultural oil or insecticidal soap spray. The winged adults usually appear in June.
Q. I have an invasive weed in my flower beds that has a thick root and comes back every year. The leaves are arrow shaped. My neighbor has sorrel planted in her herb garden that looks very similar but is not invasive. I'm confused. How do I get rid of this weed?
A. You have sheep sorrel, a different, more invasive species than your neighbor's culinary sorrel. This perennial weed spreads by seeds and rhizomes (slender underground roots). Cut and remove the flower heads before seed is formed and try to dig up as much of the root system as possible. You can also carefully spot-treat with a nonselective herbicide.
Q. I'm frustrated by the way squash plants sprawl all over my small garden. Can you stake these plants like tomatoes?
A. You can't easily stake a squash plant. Instead, try enclosing the plants with a circular fence made from a 9- to 10-foot-long piece of 3 foot wire. This will keep the plant in bounds and make harvesting easier.
THIS WEEK'S CHECKLIST
1. Avoid using broad spectrum insecticides like Sevin, because they kill a wide variety of insects, including pollinator bees and caterpillars that provide food for migratory birds and other wildlife. Use B.t., a microbial insecticide, when a pest caterpillar must be controlled.
2. Cover newly emerging bean and corn plants with floating row cover to keep birds from eating the seedlings.
3. Put tropical lilies out in backyard ponds. Most varieties require a minimum of five to six hours of sunlight each day.
Garden tips are provided by the Home and Garden Information Center of the Cooperative Extension Service of the University of Maryland. For additional information on these questions, or if you have questions of your own, call the center's hot line at 800-342-2507, or visit its Web site at www. agnr.umd.edu/users/hgic.