Q. My hemlock has balls of white lining the stem underneath its needles. Do you know whether that’s the dangerous blight that is destroying hemlocks?
DONNA SWANSON, Milton
A. Those rows of waxy white lining the underside of the stems are telling you that your tree is hosting an invasive pest from Japan called the woolly adelgid. This aphid-like insect kills hemlocks in three to 10 years if left untreated, so you need to call an arborist immediately. The arborist should also check for another potentially deadly sucking insect from Japan on the underside of the needles: the elongate hemlock scale. If either or both insects are present, the arborist can apply a chemical systemic treatment to poison them anytime during the growing season or spray with an organic or petroleum oil to smother them, preferably in May. Expect to pay $100 to $200 a year indefinitely for annual treatment to keep your hemlock alive once it’s been infected, said Todd Caswell, a Massachusetts-certified arborist for Natural Tree & Lawn Care in Avon. (Biological-control research for adelgid has been less promising than hoped so far.) If your hemlock has already lost half of its needles, an arborist probably would recommend removing it.
Always keep trees watered during droughts if you can and avoid using fast-release nitrogen fertilizers, which end up feeding the pests more than the trees. Many of our native trees, including green and white ash and American elm, are being killed off by pests accidentally imported from Asia that they have no defenses against. So what is happening to the hemlock is far from unique. It is now vanishing from woodlands where it has been ecologically critical for shading fish-filled streams. But Abraham Monahan, a certified arborist for Bartlett Tree Experts in Hanover, won’t give up on hemlocks: “I still plant them because maintaining them is not insurmountable, and they fill a need in the landscape for a fast evergreen screen that tolerates shade. And they’re graceful.’’
Q. Do you know the date and theme of this year’s flower show?
SUE GIEBUTOWSKI, Waltham
A. Boston’s traditional kiss-off to winter, the Boston Flower & Garden Show, runs March 22-26 at Seaport World Trade Center. This year’s theme is “Superheroes of the Garden,’’ a takeoff on Comic-Con. There will be garden, photography, and botanical art displays, as well as arrangements by professionals and amateurs. Horticultural experts will speak on topics ranging from seed starting to beekeeping. Tickets are $20 for adults, $17 for seniors, and $10 for children ages 6-17. (It’s $15 after 5 p.m.) For more information, go to www.bostonflowershow.com or call 781-237-5533.
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