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Tree leaves still clinging, more Autumn Blaze trouble and pesticide storage

Don Kinzler, Growing Together and Fielding Questions columnist. The Forum1 / 2
A reader asks why leaves are still on this silver maple so late into winter. Special to The Forum2 / 2

Q: The attached photo of the silver maple in our front yard was taken Dec. 17. The tree is 23 years old and has yet to drop the majority of its leaves. It normally is late to shed the leaves, but this seems quite late. Any thoughts on this? — Debbie Froeber, Fargo.

A: There’s actually a botanical term for this phenomenon: It’s called marcescence, which means the retention of dead plant parts that are normally shed. When dead leaves cling to a tree instead of falling, it’s marcescence (pronounced mar-SESS-ents). Good term for a game of trivia.

In leafy (deciduous) trees, as autumn weather turns cooler and days become shorter, it’s a signal for cells at the point of attachment between leaves and twigs to form an “abscission layer” that eventually unglues the leaf, allowing it to fall free. Sometimes early cold weather, frosts or other interference interrupts the abscission process or kills leaves quickly before the breakaway cell layer has a chance to form, causing leaves to cling to the tree instead of dropping. If leaves don’t fall through the abscission process, when growth begins next spring the old leaves are physically pushed off by the newly expanding buds.

Some tree types, including oak, are famous for retaining dry, brown leaves well into winter. Ash trees are among the earliest to develop their breakaway abscission layer. Silver maple and its cousin boxelder tend to hold leaves longer than some species, as you mention. Something in your silver maple’s environment interfered with abscission, so your tree is experiencing marcescence.

Q: I read your article about Autumn Blaze maple. We have one in our backyard that seems to be dying at age 12, and we’re wondering what you would suggest. Should we cut it down right away in the spring and replace with a more hard-wooded maple? There are others in our neighborhood with the same problem; however, most of them were doing great until this past spring. But, as your article said, success with Autumn Blaze can vary, even between next-door neighbors! — Tracy Bieger, Perham, Minn.

A: During the past several years, questions about Autumn Blaze maple have even outpaced questions about tomato blight.

Autumn Blaze maple, and most shade tree-sized maple species and hybrids that develop red and orange autumn color, are better adapted to areas that were once covered with native forests. From the natural forested zone in Minnesota eastward, colorful maples have a higher success rate. From the soil zone of native grassland origin and westward, such maples struggle as though out of place, with yellowing iron chlorosis and branch dieback common.

Autumn Blaze maple is considered a roll of the dice for parts of western Minnesota and much of North Dakota. Amur and Tatarian maples, smaller in stature than Autumn Blaze, are brilliantly colored low-headed screening or feature trees that are well adapted to areas where Autumn Blaze struggles. For a full-sized shade tree with bright red-orange autumn color every bit as beautiful as Autumn Blaze, but well adapted to all regional soils, choose Autumn Splendor Buckeye, Prairie Torch Buckeye or LavaBurst Buckeye, the latter two being North Dakota State University introductions.

Q: I have several containers of various weed killers and insecticides. How long will they last if I store them from year to year? I know they’re supposed to be kept above freezing. — Dan H., Fargo.

A: This is a common question since many home gardeners might use only small quantities of chemicals each season. Cornell University conducted a study in which all pesticide companies contacted recommended not storing pesticides longer than two years, and store below 100 degrees and above 40 degrees. Don’t store weed killers close to other materials such as wettable powders, dust formulations or granular products.

Some common weed killers are highly volatile substances and can contaminate insecticides, fungicides and fertilizers, especially when confined in close quarters. Store wettable powders, dusts and granular products in a cool, dry place. Always store garden chemicals in the original containers with labels attached.

If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at kinzlerd@casscountynd.gov or call 701-241-5707. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.

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