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How to prevent the disease that made these flowers ragged

"Fielding Questions" columnist Don Kinzler also hears from readers on a smart tip to scare birds away from a tree and weighs in on pruning shrubs now after a hot summer.

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A reader asks if Don knows the apparent disease affecting this phlox. Special to The Forum
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Q: A friend asked me about this apparent disease on her phlox, as shown in the photo. Do you know what it is? — Jay G.

A: Tall phlox, sometimes called garden phlox, is very susceptible to foliage diseases caused by fungi, which cause yellowing or browning of leaves. A badly affected phlox can become ragged or defoliated by midsummer.

To prevent phlox mildew and similar fungal diseases that repeatedly affect such perennials, begin early in the season while the leaves are still green and healthy. Apply an all-purpose flower or vegetable fungicide containing the active ingredient chlorothalonil. Apply every 10-14 days following all label instructions.

Fungicides are most effective as preventatives to keep foliage healthy or to stop the spread at the very earliest disease symptoms. Once leaves are blighted, spotted and yellow, those leaves will not return to normal health.

Many new phlox varieties have been developed with disease resistance as a selling point, as indicated on their description. To further decrease the chance of foliar diseases, avoid getting water on leaves and water early in the day so foliage dries before nightfall.

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A reader asks if Don knows the apparent disease affecting this phlox. Special to The Forum

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Q: Years back I found a way to scare birds from our large elm tree, under which I was forced to park my ’98 Monte Carlo. The birds loved that tee, but apparently hated my car’s paint job, sunroof and me, I guess, as they messed all over the car. Anyone with bird issues in trees couldn’t go wrong with this method. — Ryan C.

A: Ryan continues by describing the bird-scaring method. “My friend suggested I ditch the fake owl I was using, which scared nothing, and hang CDs in the tree. I drilled small holes near the edge, used good monofilament fish line and hung about 30 throughout the tree.

“The CDs spin and twitch in the slightest of breezes, and they glint and shimmer no matter the angle of light, and they last forever. I never saw another bird in that tree again. The car’s paint and my happiness were both saved.

“Unlistenable CDs are everywhere, although I probably overdid putting 30 in one tree. We lived there for another six years before moving, and the CDs were still keeping the birds away.”

Thanks, Ryan, for the interesting tip and testimonial. Birds can be a nuisance to what’s parked below, but they can also seriously damage trees. Sapsuckers and other woodpeckers can disrupt a tree’s flow of water and nutrients which can kill a tree if holes are closely spaced and plentiful. I receive many requests from tree owners seeking to halt bird damage, and I’ll pass along this suggestion.

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Q: I delayed pruning some of our shrubs because it’s been so hot. With temperatures forecast to be a little cooler, is it OK to prune now? Some of the shrubs have gotten quite large, and I’d like to cut them back by quite a bit. — Mary S.

A: Generally, most pruning of deciduous (leafy) trees and shrubs is best done in early spring after winter’s severest cold is likely past, and before they leaf out. March and early April are good pruning months.

If pruning is delayed until after leaves are produced, plants waste energy on growth that is simply pruned away and discarded. Dormant pruning conserves plant energy for a greater growth push when spring arrives.

There are certainly exceptions. Shrubs that flower in spring, like lilac and forsythia, can be pruned immediately after bloom. Dormant spring pruning would cut away their soon-to-open flower buds that were formed last summer.

Few shrubs are killed by pruning at the wrong time, but dormant pruning is still a sound recommendation for serious cutbacks. Light trimming or shaping of shrubs like spirea is fine until midsummer.

Heavy pruning after July 4 isn’t generally recommended because such pruning stimulates a flush of new growth that might not have enough time to toughen up or “harden off” before winter, increasing the chance of branch dieback. Avoiding heavy pruning this summer was especially wise because shrubs have been stressed enough from heat and drought. I would wait until early next spring for pruning projects.

If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at donald.kinzler@ndsu.edu. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.

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Don Kinzler, "Growing Together" and "Fielding Questions" columnist.

Don Kinzler column mug.jpg
Don Kinzler, "Growing Together" and "Fielding Questions" columnist.

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at donald.kinzler@ndsu.edu.
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