Green Scene

Joel M. Lerner's Green Scene: Springtime Advice on Spraying, Pruning and Critters

Established peonies should not be harmed by pre-emergent crabgrass killer if it is properly applied.
Established peonies should not be harmed by pre-emergent crabgrass killer if it is properly applied. (By Sandra Leavitt Lerner For The Washington Post)

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By Joel M. Lerner
Saturday, April 25, 2009

It's time for more spring questions.

Q: I live in Prince George's County. There are many Bradford pears that have been planted here and just finished blooming. Growing wild along the highways and roads is another small, white blooming tree. Is there another type of pear; are they crabapples? The blossom looks like a fruit tree. -- Barbara Putney

A: You might have seen flowering pears. Those in the wild probably aren't Bradfords, but could be seed sports from original testing since they were researched and selected in Prince George's County at the Department of Agriculture's Plant Introduction Station in Glenn Dale. Serviceberries, flowering cherries and crabapples flowered white about the same time as pears this year. They are good possibilities for the trees you saw. All four are fruit trees and can be ornamental. Their flowers look similar, and the more sun, the more flowers. Clip a small branch with leaves and bark and take it to your county Cooperative Extension Service or your local garden center for identification.

We had a lawn service spray our lawn with fertilizer and pre-emergent herbicide this spring. Three days later, my peonies were lying flat on the ground. We were assured that the chemicals would not hurt those plants. At the first sign of wilting, I washed off the plants. Will this kill only the leaves or has it gone to the roots? Some of my plants were 35-plus years old. I don't know what chemicals were used. Is there anything I can do? -- Sey Jones

There is no evidence that pre-emergent herbicides will kill actively growing perennials such as peonies. The new growth that was emerging should recover. The only ill effect from fertilizer and pre-emergent crabgrass killer is that it will also keep ornamental grass seed from germinating. If it was applied too heavily or not according to labeled directions, the fertilizer could burn new growth or stress the peonies. In clean beds, full sun and well-drained soil, established peonies should put on new shoots and perform fine as the growing season progresses.

I have a grape vine on an arbor that is producing grapes with root rot. Is there a safe, organic spray that I can use to prevent this? How should the spray be applied and at what intervals? -- Jacqueline Holland

If brown to black spots are forming on the fruit, I assume you are asking about black rot (Guignardia bidwellii). It is the most devastating and prevalent disease affecting grapes in this area because of heat and humidity. Organic controls recommended for black rot are lime sulfur or copper fungicides. They must be applied as growth begins in spring -- at about a half-inch shoot. Once the brown spots begin to form on the grapes, it is too late to spray. Providing proper cultural conditions for the vines is a necessary adjunct to using fungicides. They must have excellent drainage and air circulation so foliage dries quickly after rain and morning dew. Head back the inside shoots to short spurs so the plant stays open. Clean up all signs of the disease, including brown leaves and stems, brown grapes, and mummies of grapes that have dried like raisins and fallen to the ground or hang dead in bunches on the vine. Meticulous prophylactic steps, supported by an organic fungicide used according to labeled instructions, is considered to be the most effective regimen for control.

We had an infestation of elder bugs about 15 years ago. They disappeared until this winter. From December on, we noticed them congregating in masses outside our home and in groups of three or four indoors. They are almost completely gone, although we still see an occasional one in our home. There is an elder tree nearby. How can we keep them away and completely get rid of those in the house? -- Tom Turqman

Boxelder bugs are among the most bothersome, least harmful pests I know. Some years they are heavy and other times light. Peak seasons are late winter and fall. They are scavengers that clean up the environment, eating decaying material. They climb into trees and search for food, descending at night to find warm areas, such as mulch, furrows of bark on tree trunks or warm walls. The problem is when they occur in pest proportions, covering the side of your house and getting inside. They are related to a family of bugs called stinkbugs because they exude an unpleasant odor when startled. Catch them in a container with a little dish soap on the bottom. Use a commercial insecticidal soap in a hose end sprayer to kill them. They are not enough of a pest to use a barrier treatment of a stronger insecticide.

The caption under a photo with your column said, "Give hellebores sun." The text in the column said "give them some shade." Which is accurate? -- William Pine

The body of the text is correct. Hellebores are exceptionally shade-tolerant evergreen perennials. They are also deer resistant. You need only to cut dead foliage that occurs in winter.

How do I trim Hitchcock azaleas back about two feet? Will trimming destroy next year's blooms if I do it immediately after they bloom this year? -- Sandra Gray

Martha Hitchcocks are Glenn Dale hybrids that can grow quite large. If yours are full and green all the way to the base, selectively prune off two feet and the new growth will form new flower buds in time for next spring. To encourage new growth, do not prune more than one-third of the evergreen foliage after flowering. Always prune to intersecting branches or clusters of leaves. It is a vigorous growing plant, unless the deer discover it.

Can Leyland cypress be renewal pruned?

The Leyland can be topped and sheared. Prune it wider on the bottom than the top, so sun will reach the bottom branches. Beginning to top and shape them now is an excellent idea to maintain their ornamental value for as long as possible. You would cut the leader to the inside of the tree and allow the fuller outer branches to feather up to form a new point on top. Continue to prune as needed.

For the first time, our squad of squirrels is munching on the new growth of our oak tree. They're ruining the tree and making a mess on our driveway. Why are they doing this, and is there a way to keep them out of the tree? -- John Cece

This is an observation, not science, but squirrels love oak catkins -- the male flowers that produce pollen. Catkins are appearing now on oak trees. It might be the pollen that the squirrels are eating, or the buds. The branch tips they are chewing are dropping on your driveway, but it shouldn't hurt the oaks. Unfortunately, I don't believe it's possible to keep squirrels out of trees.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site, http://www.gardenlerner.com.


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