Rhododendron has 'winter burn'

Garden Q&A

March 16, 1997

As I was walking around my yard this past weekend, I noticed that the leaves on my rhododendrons and azaleas were brown along the edges. What could be wrong?

"Winter burn" -- marginal leaf browning that results from drying winter winds -- is probably the cause of your problem. The browning is caused by the removal of water in the leaves faster than the plant can replace the water from frozen soil. Mild cases of winter burn will not appreciably affect plant vigor. To reduce the chance of winter burn, water shrubs during dry fall months and erect protective plastic or burlap barriers 1.5 feet from the plant on the windward side of vulnerable plants.

I want to build raised beds this spring for growing vegetables but am a little concerned about using pressure-treated lumber. Are there any good alternatives? If I use the treated lumber, how can I minimize my exposure to the chemicals?

You can create a raised bed without the benefit of a wooden border. Simply mark off an area 3 to 4 feet wide and as long as you like. Remove the sod or cut it into small pieces. Dig down as far as possible, turning the soil. Use a garden fork to loosen the subsoil and mix in 4 to 5 inches of organic matter (aged horse manure, leaf compost, etc.).

Rocks, bricks and plastic "planks" can all be used to enclose a raised bed. Rough-cut oak and poplar from sawmills also make very sturdy and long-lasting borders for raised beds. If you go with the treated lumber, be sure that it is completely dry when you buy it. You can minimize any leaching of the arsenate, copper and chromium injected into the lumber by stapling plastic sheeting along the inside of the boards.

I just cut out my dead raspberry canes from last year and noticed some problems on the canes that will flower this year. Some have purple streaks and others have brown streaks and look pretty weak. What's causing these problems and what can I do about them?

Cane blight and anthracnose are two fungal diseases that cause cane stems to discolor. Spraying canes at this time with liquid lime sulfur will help control these diseases. Prune out weak and badly diseased canes and thin the remaining canes so that they are at least 6 inches apart.

You may also have cane borers in your planting. In June watch for wilting of cane tips.

This is a sign that the female cane borer is laying eggs. Prune out wilted tips at least 6 inches below the wilting.

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.

Checklist

Remove the wraps put on tree trunks to protect them from winter pests. Leaving the wraps on through spring will interfere with a tree's growth and encourage insect and disease problems.

Fertilize asparagus and rhubarb beds with 2 to 3 pounds of 10-10-10 fertilizer per 100 square feet. Or spread 4 to 5 bushels of rotted compost or horse manure over the same area.

Handle flower and vegetable seedlings by their leaves when potting up to larger containers. Handling the stem of a young plant can easily damage the plant.

Pub Date: 3/16/97

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