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Leaves are showing signs of age

Posted: Sunday, August 23, 2009

My childhood best friend recently reached a milestone birthday; 50 years old.

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I had to call and give him a hard time about reaching the half-century mark. He let me go on for a little bit then reminded me that I wasn't far behind him.

As I get older, I seem to notice little problems more. At this time of the year, you can look at the leaves of your deciduous plants and they will have all kinds of little problems.

This year, these leaves were subjected to a cool wet spring followed by a hot, dry summer. These are not the best growing conditions for most of our plants. They have been under a lot of stress, and the leaves are beginning to show it.

When the plants get stressed, the leaves are attacked by a number of fungi and bacteria. As it gets later in the season, deciduous plants' leaves will have leafspots. Some of the plants showing leafspots now are laurels, ligustrums, camellias and dogwoods.

One of the diseases in the landscape that causes concern is called shot-hole disease. It gets its name from the circular holes in the leaves that eventually join and make larger holes. The shrubs look like they have been shot with a shotgun. Leaves appear to be eaten away by the disease, leaving a ragged appearance. As leaves are damaged, they begin to fall away, the ability of the plant to make food decreases, and the plant can become stressed.

This is more of a factor early in the season. The September infection is not as damaging to the plants as the May infection. Shot-hole disease will attack laurels, camellia, ligustrum (privets), hydrangea and ivy. Otto luyken and bay laurels are two of the plants that are most often attacked by this disease.

The shot-hole disease is a combination bacterial infection (Xanthomonas prunii ) and fungal disease (Blumeriella gaapi and/or Cercospora sp .) These pathogens can attack the plants beginning in April and will go through October. The peak time for infection is in May and September.

The best way to help plants fight this problem is to practice good sanitation.

Clean up contaminated leaves from under the plant. When diseased leaves build up under the plant, it produces a constant supply of spores that can infect the plant. These spores are spread by water, so rain or watering can splash the disease back up on the plant.

Remove the old mulch from around the plants and replace with new mulch. Also, help protect the plants by spraying them with a fungicide such as Mancozeb, Kocide, Kop-R-Spray or other recommended products containing copper at the first sign of a problem. Whenever using pesticides, always carefully read the label and directions.

One very common leaf spot on hydrangea is Cercospora leaf spot caused by the fungal pathogen Cercospora hydrangea. This fungal leaf spot can affect most hydrangeas and is generally an appearance issue for homeowners. The pathogen that causes this leaf spot will rarely kill the plant, but it can reduce plant vigor by defoliation.

This disease is usually more of a problem in low-maintenance landscape situations or when homeowners wet the leaves when irrigating their plants.

Depending on the type of hydrangea, the leaf spot symptoms may vary. The spotting of the leaves will begin at the base of the plant on older leaves and will work its way up the plant. The spots on the leaves are generally small, circular, and scattered across the leaf surface. They tend to have tan centers and dark brown or purple borders. The leaf spots can be irregular or angular shaped.

Because this disease shows up late in the summer, fungicide applications are rarely needed, because the plant has stored enough energy to come back the next year. However, if you feel that you have to spray your plants, you can use a fungicide to protect them. Some of the appropriate fungicides are Chlorothalonil, Myclobutanil, Mancozeb and Thiophanate-methyl. Begin spraying when you first see the leaf spot, and then follow the label instructions for repeat applications (usually every 10-14 days). Again, sanitation and proper watering are the best options in helping to control this problem.

Late-season leaf spots are less stressful to plants than early-season leaf spots. The leaves of deciduous plants will be falling off soon, anyway. If you have fertilized, watered and maintained your plants for the best growth, they can withstand late-season diseases.

Columbia County Extension Agent Charles Phillips can be reached at (706) 868-3413 or by e-mail at charlesp@uga.edu. The Extension Web address is www.ugaextension.com/columbia.



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