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ASK THE EXPERTS

Avoid overwatering

POSTED: July 4, 2012 4:00 a.m.

As the summer heat begins to dry things out, we tend to think that more water is better. This is not always the case.

Many commonly diagnosed plant diseases in Georgia are caused by excess soil water.

Dr. Alfredo Martinez, a UGA Plant Pathologist, says: "Out of all the samples of diseased plants that we get from homeowners, nurseries, landscapers and greenhouses every year, root rot is the problem more than 40 percent of the time.

Martinez also noticed root rot on a full spectrum of plants, including roses, marigolds, verbenas, hollies, box woods, azaleas and rhododendrons.

The problem with root rot is that the symptoms are often confusing.

People see plants that are wilted and yellowing, with stunted growth, and they naturally think the problem is lack of water - so they water more.

Unfortunately, the common causes of fungal root rot - Pythium, Phytophthora and Rhizoctonia - are aggressive pathogens that thrive in relatively wet soil.

If you have root rot disease, it's primarily a water problem.

Chances are, either the plant has been watered too much or the soil drainage is poor, or both.

To find out how well your soil drains, try this test before you plant: Dig a hole a foot or so deep and about a foot wide. Fill it with water.

After the water has drained, fill the hole a second time.

The water should drain out in 24 hours or less. If it takes more than 24 hours, you need to add topsoil, organic matter or some other amendment.

Also, bring your soil to the extension office to have a soil test done to determine what type and amounts of fertilizer are needed to boost plant growth. It's much easier to improve the characteristics of the soil before planting than to treat diseases that might set in later.

One good watering each week is enough for most plants.

Do, however, avoid light watering that gets the top layer of the soil wet but doesn't penetrate the 3 to 4 inches plants really need. Deep and infrequent watering promotes deep, drought-resistant roots.

Often people overwater simply out of habit or because the top layer of soil is dry.

It's important to check the soil from time to time to see how well it is draining and whether plants are getting enough or too much moisture.

To do this, dig about 6 inches down to see how much moisture the soil contains. Don't dig into the root systems of plants, but rather dig around them. But make sure you get down below the root zone - about 6 inches, in most cases. If the soil is dry and powdery 6 inches deep, then it needs to be watered. Well-watered soil will stick together when it's pressed into a ball.

Another key to preventing root rot is to carefully check new plants before introducing them to the garden.

Contaminated soil is another way that pathogens or diseases can be introduced. Take one or two plants out of a flat of bedding plants and take a close look at the roots. Roots should be white or silvery. If they're brownish, soft or sparse, then the plant is probably infected with a root rot-causing pathogen.

Most all of the pathogens that cause disease are with our plants or in the soil all the time waiting on the proper environment to cause us problems.

If root rot is diagnosed, fungicides are on the market that, if wisely chosen, can reduce or alleviate the problem.

However, the best thing to do is to correct the real problem: Overly wet soil.

After all, the root of the problem is in the roots.

Clark MacAllister is the Dawson County extension agent. For more information, call (706) 265-2442.

 

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