Overwatering Can Mean Disease

Despite last year’s drought, the most commonly diagnosed plant disease in Georgia was caused by excess water, according to University of Georgia experts.

“Out of all the samples of diseased plants we got from homeowners, nurseries, landscapers and greenhouses, root rot was the problem more than 40 percent of the time,” explained Alfredo Martinez, UGA plant pathologist. “We saw this on a full spectrum of plants, including roses, marigolds, verbenas, hollies, box woods, azaleas and rhododendrons.”

And the symptoms – known as root rot – are not exclusive to Georgia. The condition has also affected other areas of the country.

The problem with root rot is that the symptoms are confusing. “People see plants that are wilted and yellowing, with stunted growth, and they think the problem is lack of water,” he said. “So they water more.”

CAUSES ROOT ROT. Unfortunately, the causes of root rot – the fungi pythium and rhizoctonia – are very aggressive pathogens that love wet soil, Martinez noted.

“If you have root rot disease, it’s primarily a water problem,” he observed. “Chances re, either the plant has been watered too much or soil drainage is poor.”

Martinez recommends the following test to determine how well your soil drains:
Dig a hole a foot or so deep and few inches 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 that, you need to add sand or some other amendment.

SOIL SAMPLES. Take soil samples to the county extension to determine what amendments, if any, would be helpful and what sort of fertilizer would help.

“It is much easier to improve the characteristics of the soil than to treat disease that has set in,” Martinez noted.

Don't overwatering. One good watering each week is enough for most plants.

“Avoid light watering that gets the top layer of the soil wet but doesn’t penetrate the 2 to 3 inches plants really need,” he stated. “Often people overwater simply out of habit or because the top layer of soil is dry.”

It is important to check the soil from time to time to see how well it’s draining and whether plants are getting moisture. To do that, dig about 6 inches down to see how much moisture the soil contains.

DIG AROUND ROOTS. Don’t dig in the root systems of plants. “Dig around them, but make sure you get down below the root zone – about 6 inches, in most cases,” Martinez maintained. “If it’s dry and powdery that far down, 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 a landscape. Contaminated soil is another way the pathogen can be introduced.

THE TREATMENT. If root rot is diagnosed, fungicides on the market can reduce or alleviate the problem, Martinez noted.

However, the best thing to do is correct the real problem: overly wet soil. After all, the root of the problem, he said, is the roots.

The author is a science writer for the University of Georgia College of Agricultural and Environmental Sciences.