Diagnosing Plant Ailments

High fever, nausea and headaches are all signs that a person is ill. If you pay attention to the signs, your landscape plants will let you know when they're sick, too.

"Plants put out symptoms just like humans do," says Todd Hurt, a landscape specialist with the University of Georgia Center for Urban Agriculture. "You have to learn to be a landscape detective and pick up on the clues your plants are leaving you."

A former Cooperative Extension agent in Florida and Georgia, Hurt has done his share of plant detective work. He finds that most plant problems "are rarely the result of a single factor."

Ask a few questions

When diagnosing problems in your home landscape, Hurt says to ask yourself a few questions:

• Is more than one plant species damaged?
• How many plants are affected? 
• Is the damage on all the plants or is it localized? 
• When did you first notice the problem? 
• Have you recently applied a pesticide, herbicide or fertilizer?

When an insect attacks a plant, it is usually attracted to a specific plant species. "You won't see an azalea pest hop over and feed on a boxwood," he said.

Bag or bottle 'em

If you find an insect on your plant, save it in a bottle of alcohol and take it to your county Extension agent for identification. If your pest is a caterpillar, preserve the critter first.

"If your wife is willing to let you use the family stock pot, blanch the caterpillar briefly in hot water before placing it in a vial of rubbing alcohol," Hurt said. "This will preserve the color until you can get to your county agent."

Plant leaf samples should be placed in a ziplock bag and kept cool until your county agent can identify the problem, he said. “Do not add water to the bag,” Hurt said. “Extra water will cause the sample to rot.”

Root samples should be placed in a separate bag to avoid cross-contamination of soilborne diseases.

Ask first, spray later

If you think your plants have been infected by a plant disease, take a sample before you spray a fungicide.

“If you take a sample after you spray, you could actually mask the disease,” he said. “If at all possible, wait until after you confirm the problem with your county Extension office. Most plant problems can be corrected without the use of pesticides.”

Plant diseases move through a landscape progressively. "They will start in one area," Hurt said, "and gradually move to all the plants."

You can diagnose a plant problem, too, by looking at where the plant is affected. "If the entire plant is brown, you're most likely dealing with a root problem," Hurt said. "If it's just on the new growth, you know that you've discovered the problem quickly."

Don't rule out human error

Yellow leaves can show that your plant needs more water, he said. On the other hand, Hurt has seen plant leaves turn yellow as a result of human error.

"I once got a call from a man who wanted to know how to treat his plants for yellow leaves," Hurt said. "All of the plants along one side of his home had turned yellow. After looking at the plants and talking with him, I figured out his plants were actually suffering from the effects of the bleach he used to pressure-wash his house. No pesticide or herbicide was going to cure them."

If the damage is distributed evenly across your entire landscape, the cause is likely environmental, he said.

Environmental factors that affect plants also include cold or drought damage or, as in the case of the bleached plants, damage caused by humans, he said.

Another case Hurt solved involved burned leaves."It wasn't drought or lack of water," he said. "The leaves were burned by the sheets of black plastic he placed on the plants to protect them while he painted the house."

Source: Sharon Omahen, University of Georgia