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College of Food, Agricultural, and Environmental Sciences


A Clean Greenhouse Means Healthier Plants

July 10, 2002

COLUMBUS, Ohio - The cleaner the greenhouse, the fewer the problems with insects and plant diseases.

That's the message Steve Nameth, an Ohio State University plant pathologist, is striving to drive home to horticulturists, gardeners and nursery professionals.

"I always tell people to imagine the level of cleanliness in a greenhouse as they would envision in a hospital. You want the environment as microbial-free as possible," said Nameth. "Unsanitary conditions are going to contribute to disease and insect development and their spread from one plant to another."

Nameth will discuss the importance of greenhouse sanitation at the 2002 Ohio Florists' Association Short Course on July 17 at 10 a.m. The educational event and trade show will be held from July 13-17 at the Greater Columbus Convention Center and will bring together professionals from around the country to discuss a wide variety of topics pertaining to the floriculture industry. Over 180 seminars will be presented.

Nameth said keeping a greenhouse clean and dust-free is a common-sense responsibility that more growers should follow.

"Most growers could do a better job at sanitation," said Nameth. "They have not had to pay attention to that because of the chemicals that are available to control diseases and insects. It's just easier to spray than it is to clean up, but we try to encourage growers to follow practices to avoid diseases that don't involve chemicals."

Major sanitation concerns in the greenhouse include the presence of weeds, dust, plant debris, clutter, pet plants and personnel maintenance.

Nameth said weeds are one of the biggest harbors of plant pathogens. "The more weeds in the greenhouse, the more insects, and especially diseases, that are present because of the increased humidity that weeds generate," he said.

Standing water in the greenhouse also contributes to weed development, which leads to an increase in plant diseases. "Many people don't realize it, but algae is the No. 1 weed in the greenhouse. Not only is it a hazard for people working, but it's just a humidity factory," said Nameth. "If you've got algae in your greenhouse, that tells you you've got too much humidity and, as a result, too much standing water."

Dust, debris and general clutter tend to be a magnet for insects and diseases. "Raising a cloud of dust in the greenhouse just spreads fungal spores everywhere and clutter and plant debris are just vehicles for collecting dust," said Nameth. "Growers should keep their greenhouse floors as clean as possible and throw away any debris and then empty the trash can, so that there is no trash anywhere in the greenhouse."

Even unassuming factors, like working habits or maintenance of pet plants, tend to contribute to disease development. "Employees should make sure that they are sanitizing their hands and not moving from one greenhouse to the other without doing so. Some bacteria and viruses are very infectious. All one has to do is touch or rub up against a plant and they can easily transmit the disease from one plant to another," said Nameth.

"Pet plants, or household plants, that growers overwinter in greenhouses are sources of year-round diseases and should be discarded. Growers should give their greenhouses a clean start every year," he said.

Nameth will also discuss perennial plant disease management and the latest on bacterial wilt of geranium and daylily rust under separate sessions during the short course. For more information on the 2002 OFA Short Course call (800) 737-9486 or log on to

Candace Pollock
Steve Nameth