Birdseed May Make Your Plants Sick

July 16, 2002

COLUMBUS, Ohio - What homeowners feed wild birds may not be very good for their plants and vegetable garden.

Ohio State University plant pathologists have found that sunflower seeds, promoted as the top choice of wild bird feed, may harbor a fungal pathogen that causes Sclerotinia stem rot in a wide range of native plants, herbaceous perennials, annual bedding plants, vegetables and woody ornamentals.

In a study, published in HortScience, the researchers analyzed 10 bags of various brands of commercial sunflower seeds purchased throughout Columbus, Ohio, and found that half of them contained resting structures of the fungus -all of which were 100 percent viable.

"Nearly 2 percent of the contents of one bag was Sclerotinia resting structures. That may not sound like a lot, but when you use up a bag of sunflower seeds every three weeks for a year and each bag contains 1.7 percent of fungal spores, you're introducing a lot of Sclerotinia in your garden," said Steve Nameth, an Ohio State plant pathologist and one of the researchers of the study. "If you don't have problems with this disease in your garden, then it's not an issue. But if you do have problems, then this could be a source."

Sclerotinia stem rot, also known as cottony rot because it produces a distinctive cottony structure at the base of the plant's stem, is a major disease of sunflowers. The fungal pathogen replaces the seeds of the sunflower with resting spores, which slip through processing cracks and are inadvertently bagged in commercial wild bird feed as sunflower seeds.

"Commercial birdseed production is not an elaborate process," said Nameth. "If it was, you wouldn't be able to drop a few bucks at the local department store for a bag." Lack of attention to detail in processing, however, may cost homeowners that picture perfect plant or vegetable garden.

Sclerotinia stem rot has a host range of over 50 common ornamentals, a variety of vegetables including garden beans, lettuce and cucurbits, and even field crops like soybeans, wheat and alfalfa. The disease, which causes the plant to wilt and eventually die, can be spread two ways: either direct contact with the plant stem or wind-borne spores which can then land on a host and infect it.

"That is why finding Sclerotinia in commercial birdseed is such a concern," said Nameth. "Those spores can sit dormant for five or six years and once they come into contact with a host, they germinate like seed, attack the plant and produce a rot."

Nameth said homeowners and garden lovers can take some precautionary measures against spreading the disease, including switching to a different birdseed brand if they are experiencing problems with the brand they are using, and practicing good sanitation.

"Keep the area around birdfeeders clean. Many people pick up the hulls of sunflower seeds and use them in mulch," said Nameth. "You really don't want to do that because all you're doing is inoculating the rest of your garden with the disease."

Nameth said to also keep a sharp eye on the feeding behavior of birds that visit the birdfeeder. "The resting spores may look similar and be the same size as sunflower seeds, but the birds won't eat them."

Author(s): 
Candace Pollock
Source(s): 
Steve Nameth