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Can Compost Teas Help Flowers Battle Blight?

By Marcia Wood
May 24, 2005

Flowers and saplings may find tea refreshing.

Compost tea, that is.

These teas are made from compost "brewed" for at least 24 hours with all-natural ingredients that boost growth of beneficial microbes living in the compost. Compost teas may prove helpful in protecting wholesale and retail nursery plants like rhododendrons, azaleas, viburnums and oak saplings from what's known as ramorum blight, also called ramorum die-back or sudden oak death. That's according to Agricultural Research Service (ARS) plant pathologist Robert G. Linderman at Corvallis, Ore.

The funguslike organism, Phytophthora ramorum, which causes these diseases, has been found in at least 20 states. To prevent spread of P. ramorum, more than one-half million otherwise-ready-to-sell plants have had to be destroyed.

Some organic growers and home gardeners already apply compost teas by either spraying them on foliage or drenching plant roots. And although reputed to enhance plant growth and fend off disease, compost teas have not yet been widely investigated by scientists. So Linderman and co-investigators are studying compost teas as one of several materials that might provide an effective, affordable, Earth-friendly alternative to chemical pesticides for controlling P. ramorum.

In a preliminary experiment at the Horticultural Crops Research Laboratory, where Linderman is based, he and colleagues treated rhododendron leaves indoors with a helpful bacterium, Paenibacillus polymyxa, taken from compost. The researchers then inoculated the leaves with the ramorum organism. The scientists found that P. polymyxa did not protect the foliage, but they plan to test it again--and other potentially protective microbes--using slightly different procedures.

Discoveries by ARS scientists at Corvallis and their colleagues at other ARS labs on both coasts will be of benefit not only to the horticultural crops industry--the fastest growing sector of American agriculture--but also to home gardeners, who have made this pastime America's favorite hobby.

ARS is the U.S. Department of Agriculture's chief scientific research agency.