Dr. Paul's Research Perspectives
Using composts for disease suppression
Two recent studies document specific effects for limiting plant diseases in strawberries and cucumbers, while a third finds that composting can kill E. coli

By Paul Hepperly, Rita Seidel, and Dave Wilson

Editors' note:
As New Farm Research and Training Manager at The Rodale Institute, Dr. Paul Hepperly has been a regular contributor to NewFarm.org for some time, providing research updates, op-ed pieces, and white papers on topics like carbon sequestration in organic farming systems.

None of those venues do full justice to the range of Paul's experience, however. Paul grew up on a family farm in Illinois and holds a Ph.D. in plant pathology, an M.S. in agronomy and a B.S. in psychology from the University of Illinois at Champaign-Urbana. He has worked for the USDA Agricultural Research Service, in academia, and for a number of private seed companies, including Asgrow, Pioneer, and DeKalb. He has overseen research in Hawaii, Iowa, Puerto Rico, and Chile, and investigated such diverse crops as soybeans, corn, sorghum, sunflowers, ginger, and papaya. He has witnessed the move toward biotech among the traditional plant breeding community and the move toward organics among new wave of upcoming young farmers. Beford coming to the Rodale Institute Paul worked with hill farmers in India to help them overcome problems with ginger root rot in collaboration with Winrock International.

Now we've decided to give Paul his own column, in which he can report on agricultural research from around the world and reflect on its relevance to The Rodale Institute's research program and to the progress of sustainable agriculture more generally in light of his own broad perspective. Enjoy.

March 11, 2005: Lately there have been increased efforts to replace soil fumigants with more natural methods of controlling root pathogens, especially on high value crops. In the recent past, the soil fumigant methyl bromide has been extensively used by conventional growers to eliminate fungi, nematodes and weeds in fields dedicated to valuable crops such as strawberries and tomatoes. Because of the role of bromine in depleting ozone in the stratosphere, however, this product is gradually being withdrawn from the marketplace. With its removal, the need to find alternative control methods has become increasingly urgent.

Many researchers are exploring the possibility of using composts to improve plant and soil health and to eliminate the need for soil fumigants. Investigators believe that composts can contribute to the creation of a disease suppressive soil environment in which pathogens are kept in check through natural biological mechanisms.

Pat Milner of the USDA Agricultural Research Service recently reported on the use of composts for strawberry root disease suppression. Milner's team compared the use of poultry and dairy manure composts at two sites, with either red stele or black root rot as the principal limiting strawberry disease. They found that at an amendment rate of just 5 percent amendment, poultry manure compost achieved an 80 percent suppression of red stele in fields located in Beltsville, Maryland. However, no positive compost effects were noted for black root rot in strawberries at the study's Germantown location. The team also found that 20 percent compost amendment rates were associated with elevated soluble salt levels.

In studies in British Colombia, Kannangara and associates found that compost applications provided effective control of Fusarium oxysporum f. sp. radicis cucumerinum, the fungal agent for a severe root and stem canker disease in greenhouse cucumbers. One bacterial strain isolated from a horse manure compost showed a 40 percent control of the pathogen in laboratory tests.

Kannangara's group also demonstrated that the horse compost contained elevated levels of a range of micronutrients compared to standard cucumber fertilizer product. The chlorophyll content of the cucumbers was improved significantly when plants were fed with compost rather than the fertilizer recommendation.

Finally, from Idaho, Hess and collaborators have reported on the heat inactivation of E. coli. Certain strains of E. coli have been implicated in outbreaks of gastrointestinal illness affecting dozens of people. Hess's team found that composting was effective in eliminating these pathogens after a total of 300 compost degree days, even when laboratory contaminant cultures were used. Laboratory cultures were harder to kill than wild cultures.

All of these studies suggest that while compost is not a universal solution for pest and disease problems, it can be a useful tool in promoting good plant nutrition and health. The effective use of compost continues to be both an art and science, with many positive attributes when used intelligently in targeted situations.

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