A NEW WAY TO CONTROL SOIL DISEASE!

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by Greg and Pat Williams

Researchers have known for years that adding organic matter can control some soilborne plant diseases. For example, Australian avocado growers have successfully limited phytophthora root rot by incorporating sizable amounts of organic materials in their orchards. Recently, though, two plant pathologists at the National Chung Hsing University in Taiwan have concocted a new soil amendment that—almost miraculously—controls numerous bacterial and fungal pathogens when added at very low rates to diseaseinfested soils.

This "S-H" amendment (named after the last initials of its originators) consists of 8.4% rice husks, 4.4% bagasse (sugar cane press residue), 4.25% oyster shell powder, 8.25% urea, 1.04% potassium nitrate, 13.16% calcium superphosphate, and 60.5% mineral ash (the ash contains approximately 44% calcium oxide, 31% silicon dioxide, 18% aluminum oxide, 1.7% magnesium oxide, and 1% ferrous oxide).

Experiments with the amendment have yielded spectacular results. Container watermelons grown in a sandy medium infested with wilt fungi were completely protected by the addition of 1% S-H by weight . . . and field watermelon trials in wiltladen soil showed that applying about 30 pounds of S-H amendment per 1,000 square feet gave excellent wilt control. In other field trials using a similar application rate, S-H significantly reduced the incidence of radish yellows (caused by Fusarium oxysporium f. sp. raphani) and mustard-cabbage yellows (caused by Fusarium oxysporium f. sp. conglutinans). The soil supplement also helped control clubroot in cruciferous plants (caused by the slime mold-like Plasmodiophora brassicae) . . . tomato bacterial wilt (caused by Pseudomonas solanacearum) . . . rhizoctonia blight of beans (caused by the fungus Rhizoctonia solani) . . . and southern blight of peppers (caused by the fungus Sclerotium rolfsii).

No doubt, several factors work together to increase S-H's effectiveness. Apparently the calcium in the amendment inhibits spore formation of Fusarium fungi, while other inorganic materials appear responsi ble for germ tube lysis (destruction) in the fungi. Some of the pathogen control may also be due to increased soil pH from the alkalinity of the amendment. What's more, populations of nonpathogenic soil fungi are often greatly increased by S-H treatments.

In short, S-H amendment has tremendous commercial potential—it's worth trying by any grower who's bothered by soilborne diseases. The Taiwanese Patent Office granted a patent for the amendment in 1984, and a fertilizer manufacturer there is already massproducing it for commercial growers. We predict that it will become available in packaged form for North American growers in the near future.

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