A22-L«ncaster Farming, Saturday, May 11,1985 “Damping off w in soybeans Seedling diseases reduce soybean stands early in the season, especially under wet conditions. Commonly referred to as “dam pmg-off,” these diseases often place soybean growers in the agonizing position of making costly replant decisions. Pythium and Phytophthora are probably the most devastating and widespread disease organisms that cause damping-off in soybeans. Rhizoctonia and Fusanum root rots also cause problems. All of these diseases are caused by soil-borne fungi that persist in the soil indefinitely. Although more commonly associated with heavy soils and poor drainage, these diseases can occur wherever soils remain water-saturated for several days. Pythium is favored by cool conditions and can kill soybean plants any time from planting to mid-season. Symptoms vary depending on the specific species of the fungus causing the infection. Seeds which become infected often rot and fail to germinate. TOe disease causes seedling cotyledon lesions, roots to rot and blocks main stem development. There are no resistant varieties to this disease. Unlike Pythium, Phytophthora is favored by warm temperatures and can kill soybean plants at any state of development. Symptoms of both diseases are similar. Phytophthora spreads through free soil water and is most severe in saturated soils. Several different races of Phytophthora have been iden tified. Fortunately, varieties are available that have race-specific resistance and field tolerance. USDA researcher develops test to detect pesticide residues WASHINGTON - Minute pesticide residues can be rapidly detected in the soil by a simple assay patterned after a human or animal’s immune system, a U.S. Department of Agriculture researcher said. The test can detect residues even though the pesticides have un dergone chemical changes that obscure their identity. “We are using a new, simplified test to identify pesticides that are altered by bacteria, light and other agents in the soil,” said USDA’s Bhon D. Dunbar, who developed the assay. “We expect the test will increase the speed and accuracy of discovering soil residues that could be an environmental concern.” Dunbar, a research agronomist {««• USDA’s Agricultural Research ■said the technique for pesticide assays could be likened to medical tests that rely on an tibodies to signal the presence of a foreign object in humans and animals. A defense is built up as the body reacts to the foreign object and produces antibodies to attack it. In the assay a pesticide is the foreign object, causing antibodies to form in rabbit serum, said Dunbar at the agency’s Central Great Plains Research Station, Akron, Colo. Warren C. Shaw, the USDA agency’s research leader for agricultural chemcials technology, said the assay “could have potentially far-reaching im plications for government and private organizations that monitor pesticides. Agencies and laboratories will be able to distinguish and measure closely Rhizoctonia produces reddish brown lesions on the roots and lower stem below the soil line. The lesions may develop into a sunken, reddish-brown canker Infected roots and stems usually remain firm and dry. Fusanum causes dark brown to black lesions on the roots and lower stem. These symptoms are often confused with those of Rhizoctonia. When the infection is severe, seedling emergence is poor. Seedlings that do emerge are often stunted and weak. The root system may be completely destroyed. When weather conditions favor the development of these diseases, a grower can do little other than wait to see if replanting will be required. However, growers can reduce the risk of replanting. Planting high quality seed into warm, well-drained soil is the first step in avoiding costly replant situations. Using bin-run seed that has not been adequately tested is risky. Fungicide seed treatments offer temporary protection from diseases during the critical seedling state. These seed treat ments are most effective in years when weather conditions favor disease development, when used in combination with resistant varieties, or when planting early in cold soil. However, fungicides do not make susceptible varieties resistant to disease. Variety selection is also im portant. Resistant or tolerant varieties may yield slightly less than susceptible ones in the ab sence of disease but are probably a better choice for fields where the risk of disease is high. related pesticides. That means monitoring can be rapid and ex temely precise.” Dunbar said the assay was first developed to detect residues at parts per trillion of atrazine, a herbicide applied to the soil to kill weeds. He said he expects private industry will develop simple test kits based on the assay. “We were able to run 100 atrazine assays in eight hours, which is much faster than using current analytical methods,” he said. If the new technique were automated, he said, at least two thousand assays a day could be done. “We are adapting the assay to detect a dozen other widely used herbicides and insecticides at parts per trillion,” he said. Current testing is done mainly at parts per billion or million. Dunbar obtained the antibodies hy first attaching atrazine moletuios to protein molecules. He used the protein molecules because they are large enough for a rabbit’s- immune system to recognize as a foreign object, while atrazine molecules alone are too small. He then injected the paired molecules into rabbits. The rabbits are not harmed by the process. “We closely monitored the rabbits,” he said. “Their immune systems recognized the molecules as a foreign substance and started producing antibodies in the blood.” He said tests showed the blood earned antibodies specifically targeted against atrazine. “We have used the antibodies suc cessfully for precise identification of how much atrazine is present in a pesticide sample,” he said. MILK BBS I I ■SST '• t > * 29H3815 Giltex-B MILKMASTER - Twin VG-87 USDAI-85 RPT9B% PD+ll4s +B46M +.03% +36F +lO2 CV$ +I9PRO.IB HFAI-85 RPT96% .08 PDT +472 TPI CAR JAY VER ELVIRA MILKMASTER has stood the test of time. At 98% repeatability this Glendell X King Pin bull has proved he can sire lots of milk from very shapely udders. 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