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Diseases of Soybeans

Several diseases, including Phytophthora root and stem rot, pod and stem blight, frogeye leaf spot, brown spot, downy mildew, Cercopsora leaf blight and purple seed stain, and Sclerotinia stem rot (white mold), are known to affect soybeans in New York. Little is known, however, about the incidence, severity, or yield effects of diseases in the state. Diseases generally are kept in check by the use of sound agronomic practices such as crop rotation and the selection of soybean varieties with resistance to diseases known to be a problem in the local area. Although there is little research information on which to base chemical disease control guidelines in New York, the following information on fungicides is included as a service to New York growers who may wish to apply fungicides.

DISEASE MANAGEMENT

FUNGICIDAL SEED TREATMENT
Treatment of seed with protectant fungicides, professionally applied by the seed supplier, is recommended for all soybean seed planted in New York - with the exception of organic production. Fungicide treatment is especially needed when seeds are planted into cold wet soils or where there is a field history of damping-off or Phytophthora root rot. Planting of bin-run seed is discouraged, though planter box application of fungicide can be made by the grower at the time of seeding. Remember to read and follow pesticide labels carefully.

FOLIAR FUNGICIDES
Several fungicide products are registered for use on soybeans by foliar application. The efficacy of these products for soybean disease control based on appropriate application timing and labeled rates is listed in Table 6.5.1 as a convenience for New York soybean producers. While each of the diseases listed occurs in the state, the data on the relationships between disease severity, yield loss, and economic return are not sufficient to base a recommendation for fungicide application to soybeans in New York. Good data from other parts of the United States, however, indicate that foliar fungicide application to a soybean seed crop (where environmental conditions and local disease pressure warrant it) can substantially increase seed vigor and germinability and can reduce the carryover of inoculum of seedborne diseases such as pod and stem blight and anthracnose.

MANAGEMENT OF ASIAN SOYBEAN RUST
Until recently, Asian soybean rust (ASR), caused by the fungus Phakospora pachyrhizi, was distributed only in the Eastern hemisphere (Africa, Asia, Australia), South America, and Hawaii. During the 2004 growing season, however, a virulent strain of ASR was detected in the southern U.S. and it now survives winters on kudzu vines and perhaps other host plants in frost-free areas. During the 2006 growing season, rust advanced as far north as Indiana. ASR can drastically reduce yields in areas where it commonly occurs, so monitoring for this disease and application of preventive measures, if warranted, will likely be necessary for New York soybean growers in certain future years. Crop insurance may require treatment to meet best management criteria. In some fields, no application may be the right decision. As of 2013, soybean rust has never been found in New York. Table 6.5.2 summarizes current fungicide use guidelines based on soybean growth stage and the regional risk of rust. Consult the USDA- PIPE Soybean Rust Information Site (sbr.ipmpipe.org/cgi-bin/ sbr/public.cgi) for the latest information on soybean rust detection and management. You can also consult an on-line manual on Using Foliar Fungicides to Manage Soybean Rust (oardc.osu.edu/soyrust/).

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