Common Soybeans Diseases Symptoms And Treatment, 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.
FUNGICIDAL SEED TREATMENT (Common Soybeans Diseases Symptoms)
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.
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/).
Soybean Rust (Common Soybeans Diseases Symptoms)
Soybean rust is potentially one of the most significant diseases of soybean. It can spread quickly and cause leaf spots and defoliation of soybean plants. Under favorable conditions, the pathogen can cause yield losses greater than 50%. Soybean rust was first found in the continental United States in the South in 2004. Since then, the disease has spread northward each growing season and has been found at low levels in the upper Midwest.
Symptoms begin on leaves in the lower plant canopy. Tan or reddish-brown lesions (spots) develop first on the underside of leaves. Small pustules (blisters) develop in the lesions, which break open and release masses of tan spores. The lesions and pustules, which can be seen with a 20X hand lens, may also appear on pods and stems. Early symptoms of soybean rust (before pustules develop) are difficult to distinguish from other common leaf diseases on soybean.
Conditions and Timing that Favor Disease:
Soybean rust can occur at all stages of soybean development, but is most common in or after the plants begin flowering and pods start developing in the middle of the growing season. Plants are most susceptible during reproductive stages. Extended periods of wet weather, moderate temperatures (59°F to 85°F), and high humidity (over 75%) favor disease development.
Two species of rust fungi cause soybean rust – Phakopsora pachyrhizi (aggressive Asian pathogen) and P. meibomiae (mild pathogen). Only P. pachyrhizi causes significant yield losses. Both fungi cause the same symptoms and can only be distinguished with specialized laboratory tests. P. meibomiae has not yet been found in the continental U.S. These fungi are obligate pathogens that survive only on green, living host plant tissue and are readily dispersed long distances by wind. The fungus survives winter on living plant tissue in the southern states and Mexico. Spores must be transported northward each growing season from areas in the south.
Disease Management: (Common Soybeans Diseases Symptoms)
Scout the lower canopy of fields weekly, especially during wet weather after soybeans begin to flower. Soybean rust must be diagnosed at an early stage to be successfully managed. Cultural practices have had little effect on the disease. Soybean rust must be managed with the judicious use of fungicides applied properly and at the correct time. Soybean varieties that are resistant to soybean rust are in development.