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IRON DEFICIENCY CHLOROSIS
Iron Deficiency Chlorosis (IDC) is often expressed as a yellowing of the first trifoliate leaves two to five weeks after planting. Problem fields are found in parts of central to north central Iowa, Minnesota, North Dakota and Nebraska on soils with a pH above 7.5. Other soil factors may significantly accentuate the expression of IDC such as high calcium carbonate equivalents (CCE) and soluble salt concentrations (EC). Soybean Cyst Nematode infestation can accentuate IDC symptoms as well.
Control: Management starts with variety selection and NuTech Seed has several outstanding options for IDC tolerance.
Higher seeding rates (12+ seeds/ft in 30” rows) can reduce IDC symptoms and improving drainage followed by soil amendments
of gypsum and/or sulphur and Iron chelate applied to the young plants at the appropriate stage can all reduce symptoms.
PHYTOPHTHORA ROOT ROT
Phytophthora Root Rot (PRR) is a fungus that can infect plants at any stage of growth and either kill plants or significantly reduce productivity. The disease can be active in cool temperatures but is generally most active in warm conditions with high soil moisture. Although PRR is most frequently associated with fields having poor internal drainage, it can also occur in normally well-drained fields saturated for 10-14 days due to excessive precipitation or irrigation. Symptoms include wilting and yellowing of the upper leaves and a dark brown discoloration that moves up the stem, both externally and internally. The PRR fungus survives and overwinters in soil or buried crop debris.
Control: Fields with a known history of PRR require a soybean with a specific gene for resistance, preferably Rps1c or Rps1k
and/or NuTech Smartcote™ Extra seed treatment. Some soybeans can also show considerable tolerance to Phytophthora.
BROWN STEM ROT
Brown Stem Rot (BSR) is likely to be the most severe in fields that have had optimal moisture in the early vegetative stage and then dry conditions during reproduction. Symptoms are expressed as brown discolorations of the inner stem between nodes, or as a late season leaf symptom consisting of brown interveinal necrosis. Look for unfilled, fully developed pods at harvest. Recent research work indicates that an inverse relationship exists between BSR and soil pH. The data collected to date indicates that the incidents of BSR tend to be significantly reduced in high pH soils and increased in low pH soils.
Control: Resistant soybeans or soybeans with considerable tolerance.
Charcoal rot is a root disease caused by a soil borne fungus that attacks young plants when their growth is retarded by unfavorable weather conditions – most normally dry soil conditions. Typical signs of charcoal rot appear after midsummer when hot dry weather slows plant growth and leaves turn yellow and wilt but remain attached to the plant. The best diagnostic symptom is found when the epidermis is peeled away from the stem where numerous small, black sclerotia give infected tissue a grayish-black color resembling a sprinkling of finely powdered charcoal – hence the name charcoal rot. The disease has been an endemic problem in southern soybean growing areas where summers are dry but can also be a problem in the central parts of the Midwest especially Kansas, Nebraska and parts of Missouri. Charcoal rot can be easily misidentified as BSR or SDS.
Control: Any cultural practice that reduces moisture stress helps control the disease. Reduced planting rates and good weed management can help control. The best control is using soybeans with tolerance to the disease.
There are many soil borne pathogens that can cause damping off of soybean seedlings. Pythium is the most common fungus responsible for damping off in cold wet soils and will be the common cause for damping off of soybeans planted in April and early May. As soils warm up, Phytophthora fungus can become a common damping off pathogen, usually in late May and early June. Both pathogens are most damaging in soils that stay saturated for a number of days and will cause the seedling to fall over and the lower stem and roots will be soft and rotted.
Control: Smartcote™ Extra seed treatment provide excellent protection against damping off. Resistance to Phytophthora Root Rot can also be helpful. Always use treated seed to replant into soils where damping off has occurred.
SUDDEN DEATH SYNDROME
Sudden Death Syndrome (SDS) is a fungal disease common to cool, moist growing seasons and has visual symptoms that begin with yellowish lesions forming on upper leaves in interveinal areas. The veins remain green, the lesions spread and eventually the entire interveinal surface of the leaf turns gray-brown. The disease infects the plant early in the soybean development and infection is increased by good moisture and cool temperatures later in the growing season. Varieties differ in tolerance and the disease is often associated with Soybean Cyst Nematode infested soils. As a rule, the disease is more prevalent in Iowa, Illinois, Indiana and Ohio, but has been spreading the last few years into Nebraska, Kansas, and Missouri. Soybean plants killed by SDS will have often have petioles still attached at harvest maturity to assist in disease identification.
Control: Avoid early planting dates, especially in fields with a significant history of SDS. Variety selection is important as there are varietal differences in SDS tolerance. Controlling SCN populations and maintaining fertility and good drainage with crop rotation is important as SDS yield losses are most severe in continuous soybeans.
White mold thrives in moist, humid and cool conditions. Significant yield losses can occur in soybean monoculture or short rotations of soybeans with other crops susceptible to the disease. White mold infestation occurs during the flowering period in late July and August if cool, moist weather is present. Infected plants will develop white, cottony fungal growth on the plant stem. A sudden yellowing or wilting is usually the first symptom. Leaves of infected plants turn brown, dry and often cling to the dead stem.
Control: Excess lodging, narrow rows and thick canopies reduce air flow and increase the risk of white mold development. NuTech soybeans are rated for white mold tolerance and several soybeans have shown reduced infection of the fungus.