Sclerotinia
 (Stem Rot)

Other Information:

Flower petals are infected and mycelium colonizes the stem and pods. Stem tissue becomes tan or white and may be covered with white Mycelium and black sclerotia (round, oblong, hard, black structures). The top of the plant dies and turns brown. This is often the first symptom observed. Stem lesions may increase lodging. Sclerotia on the stem fall to the ground and others inside the pith are released when seed is harvested. Sclerotia can be found with the seed. The fungus survives winter as a Sclerotia and can remain alive in soil for many years. Sclerotia germinate in Warm/wet spring, summer, or fall periods and release spores that are wind-borne. Soybean infection requires moisture on the flower petals, and is favored by closely-spaced plants that form a dense canopy early.

Phytophthora
(Seedling Blight Root & Stem Rot)

Other Information:

Symptoms include stand reduction, root rots, and basal stem decay. Seed rot and pre-emergence damping-off are often credited to water damage. Taproots are usually dark brown, and small feeder roots are rotted or Missing, on plants that survive the seedling phase. Stem discoloration, dark brown surface from the soil line up 6 inches, is less common on more tolerant/resistant varieties. Leaves on older plants become chlorotic, stunted and may wilt, die, turn brown, and remain attached to the plant for some time. This fungus survives as an "oospore" in infected crop debris. The oospore germinates in wet soils and releases many "zoospores" that Swim to developing soybean roots and infect. Disease and infection is favored by wet conditions and soil temperatures near 60ºF. Low, poorly drained compacted soils, or soils with high clay content, or sites that are normally well-drained but wet, increase disease severity.

Rhizoctonia
(Root Rot & Lower Stem Decay)

Other Information:

Post-emergence damage is a bigger problem than is pre-emergence death. Root symptoms are confined to lateral root decay and outer root surface damage only. A red-brown discoloration of the hypocotyl and lower stem does not extend above the soil line. Slow growing plants are damaged most, and symptoms, wilting, and death develop following warm, dry weather early in the season. This is another soil inhabitant that survives in soil as sclerotia or as "resting" mycelium in crop residue. Infection is favored by wet and cool conditions followed by warm and dry periods that stress the plant. Young plants are most susceptible, but stressed older plants may die if moisture is limited.

Brown Stem Rot

Other Information:

Root infection precedes discoloration of water conducting vessels and at midseason the vascular elements and stem pith show a reddish-brown color. The brown color develops first at the stem base and moves up, often most evident at nodes. Yield reduction increases with greater discoloration. Leaf symptoms develop later in the season. Look for wilt, interveinal browning and green tissue over the vein, leaf drying, and early leaf drop. Plants do not mature normally, and appear to be frost damaged. This fungus survives in crop debris and increased inoculum levels are reported following tolerant varieties. Cool weather leads to more stem browning and warm dry conditions increase foliar symptoms, especially during the reproductive stage.

Pod and Stem Blight & Seed Decay

Linear rows of brown to black fruiting bodies, "pycnidia," are seen on stems, but are scattered on pods. Infection of healthy plants is common, but the pycnidia are produced only on dead or dying tissue. Seeds in infected pods have a white, moldy growth, are wrinkled, smaller, and germinate poorly. Seed infection tends to be greater when warm wet or humid weather delays harvest. Plants that are killed early, or plants that are harvested late in wet or warm humid late summer, often have pycnidia present. Infected seed can produce infected plants, but most infection comes from inoculum in infested crop residue. Spores splash on plants during wet weather and infection is favored by injuries, hail, or lesions caused by other pathogens.

Anthracnose

Symptoms appear at early reproductive stages on stems, pods, and petioles. Watch for leaf rolling, petiole cankers, veinal necrosis, and early leaf drop. Stem and pods have black fruiting bodies, "acervuli," with black hairs, "setae". Seed are shriveled, moldy, and stained brown or dark. Early season infection can be from seed inoculum, while infection during flowering is mostly from infected plant residue. High plant populations and wet canopies favor disease development.

Stem Canker

Infection symptoms develop during early reproductive stages at nodes as a small red-brown lesion. Over time, the lesion expands, forming a darker brown, elongated sunken canker. Leaf tissue yellows between the veins and, with reduced water flow, death of leaves is common. At times, top growth ceases and a shepherd' s crook curl develops. Girdling and toxin production are responsible for symptoms and death. Symptoms in Minnesota often are field and seedlot specific, and may have resulted from seed contamination. However, the fungus is reported to survive on infested debris. Most soybean cultivars can be infected, but only those that are susceptible allow the disease to develop.