Sclerotinia

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 sclerotinia (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.

Pod and Stem Blight & Seed Decay

Other Information:

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.

Anthracanose

Other Information:

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.

Downy Mildew

Other Information:

Pale green to light yellow spots on the upper surface of young leaves which, may enlarge, forming bright yellow lesions of indefinite size. Older infected spots turn gray-brown. Spots on the lower leaf surface, especially in moist weather, have tufts of gray mycelium and spores easily seen with a lens. Older leaves are more resistant, but young leaves are susceptible. Pods may be infected without any symptom, and seeds are partly or completely covered by white mycelia and oospores, which are easy to see. Seed from infected pods may be smaller and have cracks in the seed coat.

Powdery Mildew

Other Information:

White powder-like patches of mycelia and conidia are seen on all above-ground plant parts. Additional symptoms develop on some susceptible varieties, such as chlorosis, green islands, rusty patches, and defoliation. Disease develops in cooler than normal years with reduced plant growth.

Bean Pod Mottle

Other Information:

A mild-yellow mottling is seen on the youngest leaves during rapid growth in cool weather. The mottle disappears as plants mature and plants may be slightly stunted, with distorted foliage, misshapen pods, and smaller seeds. The virus overwinters in legumes, clover, or alfalfa and is spread by insect feeding; especially the bean leaf beetle. Symptoms are masked by high temperatures, and are not seen after pod set.

Soybean Mosaic Virus

Other Information:

Infected plant leaves are spindly, narrower than normal, have dark green swellings along veins. Plants are stunted, petioles are short, as are the internodes. Infected pods are small, flat, have less hair, and are curved more. Seed germination may be reduced. This virus is seed-borne, can overwinter in perennial weeds, and is spread by aphid species.