Encyclopedia - Soybeans

Use the Search and Filter options to help select only the crops, types of disease, and timing of disease you are interested in from the list below. Only articles meeting your chosen criteria will be shown. These articles contain information and images for identification and basic management of crop diseases.

Search and Filters

Aerial Blight of Soybean

Aerial blight (also known as Rhizoctonia foliar blight and web blight) is mainly a problem in the southern U.S. where soybeans are grown in rotation with rice. First leaf symptoms appear as water-soaked, grayish green lesions that turn tan to brown at maturity. Read More

Alfalfa Mosaic of Soybean

Symptoms caused by Alfalfa mosaic virus (AMV) are patterns of bright yellow and dark green leaf tissue. Newly emerged leaves may be small with bright yellow spots and brown discoloration and plants may be stunted. Alfalfa mosaic is transmitted by more than 15 aphid species, including the soybean aphid. Alternate hosts of AMV include alfalfa, other legumes, and solanaceous... Read More

Anthracnose Stem Blight of Soybean

Anthracnose stem blight is generally a late season disease prevalent on maturing soybeans. Irregularly shaped red to dark brown blotches on stems and petioles can appear during early reproductive stages. Petiole infection can result in a shepherd's crook (curling or "hooking" of plant tissue). Near matur... Read More

Bacterial Blight of Soybean

Bacterial blight is usually one of the first foliar diseases to occur on soybean. Bacterial blight seldom causes serious yield loss. Symptoms usually begin in the upper canopy because young leaves are most susceptible. Small, angular, reddish-brown lesions are surrounded by a yellow halo. As the disease progresses, l... Read More

Bacterial Pustule of Soybean

Bacterial pustule occurs mid- to late season when temperatures are warmer. Lesions are found on outer leaves in the mid- to upper canopy. Lesions start as small, pale green specks with elevated centers and develop into large, irregularly shaped infected areas. A greenish-yellow halo surrounds each lesion. A... Read More

Bean Pod Mottle of Soybean

Foliar symptoms caused by Bean pod mottle virus (BPMV) include distorted and wrinkled leaves that have a mottled color pattern. Symptoms appear more severe on young leaves, sometimes with a raised, blistered, or distorted appearance. Symptoms are most obvious at cooler temperatures and often disappear when it is hot. Infection by BPMV decreases pod formation, reduces see... Read More

Brown Stem Rot of Soybean

Brown stem rot (BSR) is caused by the fungus Cadophora gregata. Characteristic foliar symptoms of BSR include chlorosis and necrosis between leaf veins, followed by leaf curling and leaf death. Leaf symptoms vary depending on soybean variety, fungal strain, and environmental conditions. In some instances, no foliar symptoms occur. Foliar symptoms can be similar to those o... Read More

Cercospora Leaf Blight of Soybean

Cercospora leaf blight is frequently seen but rarely causes yield loss. Foliar symptoms usually are seen at the beginning of seed set and occur in the uppermost canopy on leaves exposed to the sun. Leaves are typically only discolored on the upper surface with symptoms ranging from light purple, pinpoint sp... Read More

Charcoal Rot of Soybean

Initial symptoms of charcoal rot are patches of stunted or wilted plants. Leaves remain attached after plant death. The fungus produces numerous tiny, black fungal structures called microsclerotia that are scattered throughout the pith and on the surface of taproots and lower stems. These microsclerotia give the lower stem and... Read More

Downy Mildew of Soybean

Downy mildew of soybean is common but seldom causes serious yield loss. Lesions occur on upper leaf surfaces as irregularly shaped, pale green to light yellow spots that enlarge into pale to bright yellow spots. Older lesions turn brown with yellow-green margins. Young leaves are more susceptible, so disease is often found in the up... Read More

Frogeye Leaf Spot of Soybean

Frogeye leaf spot of soybean occurs across the United States and in Ontario, Canada. Frogeye leaf spot can cause significant yield loss when widespread within a field. Leaf lesions are small, irregular to circular in shape, and gray with reddish-brown borders. Most commonly occurring on the upper leaf surface, lesions start a... Read More

Fusarium Root Rot and Wilt of Soybean

Fusarium is a very common soil fungus, and more than 10 different species are known to cause root rot. However, the economic impact on yield is not well documented. Infected seedlings exhibit poor or slow emergence and are often stunted. Root rot appears as reddish-brown to dark brown discolored roots and poor nodulation. Foliar symptoms of Fusarium wilt includ... Read More

Other Nematodes of Soybean (Sting, Lesion, Reniform, and Lance)

Many species of nematodes that feed on soybean roots exist and include the sting nematode, lesion nematode, reniform nematode, and lance nematode in addition to soybean cyst nematode and root-knot nematode. Symptoms of nematodes feeding on roots include poor or uneven growth and stand development, stunted growth, and foliar chlorosis. Often yield loss can occur even when there are no above ground... Read More

Peanut Mottle Virus of Soybean

Peanut mottle virus is mainly found in the southern United States and is transmitted by aphids. Symptoms include yellow spots that form blotches intermixed with green areas of the leaves and patterns of rings or lines may also form. Lab testing is required to confirm if plants have this virus. Read More

Phomopsis Seed Decay of Soybean

Phomopsis seed decay of soybean can greatly affect seed quality. Phomopsis-infected seed are cracked and shriveled and are often covered with chalky, white mold. If infected seeds are planted, emergence may be low due to seed rot or seedling blight. Infected seedlings have reddish-brown, pinpoint lesions on the cotyledons or r... Read More

Phyllosticta Leaf Spot of Soybean

Phyllosticta leaf spot lesions most often occur on leaves and are circular, oval, and irregular or V-shaped. Lesions appear gray or tan and have a narrow, dark margin. In older lesions, numerous small, black specks (i.e., pycnidia) may be visible. The fungus likely survives in infested crop residue and can be seed tra... Read More

Phytophthora Root and Stem Rot of Soybean

Phytophthora root and stem rot of soybean can occur at any growth stage from seed to maturity. Early season symptoms include seed rot and pre- and postemergence damping off. The most characteristic symptom of Phytophthora root rot is a dark brown lesion on the lower stem that extends up from the taproot of the plant. The lesion often reaches as high as several nodes and... Read More

Pod and Stem Blight of Soybean

Pod and stem blight is characterized by black, raised specks that appear in linear rows on mature soybean stems. These specks are fungal reproductive structures known as pycnidia. Pycnidia can also cover pods, but they may not follow the linear pattern seen on stems. These signs are most prevalent from R6... Read More

Powdery Mildew of Soybean

Powdery mildew of soybean is the most common and characteristic sign of powdery mildew is white, powdery fungal growth that can cover all aboveground plant parts, particularly the upper leaf surface. Later symptoms may include plant tissue yellowing and premature defoliation. Powdery mildew usually does not appear until mid- to late reproductiv... Read More

Purple Seed Stain of Soybean

Soybean seeds with purple seed stain can be symptomless or have pink to purple spots extending from the hilum. Discoloration can cover the entire seed or appear as small spots. Crop value may be lowered by dockage or seed certification denial, but yield is not reduced. Purple seed stain incidence can be increa... Read More