Despite high yields in many areas, late-season soybean diseases showed up throughout MFA's trade territory this last cropping season. Keep an eye out for these yield robbers and plan your soybean management accordingly.

Reports of late-season diseases on soybeans are still coming in. Sudden death syndrome has been widespread and severe in central and northern Missouri. Septoria brown spot and frogeye leaf spot have been causing yellowing or browning of leaves and premature leaf drop in fields throughout central and northern Missouri. Cercospora kikuchii and Colletotrichum species have been causing leaf spot, yellowing and shoot dieback in fields in northeastern Missouri. Charcoal rot is evident in fields that suffered moisture stress earlier in the season or in areas suffering from drought conditions this fall.

Yield losses from these late-season diseases vary depending on when symptoms occurred, number of plants infected, severity of disease and weather conditions. In some cases, although yellowing of the upper nodes may be quite widespread and spectacular in a field, damage is limited to the uppermost leaves and pods, so yield loss should be minimal. In other cases, especially with sudden death syndrome, the entire plant may have been killed prematurely. If large areas of a field are affected, yield losses are greater.

Management strategies can prevent or minimize these diseases next season.

Sudden death syndrome (SDS)
SDS is caused by a strain of Fusarium solani. It may appear several weeks before flowering but is more pronounced after flowering. Foliage symptoms begin as scattered yellow blotches in the interveinal leaf tissue. These yellow blotches may increase in size and merge to affect larger areas of leaf tissue.

Yellow areas may turn brown, but veins remain green, giving the leaves a striking appearance. Infected plants may wilt and die prematurely. Severely affected leaflets may drop off the plant leaving the petiole attached, or they may curl upward and remain attached to the plant.

Root systems may show deterioration and discoloration of lateral roots and taproot. When split open, internal tissues of the taproot and stem may show a light-gray to light-brown discoloration.

Management strategies:
Management options for SDS are limited but should include planting varieties that have performed well where SDS has been a problem, improving drainage in poorly drained fields, avoiding compaction, staggering planting dates, delaying planting until soils are warm and dry, avoiding continuous crop soybean, maintaining good crop vigor, avoiding crop stress--including stress from soybean cyst nematode--and harvesting fields with SDS in a timely fashion.

Septoria brown spot
Like its name, Septoria brown spot causes small brown spots on the unifoliolate and lower trifoliolate leaves. The individual spots may run together forming irregularly shaped brown blotches on the leaves. Infected leaves may yellow and drop prematurely. Brown spot starts on the lower portion of the plant.

Under favorable weather conditions (warm, wet weather), the disease may move up through the plant. Brown spot was evident in many Missouri soybean fields this season. Hot and drier weather during July slowed disease development, but rains later in August seem to have triggered brown spot development.

Symptoms move up through the canopy of soybean plants. Lower leaves show heavy spotting and yellowing and drop prematurely. Upper leaves show spotting and yellowing. Fields that have a yellow cast from the road may be showing symptoms of Septoria brown spot rather than SDS.

The fungus that causes this disease, Septoria glycines, survives in infested residues left on the soil surface. Fields with continuous soybean production are more likely to show damage.

Management strategies:
Planting disease-free, good-quality seed of resistant

varieties, rotating crops with at least one year between soybean crops and maintaining good plant vigor should reduce losses from Septoria brown spot.

Frogeye leaf spot
Frogeye leaf spot begins as small, reddish-brown circular lesions on soybean leaves. The individual lesions do not increase greatly in size, but as they mature, the center of the lesion turns light tan to gray. The mature lesions have a light center with a dark purple or brown border.

On severely infected leaves, the lesions may merge, killing larger areas of leaf tissue. These areas may drop out, giving the leaves a tattered or lacy appearance. From a distance, fields with high levels of frogeye leaf spot may have a dry, brown cast.

The fungus that causes this disease, Cercospora sojina, can survive in infested residues left on the soil surface. Fields with continuous soybean production are more likely to show damage. The disease is favored by warm, wet weather, high humidity and conditions that increase moisture levels in the canopy.

Shaded fields, fields with heavy tree growth along the edges and river bottom fields are more likely to have frogeye leaf spot.

Management strategies:
Planting disease-free, good-quality seed of resistant

varieties, rotating crops with at least one year between soybean crops and maintaining good plant vigor should reduce losses from frogeye leaf spot.

Cercospora leaf spot and purple seed stain
Cercospora kikuchii can infect soybean seeds, pods, stems and leaves but is commonly found on the seed. Infection primarily occurs on the uppermost leaves and begins as reddish-purple to reddish-brown, angular to somewhat circular lesions on the soybean leaves. These lesions coalesce to kill the leaf tissue. The uppermost trifoliolate leaf and petiole may be blighted and brown.

The most striking symptom is the premature yellowing and blighting of the youngest leaves over large areas of the field.

In most fields, the symptoms do not progress down the plants more than one or two nodes. Pods at the uppermost node may develop round, reddish-purple to reddish-brown lesions.

This pathogen can infect seed, causing purple seed stain. Infected seeds show a discoloration ranging from pink to pale purple to dark purple.

The discoloration may range from small specks to large blotches. Temperatures of 82 to 86 degrees with high humidity favor disease development.

Management strategies:
Because this fungus can infect seed, seed from infected fields should not be used for seed. If infected seed must be planted, seed lots should be cleaned and a seed treatment fungicide used. Rotating soybeans with crops other than legumes will reduce Cercospora leaf spot and blight.

Anthracnose
Anthracnose is caused by Colletotrichum truncatum and several other Colletotrichum species. Typically, anthracnose is a late-season stem and pod disease of soybeans. Symptoms occur on stems, pods and petioles as irregularly shaped, light- to dark-brown spots, streaks or lesions. Eventually black fungal structures may be evident in these lesions.

Anthracnose may also cause a tipblight. The tipblight phase of anthracnose causes a yellowing or browning of the uppermost leaves and pods. The blighted tips may dry up and die prematurely.

Anthracnose is favored by warm, wet weather, and the tipblight phase of anthracnose is most likely to occur after a rainy period.

Management strategies:
This fungus may also infect seed, so seed from heavily infected fields should not be used for planting. If infected seed must be planted, seed lots should be thoroughly cleaned and appropriate seed treatment fungicide used. Rotating crops with at least one year out of soybeans will also help reduce anthracnose.

Charcoal rot
Charcoal rot may cause a seedling infection in soybeans, but it is more common later in the season. Infected plants are less vigorous and may have smaller leaves. Leaves may turn yellow and wilt. The taproot and lower stem may develop a silvery-gray to light-gray discoloration of the epidermis.

Fine black specks or microsclerotia may be evident in tissues below the epidermis and eventually in epidermal tissues. If the lower stem and taproot are split open, a reddish-brown to blackish discoloration may be seen in vascular tissues of the taproot and stem.

The fungus that causes charcoal rot, Macrophomina phaseolina, is a common soil fungus in Missouri. Corn and grain sorghum may also be hosts of the charcoal rot fungus. Charcoal rot is favored by hot, dry weather so symptoms usually appear at temperatures between 82 to 95 degrees.

Management strategies:
Management of charcoal rot of soybeans should include rotating to cereals, cotton or other nonhosts for one or two years. Maintaining good crop vigor through the season will help reduce losses from charcoal rot.