Disease Management

$5,663,000,000*

That's the estimated loss of soybean yield to disease in 2010 alone.

And that's why proper seed treatment and other management measures are crucial. The trend for earlier planting can make your crop susceptible to unpredictable early season temperatures and longer seed germination periods. Many seedling diseases favor temperatures less than 55ºF, which can cause problems for emerging soybean plants.* Pathogens can invade plant roots causing tissue decay, pre-emergence damping off and early post-emergence seeding death.

*Based on January 2011 CBOT soybean price of $11.84 per bushel and the University of Missouri Delta Research Center report "Soybean Disease Loss Estimates for the United States, 1996-2010".

Common Soybean Diseases

Learn more about the common diseases that could threaten your crop and your yield potential. Find out how to identify symptoms, factors that increase risk, and the number of bushels each disease claims per year.

Anthracnose 

Anthracnose: 7,849,000 Bu lost

Anthracnose can be hard to detect when scouting. The big problem is that leaves can be infected without showing symptoms, but delayed treatment can result in yield reduction. Pre- and post-emergence damping-off can be caused by infected seed or infection from infested debris in the soil. Infected seeds can develop brown staining, or gray patches with black specks.

Bacterial Blight 

Bacterial Blight: 7,849,000 Bu lost

Bacterial blight is characterized by lesions that initially appear as small, angular, water-soaked, yellow to light brown spots. They are commonly observed in the mid- to upper canopy, and are mostly on leaves but also on stems, petioles, and pods. They typically occur during cool, wet weather. Lesions may grow together to produce large, dead areas.

Brown Spot (Septoria Leaf Spot) 

Brown Spot (Septoria Leaf Spot): 27,454,000 Bu lost

Brown spot disease appears as small, irregular, dark brown spots, primarily on leaves. Spots first appear on lower leaves during warm, wet conditions, and then progress to upper leaves. With brown spot, leaves become rusty brown or yellow, and drop prematurely late in the season.

 

Charcoal Rot: 38,552,000 Bu lost

Charcoal rot can infect soybeans at any growth stage, but the worst infection is typically seen during the reproductive phase under hot and dry conditions. It is more common in light soils and low organic matter soils, and causes rapid plant death. The distinguishing characteristic of charcoal rot is black speckling on the lower stem from fungal tissue. Also, a reddish brown discoloration of hypocotyl and twinstem abnormality may develop along with microsclerotia that can develop in the vascular tissue and may be so numerous that tissues take on a grayish cast.

Little can be done to control charcoal rot but planting non-host crops for three or more years can decrease disease pressure. Reducing stress on soybean plants can help decrease the risk for charcoal rot. This can be done by not planting extremely high populations, properly managing soil fertility and pH and reducing compaction. Infected seed may be symptomless or microsclerotia may be observed embedded in the seed coat. Using soybean products that are more drought tolerant can also decrease the risk of yield loss due to charcoal rot.

 

Frogeye Leaf Spot: 12,125,000 Bu lost

Frogeye leaf spot, also called Cercospora leaf spot, survives on residue and infected seeds. Warm and humid environments are conducive to development and splashing rain and wind can disperse frogeye leaf spot spores to leaf issues where infection begins.

Leaf lesions begin as water-soaked spots and turn into brown spots with dark, reddish brown margins. Older lesions turn light gray with dark brown margins. Tillage, resistant soybeans and crop rotation are all ways to help reduce disease effects. Applying foliar fungicides from the R2 to R5 growth stage can be effective as well.

Fusarium Damping-off and Root Rot 

Fusarium Damping-Off and Root Rot: 10,627,000 Bu lost

Fusarium can be caused by two different fungi. Rot caused by Fusarium oxysporum usually develops on seedlings, during cool weather and may slow emergence and allow the seedlings to be infected when they are stunted and weak. Symptoms of Fusarium are limited to roots and lower stems and the lesions on taproots appear to be light brown to reddish brown to black. Lesions can also girdle the stem and roots.

 

Phytophtora Root Rot: 38,774,000 Bu lost

Phytophthora root rot is typically found in low, poorly drained areas and during conditions of high moisture can also be found in high ground. The fungus survives in the soil or plant debris for extended periods and may be found at any stage of plant development. Infection is favored by soil temperatures of 70º to 80ºF, and moist to saturated conditions.

Early symptoms may include damping-off, but they are very similar to Pythium. To determine which disease has infected your crop, the best indicator is the soil temperature at the time of planting and germination. Warmer temperatures typically indicate Phytophthora root rot. Additionally, Phytophthora root rot has one unique characteristic to help with the diagnosis: An infected seedling has a chocolate brown discoloration of the stem from the soil line up.

Several tools can be used to help protect against Phytophthora root rot in soybeans. Seed treatments help protect the plants up to 30 days after planting. Resistance genes can protect against specific races of Phytophthora root rot and field tolerance can be built to help protect against late season infection.

Pythium Damping-off and Root Rot 

Pythium Damping-Off and Root Rot: 10,627,000 Bu lost

Plants infected with Pythium can be found in wet, low-lying areas. Several Pythium species can rot seeds before germination, causing pre- and post-emergence damping-off. Severe infections may destroy root tips, producing lesions on taproots which can lead to chlorosis, stunting and wilting of infected plants.

Rhizoctonia Damping-off and Root Rot 

Rhizoctonia Damping-Off and Root Rot: 3,310,000 Bu lost

Rhizoctonia can cause seed rot, damping-off, root rot, and stem rot. Post-emergence damping-off occurs before first trifoliate leaf develops. Infected plants have reddish brown, sunken lesions on the hypocotyls at the soil line, which can cause girdling of the hypocotyls and result in collapsed plants.

Soybean Mosaic Virus (SMV) 

Soybean Mosaic Virus (SMV): 7,849,000 Bu lost

Symptoms depend on the soybean product, virus strain, plant age at infection, and environment. Seeds of infected plants can be mottled, and once infected, plants have fewer pods and are stunted. Leaves have a mosaic of light and dark green areas and the leaf margins can be wavy or curled. Leaf veins do not grow together, which can also occur with herbicide injury.

Stem Canker 

Stem Canker: 6,097,000 Bu lost

Northern and southern stem canker are similar but different fungal spots. Lesions caused by northern stem canker become dark brown and girdle the stem, while lesions caused by southern stem canker rarely girdle the stem. Stem canker is most common in cool and moist conditions during early stages of soybean growth.

 

Sudden Death Syndrome: 3,547,000 Bu lost

Sudden death syndrome is often associated with soybean cyst nematode, highly productive soils, cool temperatures during flowering and significant rainfall before and during flowering. Infection normally occurs in the root system in the late vegetative growth stages, V5 to V8.

Sudden death syndrome leaf symptoms initially include yellow blotches that form between the veins on the uppermost leaves. The blotches then coalesce and eventually turn dark brown. Leaves may roll inward due to lack of water and eventually drop off. Managing soybean cyst nematodes can also help reduce potential infection sites. Additionally, later planting can also help reduce the opportunity for other diseases and insects to invade the roots.

 

White Mold

White mold, or Sclerotinia stem rot, can cause yield reductions and poor seed quality. Overwintering Sclerotia located up to 2" below the soil surface start germinating when soil temperatures are less than 65ºF and moisture levels are high. Infection occurs when plant wounds contact neighboring infected plants.

Water-soaked lesions at stem nodes are the first sign of infection. Lesions girdle the stem, cutting off moisture and nutrients to upper plant parts. To reduce the risk of white mold, plant shorter, tolerant products in wide rows. Crop rotations with corn and early control of weeds can also reduce the number of hosts.

Compendium of Soybean Diseases 4th Edition APS Press.​

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