Sudden Death Syndrome Look Alike Part I: Red Crown Rot

Characteristic appearance of red crown rot of soybean with the red perithecia at the soil line.

Red crown rot is a disease of extremely limited distribution in Mississippi.  A limited number of counties, all in east Mississippi, have been observed to contain soybean plants infected with red crown rot.  Prior to 2013, red crown rot had been observed in three counties in Mississippi, Chickasaw, Lowndes, and Noxubee.  As of today (9/5/2013), three additional counties have been added with confirmed red crown rot.  During the 2013 season, Clay, Newton and Union counties were confirmed to have red crown rot infected soybean plants.  One important thing to note regarding red crown rot, the foliar symptoms can appear quite similar to SDS.  Since the disease is not widespread in MS only a limited number of fields have been observed to contain the disease.  But, this year in particular, intense red crown rot has been observed in some parts of Noxubee County, in fields that have previously had limited red crown rot infected plants.

Initial symptoms of red crown rot begin as mild chlorosis.

Symptoms

Symptoms of the disease most commonly appear during pod initiation (R3), typically on scattered plants or small groups of plants in fields.  However, rarely have I observed symptoms of the disease at this particular growth stage.  Generally speaking, and from what I have observed in the past, symptoms become more evident as soybean plants enter the mid-R4 to R5 growth stages.  The initial symptoms of the disease will appear as small, interveinal chlorosis (yellowing) in the upper canopy.  As the disease progresses and especially in more advanced stages the leaves can develop an interveinal necrosis similar to SDS.  In addition, split stems reveal an inner vascular staining similar to SDS and some other root diseases observed in the MS soybean production system.  But, with this in mind, some differences exist between red crown rot and SDS.  First and foremost, the main difference between plants affected with SDS and red crown rot has to do with the red discoloration at the base of the soil line.  In the most mature cases of the disease the base of the stem at the soil line can develop a bright red fungal growth of the fungal reproductive fungal structures.  However, in the absence of the perithecia, the steam can be slightly sunken and red in color (but, keep in mind that

Advanced stages of red crown rot include interveinal necrosis similar to SDS.

other diseases, such as stem canker, can produce a similar symptom).  If the fungal structures aren’t observed during the initial scouting, spend some time looking around the area for other affected plants to distinguish the diseases from one another.  One other main difference between red crown rot and SDS has to do with the particular soil class where the disease will be observed.  SDS will not occur on heavy soils so if the field in question contains heavy soil then it is more likely that red crown rot is the disease in question.  One other key difference between SDS and red crown rot has to do with leaf drop.  Generally speaking, plants exhibiting symptoms of SDS will likely hold their leaves.  However, plants exhibiting symptoms of red crown rot will normally shed their leaves prematurely.

Management options

All soybean varieties are considered to be susceptible to red crown rot.

Once the disease has been identified in a particular field, management options for that season are non-existent.  In successive seasons, rotating to a non-host such as corn, cotton or grain sorghum can be beneficial.  However, more than two years may be necessary to reduce the soilborne inoculum and prevent the disease from occurring when soybean is planted back into the field.

Red crown rot symptoms without the red perithecia. Note red area on stem.

Prevention is the best management practice for red crown rot.  Limiting the spread of the pathogen is the most important method for reducing the disease.

Moving equipment and/or soil between fields that have the disease is one way the fungus can be spread to new fields.  In fact, the initial identification of red crown rot in MS can be traced back to the purchase of farm equipment from Louisiana where the disease is much more widespread.

Fungicides are not effective management tools against diseases that affect soybean roots.

Internal stem discoloration indicative of red crown rot.

Red crown rot symptoms in a field of soybean.