As Missouri soybean growers scout fields each summer, symptoms of sudden death syndrome (SDS) become a common concern. However, a new player has entered the game. Red crown rot (RCR) is complicating SDS diagnosis because it produces nearly identical leaf symptoms and develops under many of the same field conditions. 
While both diseases cause the characteristic yellowing (chlorosis) and browning (necrosis) between leaf veins and significantly reduce yields, RCR is an emerging threat in Missouri that requires closer inspection of the stem base and roots for accurate identification. As the disease continues to spread across the state, understanding the critical differences between SDS and RDR has become essential for protecting soybean profitability and making informed management decisions. RCR is caused by the soilborne fungus Calonectria ilicicola. The pathogen survives in soil for many years and infects soybean roots early in the growing season. Once established, it can damage the root system, reducing the plant’s ability to take up water and nutrients. Aboveground symptoms often resemble other soybean diseases, making diagnosis difficult. Infected plants may show: • Yellowing between leaf veins • Premature leaf drop • Stunted growth • Wilting during hot, dry weather • Reduced pod set and smaller seed size The most distinctive symptom appears at the base of the stem. When soil is removed from the crown, growers may notice bright reddish-orange fungal structures attached to the stem near the soil line. These “red crowns” give the disease its common name and are an important diagnostic feature. Below ground, roots are often darkened, decayed and reduced in size.
RCR thrives in moist soils fields with poor drainage, compacted soils, and continuous soybean rotation. The fungus can also survive in infected crop residue and soil, making it difficult to eliminate once established. Extended periods of saturated soil followed by heat stress can increase symptom severity later in the season. In a year of strong rainfall and high moisture, it is imperative farmers scout their beans to look for these concerns early. If soybean plants show SDS-like leaf symptoms, don’t stop at the leaves. Dig plants and examine the crown and roots. The presence of bright red fungal structures at the soil line is an indicator of red crown rot. The absence of bright red fungal structures combined with classic SDS foliar symptoms makes sudden death syndrome the more likely diagnosis.
Since the disease can be mistaken for sudden death syndrome, brown stem rot or other root diseases, proper diagnosis is essential. Laboratory testing may be necessary to confirm its presence. The University of Missouri offers the ability to test RCR for farmers across the state. If you’re in Missouri and need a soybean disease diagnosis, whether you suspect sudden death syndrome, red crown rot or another disease, the best place to send samples is the University of Missouri Plant Diagnostic Clinic, 28 Mumford Hall, 1100 University Ave., Columbia, MO 65211. Red crown rot testing is available at no cost to Missouri farmers through support from the Missouri Soybean Merchandising Council and United Soybean Board.
