Last week we wrote an article about the high levels of soybean root rots showing up in the region. Although multiple pathogens can cause root rots on soybeans, Rhizoctonia has been consistently showing up this year. Of 8 soybean root samples received in the diagnostic lab in the last two weeks, Rhizoctonia has been isolated from four of them. Similarly, many descriptions and close-up photos sent to us have been consistent with Rhizcotonia root rot: reddish lesions/cankers with distinct margins. We are not saying all the soybean root rots are caused by Rhizoctonia, but the pathogen is definitely a player this year. Plants were stressed this early summer by wet soils which favors fungal pathogens attacking the roots. Other pathogens such as Fusarium are likely also involved in the disease showing up in growers fields this year.
Rhizoctonia root rot is caused by the fungal pathogen Rhizoctonia solani. The pathogen has different ‘Anastomosis groups’ or ‘AG’, which are similar to a ‘race’ or ‘strain’. Common AG groups found on soybean in our area are AG4, AG5 and AG2-2 Depending on the AG, Rhizoctonia solani may also infect other crops, including; dry edible beans, corn and sugarbeets.
Rhizoctonia can infect, stunt and or kill seedlings, and can also damage older plants. Significant yield losses are possible when a high level of infection occurs early. Typical symptoms of Rhizoctonia root rot include sunken lesions near the soil line that are often rusty red/brown in color.
As is the case with all root rots, there are no management strategies available once the plants are up. However, if you have significant root rot damage, a fungicide seed treatment and lengthening your crop rotation may reduce the impact of Rhizoctonia root rot in the future.
Source : ndsu.edu