Soybeans Dropping Leaves Too Early In Patches? Could Be Charcoal Rot

 

A few fields scouted last week had soybean plants dropping leaves prematurely. Upon checking these plants, they were found to be infected with charcoal rot (Figure 1). Areas in a field with plants droppings leaves earlier than normal should be scouted to rule out diseases such as charcoal rot, brown stem rot, or sudden death syndrome.

 

 

Charcoal rot is caused by a fungal pathogen Macrophomina phaseolina. This pathogen survives both in the soil and in plant residues and also infects the plant through the roots. The pathogen clogs the roots which leads to a blockage of water and mineral salts being transported.  Infection takes place early in the growing season but symptoms develop later in the season when plants are under stress. The presence of soybean cyst nematode in a field exacerbates charcoal rot symptoms.

 

 

 

To differentiate charcoal rot from other diseases which may cause early leaf drop such as sudden death syndrome, uproot a symptomatic plant in the middle of the patch and peel off the tap root epidermis. If small black speckles are observed the plant is infected with charcoal rot (Figure 2). Also splitting the stem will show the black speckles resembling charcoal powder, hence the name charcoal rot .