Influence of certain soil factors on chocolate spot of beans

In the summer of 1941 chocolate spot of beans was widespread in the South-Eastern Agricultural Province and caused much damage to the crop. Soil samples were collected from forty-nine affected fields on a variety of soil types, and the relation between the severity of attack by chocolate spot and the texture, pH, available potassium and available phosphorus determined. Severity of attack was classified into three grades: 'slight', in which only spotting of the foliage occurred; 'moderate', in which death of leaves and blossoms on the three or four lowest nodes occurred; and 'severe', in which there was generally a total loss of crop. No significant relation between severity of attack and soil texture, pH or available potassium was found. A highly significant relation was found to exist between the severity of attack and the amount of available phosphorus in the soil as determined by the method of soil analysis used in this Province. Damage by chocolate spot was generally slight on soils containing 'medium to medium high' or higher amounts of available phosphorus, and generally severe on soils containing low amounts of available phosphorus.