Root rot is primarily a soil-borne disease caused by the fungus Macrophomina phaseolina, which can survive in the soil as sclerotia for several years.
Dry weather conditions following heavy rains, combined with high soil temperatures (35-39°C) and low soil moisture (15-20%), create favourable conditions for the occurrence of this disease.
Damage Symptoms
The fungus causes three types of symptoms: seedling disease, sore-shin, and root rot.
Seedlings (1-2 weeks old) infected by the fungus develop black lesions and girdling of the stem, ultimately causing the death of the seedlings and leaving large gaps in the field.
In the sore-shin stage (4 to 6 weeks old plants), dark reddish-brown cankers form on the stems near the soil surface. These cankers eventually turn dark brown or black, causing the plant to break at the collar region. This leads to the drying of the leaves and the eventual death of the entire plant.
Root rot symptoms typically appear when the plants are near maturity. Sudden and complete wilting, often in patches that form concentric circles can be observed.
When affected plants are pulled up, the root system shows extensive rotting.
The bark of the infected plant may begin to shred, sometimes extending above ground level.
In severe cases, the woody portions of the plant may turn black and become brittle.
Preventive Measures:
Apply neem cake at a rate of 2.5 tons per hectare.
Treat the seeds with Trichoderma viride at 4g/kg or Pseudomonas fluorescens at 10g/kg.
Control Measures:
Spot drench with 0.1% Carbendazim or 0.05% Benomyl.
