|Root rot||Macrophomina phaseolina|
|Powdery mildew||Oidium sp.|
|Leaf spots||Alternaria sp.|
|Cassava Mosaic Disease (CMD)||Cassava mosaic gemini virus (CMG)|
1. Root rot – Macrophomina phaseolina
Symptoms include yellowing of foliage, reduced leaf size, and eventual death of the plant due to root rot. The affected tissues show shredding of the bark tissues.
Mode of spread
The pathogen spreads through transfer of infested soil by agricultural implements and irrigation water.
The pathogen survives as sclerotia in soil and plant debris.
Drought stress makes the plant weak and susceptible. High soil temperature with rain or irrigation during grain filling stage encourages infection.
- Collection and destruction of infected plant debris.
- Use of antagonistic organisms like T. viride, P. fluorescens as soil application helps to reduce the inoculum.
2. Powdery mildew- Oidium sp.
Leaves, shoots and fruits acquire a dusty white to gray coating which turns into black patches with severe infection. Powdery mildew will begin as discrete, usually circular, powdery white spots. As these spots expand they will coalesce, producing a continuous matt of mildew (similar to dirt or dust).
Mode of spread and Survival
The pathogen spreads through air borne conidia and survives in the infected plant debris.
Temperature of 20 – 210 C is ideal for the disease development
- Dusting sulphur at 40 kg/ha.
3. Leaf spots – Alternaria sp.
The disease creates spots on foliage. Spots are most often brownish, but may be tan or black. Concentric rings or a dark margin around the spot may be present. Over time the spots may combine to enlarge and form larger blotches. Leaves may turn yellow and drop prematurely.
Mode of spread and survival
Wind borne conidia spread the disease and the pathogen survives in the infected seeds.
Low temperature (20 to 250 C), high relative humidity and cloudy weather favour the disease development.
- Seed treatment with thiram or carbendazim at 2 g/kg of seed.
- Spray mancozeb @ 1 kg/ha.
4. Cassava Mosaic Disease (CMD) – Cassava mosaic geminivirus (CMG)
Plants infected with the disease show mosaic with yellow chlorotic spots, distortion and reduction in leaf size.
Transmitted by the whitefly
Summer temperature (30-350 C) favours multiplication of vectors and the disease spread.
- Infected plant should be removed.
- Spray with Monocrotophos @ 500 ml/ha to control vectors