Write short notes on the following plant diseases. (a) blackpod of cocoa; (b) leaf blight of cassava.
Explanation
(a) Blackpod disease of cocoa (i) this is fungal disease of cocoa
(ii) causal organism: phytophthora palmivora
(iii) causes heavy yield loss most especially, in areas of high rainfall which helps in the transmission of spores of the causal fungus from the infected pods or soil to other areas of the farm.
(iv) Symptoms: – appearance of brown spots on the pod which covers the entire pod surface. – later turn black. – the disease penetrates the pod into the beans, leading to rottening, thereby, reducing the economic value.
(v) Prevention: Remove unwanted plant canopies and allow light penetration by regular pruning. Plant resistant variety e.g. hybrid. Spray with fungicides like perenox, Caocobre sandox. Remove and burn infected pods.
(b) Leaf Blight of Cassava: (i) This is a bacterial disease.
(ii) Causal organism: Xanthomonas manihotis
(iii) Transmission: Through cassava cuttings obtained from infected ones and may also be transmitted through contaminated farm tools, e.g. cutlass, hoes used for both cutting and planting of cuttings.
(iv) Symptoms: Occurs on young leaves as small spots leading to larger ones to form light brown dead areas. Later, the upper young leaves die and drop. Canker of stem and back of stem die and there is gum exudation from stem.
(v) Prevention: Plant resistant variety; remove and destroy affected plants; practise crop rotation.