Discuss the diseases affecting beans, their symptoms and how they can be controlled

1.Bean Rust (Uromycesphaseoliappandiculatus)
-Important fungal pathogen of beans
-Transmitted from plant to plant by air born pores or rain splash
-It is normally devastating under wet cloudy weather which encourage spore germination and ---growth of lesions
-Has a wide host range
-Have many physiological races thus breeding for resistance is difficult.

Symptoms:
i. Small numerous red pustules on the underside of the leaf
ii. On the top side of the leaf are yellow circles with green spot at the centers called chloric halo
iii. Leaf deformation and premature leaf shade under heavy infestation.

Control:
i. Use of resistant varieties where they exist e.g Mexican 102
ii. Spray with fungicide like Dithio carbonate or copper base fungicides
iii. Destroy crop residues or debris
iv. Crop rotation

2.Bean Anthracnose (Colletotricumlindemothianum)
-This is the most important and prevalent fungal disease of beans
-The disease is worldwide in distribution
-Has a wide host range
-It has a number of distinct modes of transmission such as:
-Through infected seeds
-Infected residue and leguminous seeds found in soil
-Through rain splash
-Occur mechanically during wet weather either by man, animals or machinery

Symptoms:
i. Brown or black sunken lesions on the underside of leaves, stems, petioles and pods
ii. The shape of lesion vary depending on the plant part affected. For stems and petioles the lesions are longitudinal, on pods they are circular with distinctive black margins, on leaves the lesions occurs as black mass on the underside of veins which is associated with leaf distortion.

Control:
i. Use of resistant varieties if available
ii. Cultural practices such as crop rotation, destruction of affected plant residues
iii. Use of clean seeds – certified seeds or treated seeds using systemic fungicide such as Benomyl.
iv. Spray using fungicides

3.Halo Blight (Psedomonasphaseolicolla)
-This a bacteria disease
-Has a wide host range. Greatest damage is however caused in beans
-Mode of transmission is mainly through wind driven rain
-Bacteria enter through stomata and through any injury on the leaf. Thus avoid unnecessary abrasions on the plant.
-The disease is also transmitted through infected seeds. The bacteria is hidden between cotyledons and under the seed coat
-Transmission also occurs through the soil

Symptoms:
i. Small round death areas on leaves or pods surrounded by yellow tissue called “halo”
When the lesions become large, they develop water soaked appearance and the death centers fall off.
ii. On pods, lesions are small, dark green and have the water soaked appearance
iii. Seeds from affected plants are small and shrunken

Control:
i. Mainly through the use of clean seeds
ii. Crop rotation
iii. Destruction of crop residues

iv. Use of copper based sprays

4.Bean Common Mosaic Virus (BCMV)
-Viral disease with wide host range and worldwide distribution
-Transmitted through infected seeds, machinery, by aphids through feeding

Symptoms:
Wide range of symptoms that include:
i. Yellow mottling or chlorosis of leaves
ii. Leaves are brittle and distorted
iii. The plant has stunted growth
iv. Pods are deformed and contain few seeds

Control:
i. Use of resistant cultivars
ii. Use of clean seeds or uninfected seeds or certified seeds
iii. Early planting to escape the attack
iv. Use of insecticides to control aphids
v. Uprooting infected plants in small fields.

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Titany answered the question on August 16, 2021 at 11:30