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Disease Control

Rust

a. Causes
The disease is caused by the fungus Uromyces appendiculatus. This is a very serious disease to French Beans and other food beans.  The Development of the disease is favoured by high humidity conditions.

b. Symptom
The disease is recognized by the presence of slightly raised, small white spots, on the surface of the lower leaf. The spots turn red to dark brown after a few days.

c. Control

  • Crop rotation
  • Use of tolerant varieties.
  • Chemical sprays such as: Baycor 30% EC , Bitertanol, Anvil, Alto 100  SL,  or Dithane M45 should be applied after every two weeks.

Angular Leaf Spot

a. Causes
This is a fungal disease caused by Phaeoisariopsis griseola.

b. Symptoms
Leaves, stalks, and pods have angular brown or red coloured spots with purple edges and grey to brown centres. The leaves may then fall prematurely.

c. Control

  • By use of healthy, certified seeds.
  • Treat Seeds using chemicals such as  fernasan-D, at 3gm per kg of seed.
  • Spray with chemicals such as benomyl (or benlate)

Root Rots

(Quintozene)

a. Causes
These are fungal diseases caused by the fungus Rhizoctonia spp, Pythium spp Sclerotium spp etc.

b. Symptoms
Affected plants show yellowing and drying of stem at soil level. Stunting may also occur.  The crop may also show poor seedling establishment, uneven growth, chlorosis and premature defoliation of severely infected plants.

c. Control

  • Seed dressing with a chemical such as: Fernasan-D , at 3gm per kg of seed, or Quitozene.
  • Drenching with chemicals such as: Brassicol (or Quitozene), Benomyl (or Benlate), or Bavistin, during the vegetative stage.

Bacterial Blights

a. Causes
The condition is caused by Pseudomonas Phaseolicola and Xanthomona phaseoli . It is a serious disease for beans in Kenya, especially in cool and wet areas. The disease is spread through splashing from exuding lesions and plant debris.

b. Symptoms
Plants show ring-like spots on the leaves, drying of leaf margins, yellowing and water soaked pods.

c. Control

  • Use of certified seeds.
  • Roguing and destruction of affected plants.
  • Crop rotation.
  • Chemical sprays using copper based fungicide such as: kocide 101.

Anthracnose

a. Causes
The disease is caused by a fungus known as Colletotrichum lindemuthiamum. The fungus is seed-borne and affects all
aerial plant parts.  It is spread by rain splash, wind or mechanical contact. The disease usually occurs in cool, damp weather.

b. Symptoms
The disease is characterised by appearance of sunken, brown spots with black edges on pods; angular brown sports on leaves; and oblong stripes on stems.

c. Control

  • Use of certified seeds.
  • Field sanitation.
  • Crop rotation.
  • Use of resistant varieties.
  • Foliar sprays using chemicals such as: Benomyl, Mancozeb, propineb.

Bean common Mosaic Virus (BCMV)

a. Causes
The disease is seed-borne and it is transmitted by aphids.

b. Symptoms
The symptoms of this disease vary with variety, stage of growth, and environmental factors.
They includes a mosaic (i.e. mottling, Curling and stunting of leaves,) systemic Necrosis and local malformations.  The leaves may roll, malform and general stunting of the pant.  The plant produces excessive number of Lateral shoots.

c. Control

  • Use of certified seeds.
  • Plant resistant varieties
  • Rouging of infected plants.
  • Control of aphid vectors using insecticides.

Powderly mildew

a. Causes
It is caused by a fungus known as Erysiphe spp.

b. Symptoms
Attacks stems,leaves,flowers, and pods which appear covered with white powdrerly growth which turn black latter. In severe cases the leaves turn yellow and drop off.

c. Control

  • Field hygiene
  • Crop rotation
  • Chemical fungicides eg. Dithane M45, Antracol, Bayleton

Downy mildew

a. causes
Caused by afungus known as perenospora spp.

b. Symptoms
The underside of leaves exhibit white to greyish growth which later cover whole leaf surface.

c. Control

  • Field hygiene
  • Crop rotation
  • Chemical fungicides eg. Dithane M45, Antracol, Bayleton
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