Crop diseases continue to be a major challenge for farmers, causing significant yield losses and reducing produce quality. Effective crop production begins with proper disease identification, regular field scouting, and timely intervention before outbreaks become severe.

Farmers can significantly reduce disease pressure by using certified seeds and seedlings, practicing crop rotation, maintaining field sanitation, and ensuring proper spacing for improved air circulation. These practices help prevent the spread of fungal, bacterial, and soil-borne diseases that commonly affect vegetables and other crops.

Early detection remains one of the most powerful tools in crop management. By monitoring crops regularly and responding quickly to disease symptoms, farmers can protect yields, improve produce quality, and increase profitability. Healthy seedlings, preventive management, and continuous learning are the foundation of successful and sustainable farming.

Premagrow

1. Virtual Training: Chillie Export Farmers Date: June 25th m

Location: Google Meet

 

2. Crop Management Skills (CMS) Physical Trainings Date: June 27th – July 25th, 2026

Location: PremaGrow Katani – 0796140566

 

Date: August 08th – September 05th, 2026

Location: PremaGrow Meru – 0769600244

 

3. Farmers Field Day Date: October 2nd, 2026 Location: Kenanie

In collaboration with: Amiran Kenya Ltd

 

Date: February 19th – 20th,2027

Location: PremaGrow Mikumbuni Meru

 

IDENTIFICATION & MANAGEMENT OF CROP DISEASES

 

Facilitator: SINDI MORRIS Date: 21st May 2026

 

Objectives: To Identify…

• Major crop families
• Common diseases, symptoms, & Causes
• Proper disease scouting & diagnosis
• Preventive measures & Management
• Reduce crop losses & improve farm

Introduction: Impact of Crop Diseases

• Reduces crop yield by 20–40% globally

 

• Severe outbreaks can cause up to 60% losses or total crop loss

 

• Lower produce quality and market value

 

• Increase production costs through chemical spraying and labors

 

• Cause post-harvest losses of 20–25% .

 

• Reduce farmer profits and food

Brassica Family

• Cabbage
• Kale
• Broccoli
• Cauliflower

Common Characteristics

• Leafy vegetables
• Sensitive to fungal and bacterial diseases
• Thrive in cool conditions

 

 

Amaranthaceae Family

• Spinach
• Amaranthus (Terere)
• Beetroot

Common Characteristics

• Leafy vegetables
• Fast growing crops
• Sensitive to leaf spots, damping off & nutrient disorders

Importance of Understanding Crop Families

 

 

1. Black Rot

Major Symptoms:

• Yellow V-shaped lesions from leaf edges
• Blackening of leaf veins
• Wilting and leaf drying
• Stunted growth

 

Spreads through:

• Infected seeds and seedlings
• Rain splash and irrigation water
• Farm tools and workers
• Infected crop residues

 

 

 

 

 

 

 

Caused by the bacterium:Xanthomonas campestris pv. campestris

 

2. Downy Mildew

Major Symptoms

• Yellow patches on upper leaf surface
• Grey-purple mold on underside of leaves
• Leaf curling and drying
• Poor head formation in cabbages
• Stunted crop growth

Disease develops rapidly under

• Cool temperatures
• High humidity
• Frequent rains or dew
• Poor air circulation
• Overcrowded crops

 

Caused by a fungus-like pathogen called Hyaloperonospora parasitica

 

Management Practices

1. Management Practice
   1. Use Clean Planting Materials : Use certified disease-free seeds and seedlings
   2. Crop Rotation: Avoid planting brassicas in the same field for seasons
   3. Field Sanitation: Remove and destroy infected plants and crop debris, and weeds
   4. Avoid Excessive Moisture: Avoid Overhead irrigation to Reduce spread through water splash, irrigate early in the day
   5. Proper Spacing: Improves air circulation and reduces humidity
   6. Prevent Field Injuries: Minimize damage during weeding and handling
2. Chemical Management: Use Hy-coxide to prevent. Spray two weeks after transplanting,

 

 

0796 140566 – KATANI 0769600244 – MERU

3.           Club Root Disease

Major Symptoms

Above Ground Symptoms Wilting during hot periods Stunted growth

Yellowing of leaves Poor head formation

Below Ground Symptoms

Swollen & deformed roots (“clubs”) Rotten root system in severe cases

Conditions Favoring the Disease

• Acidic soils (low pH)
• Poor drainage
• Waterlogged fields
• Continuous planting of brassicas
• Contaminated tools and soil movement

 

 

 

 

soil-borne pathogen called: Plasmodiophora brassicae

 

 

 

 

Management and Control

Cultural Practices

• Practice crop rotation for 3–4 years
• Improve field drainage
• Avoid movement of contaminated soil
• Remove infected plants

Soil Management

• Apply agricultural lime to raise soil pH
• Maintain soil pH above 6 where possible.

• Use of commercial organic fertilizers and soil buffers eg solum H20

Chemical Management

• Soil fumigation may help in high-value production systems

• “Once club root is established in the soil, it becomes difficult to eliminate — prevention is very important.”

Fusarium Wilt & Verticillium Wilt

External Symptoms fusarium wilt

 

Both FW& VW are vascular wilt diseases. They attack the plant’s water transport system (xylem), causing wilting, yellowing, & eventually plant death. They affect crops such as tomatoes, peppers, cucumbers, potatoes, eggplants, flowers, & trees

• Yellowing begins on lower leaves
• One-sided wilting is common
• Plants wilt during hot daytime
• Stunting
• Permanent wilting later

Internal Symptoms

• Brown vascular discoloration inside stem

Management and Control

 

Examples Soil Borne Diseases

• Damping off
• Fusarium
• Rhizoctonia
• Pythium
• Phytophthora
• Verticillium
• Nematodes
• Some crucifer diseases g. club root suppression

Example of Control Products

• Metam Sodium
• Forsetyl aluminium (preventive)
• Dazomet (basamid)
• Biofungicides (trychoderma)
• Chloropicrin (restricted in many countries)
• 1,3-Dichloropropene mixtures (restricted use)

Verticilium wilt

External Symptoms

• Yellowing between veins
• V-shaped leaf yellowing
• Gradual wilting
• Usually starts from older leaves
• Stunting

Internal Symptoms

• Light brown vascular discoloration

 

Solanaceous Family

• Tomato
• Pepper
• Black night shade {managu}
• Eggplant

Common Characteristics

• Fruit-bearing
• Perform well under warm conditions
• Highly susceptible to fungal, bacterial, and viral diseases

 

 

0796 140566 – Katani 0769600244 – Meru

 

 

Major Diseases Affecting Solanaceous Crops

 

Fungal Diseases

• Early blight
• Late blight
• Powdery mildew
• Damping off

 

Bacterial Diseases

• Bacterial wilt
• Bacterial spot
• Bacterial canker

Viral Diseases

• Tomato Yellow Leaf Curl Virus (TYLCV)
• Mosaic viruses

 

Management disease

• Blossom end rot
• Commonly Affected Crops
• Tomato
• Pepper

 

 

 

 

 

 

1.   Early Blight

Conditions Favoring Early

 

 

Management and Control Cultural Practices:

 

Blight

• Warm temperatures
• High humidity
• Frequent leaf wetness
• Poor field sanitation

Symptoms

• Brown spots with concentric rings (“target spots”)
• Yellowing around lesions
• Lower leaves affected first
• Premature leaf drop
• Stem and fruit lesions

• Remove infected leaves
• Practice crop rotation
• Improve spacing and airflow
• Avoid overhead irrigation

Chemical Control

Recommended fungicides:

• Mancozeb
• Chlorothalonil
• Azoxystrobin – distrobin/
• Beyond
• Difenoconazole mixtures

Caused by the fungus Alternaria solani.

 

 

2.  Late Blight

 

Conditions Favouring Late Blight

• Cool and wet conditions
• High humidity
• Continuous rainfall

Symptoms

• Water-soaked dark lesions on leaves
• Rapid blighting of foliage
• White mold growth under leaves
• Fruit rot
• Rapid crop collapse

Management and Control

Cultural Practices

• Use healthy seedlings
• Remove infected plants
• Improve drainage and airflow
• Avoid excessive moisture Chemical Control Recommended fungicides:
• Metalaxyl + Mancozeb
• Cymoxanil mixtures
• Propamocarb hydrochloride
• Fluopicolide mixtures
• Copper-based fungicides

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Caused by     Phytophthora infestans.

 

Comparison between Early and late blights.

Early Blight (Deuteromycetes)

• Brown spots with concentric rings
• “Target spots” with yellow halo
• Gradual spread
• Defoliation and reduced yield
• Dark sunken lesions near stalk

Fungicides effectiveness

• Mancozeb, Azoxystrobin, Difenoconazole,

Best Management

• Sanitation and preventive sprays

Late Blight (Oomycetes)

• Water-soaked dark lesions
• Large dark greasy
• Very rapid spread
• Sudden crop collapse
• Brown firm fruit rot

Fungicides effectiveness

• Metalaxyl + Mancozeb, Cymoxanil,

Best Management

• Early preventive spraying and moisture control

Common symptoms to check when scouting

 

Common symptoms to check when scouting:

• Leaf spots
• Wilting
• Yellowing
• Stem lesions
• Fruit rots
• Curling of leaves
• Stunted growth

Conditions Favoring Diseases:

• High humidity
• Excess rainfall
• Poor field sanitation
• Infected seedlings
• Continuous cropping
• Poor spray programs

 

Bacterial Diseases in Solanaceous Crops:

1. Bacterial Wilt

Conditions Favoring Disease

• Warm temperatures
• Waterlogged soils
• Continuous tomato production
• Poor drainage

Symptoms

• Sudden wilting without yellowing
• Plants wilt during the day
• Brown discoloration inside stems
• Plant eventually

Management and Control Cultural Practices

• Practice crop rotation
• Improve drainage
• Remove infected plants
• Avoid movement of contaminated

Chemical/Biological Support

• Copper-hydroxide and oxide reduces spread
• Biological products may help suppress bacteria

 

 

 

 

 

 

Caused by: Ralstonia solanacearum

 

0796 40566 – KATANI 0769600244 – MERU

 

 

• Rain splash
• Overhead irrigation

Symptoms

• Small dark leaf spots
• Yellow halos around lesions
• Leaf drop
• Raised spots on fruits

• Avoid overhead irrigation
• Remove infected plant debris
• Practice crop rotation
• Improve spacing

Chemical Control

• Copper-based bactericides
• Copper + Mancozeb mixtures

 

 

 

 

 

 

 

 

 

 

Caused by Xanthomonas species.

 

 

3.  Bacterial Canker

 

Conditions Favoring Disease

• Infected seeds and seedlings
• High humidity
• Plant injuries

 

 

Symptoms

• Wilting on one side of the plant
• Brown stem streaks
• “Bird’s eye” spots on fruits
• Leaf edge

Management and Control Preventive Practices

• Use certified seeds
• Avoid plant injuries

Cultural Practices

• Remove infected plants
• Practice crop rotation
• Maintain field hygiene

Chemical Management

• Hy-coxide help reduce spread

.

• Preventive management is most effective

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Caused by Xanthomonas species.

 

4.

Blossom End Rot

Blossom end rot is a physiological disorder mainly caused by: Calcium deficiency in developing fruits

The problem is worsened by:

• Irregular watering/ Moisture stress
• Excess nitrogen
• Poor root development
• High salinity
• Root

5.  Anthracnose Disease

It causes dark sunken lesions on fruits, stems, and leaves, especially during warm humid conditions.

 

Controled by

Strobilurins (Azoxystrobin)

Triazoles (Difenoconazole, Tebuconazole)

Protectants (Mancozeb, Copper)                                                            It is mainly caused by fungi in the genus

Colletotrichum.

 

6.

Powdery Mildew

Powdery mildew appears as white powder-like growth on leaves and stems. It reduces photosynthesis and weakens plants.

Symptoms

• White powdery coating on leaves
• Yellowing and curling of leaves
• Premature leaf drying
• Reduced plant vigor and yield

Management

• Improve spacing and airflow
• Avoid excessive nitrogen
• Remove infected leaves

7.   Purple Blotch

Symptoms

• Small whitish sunken spots turning purple-brown
• Yellow margins around lesions
• Leaf tip drying and collapse
• Reduced bulb size in onions

 

 

General Management for These Diseases

• Use certified clean seed/seedlings
• Practice crop rotation
• Avoid overhead irrigation late in the day
• Improve spacing and airflow
• Remove infected plant debris
• Apply preventive fungicides early before severe infection develops

General Disease Management

• Use certified seedlings
• Practice crop rotation
• Scout fields regularly
• Remove infected plants
• Use preventive spray programs
• Control insect vectors
• Maintain proper spacing and drainage

 

 

• Disclaimer: “Healthy seedlings and early disease detection are the foundation of successful crop production.”

 

 

 

 

 

 

 

0796140566 /

0780573464 –                    Katani

0769600244 /

0733318029- Meru

 

+254 796 140 566 – Katani

+254 769 600 244 – Meru

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premagrow@gmail.com / info@Premagrow.com