Downy Mildew of Pea
Causal Organism
Name: Peronospora pisi
Classification:
Kingdom: Chromista
Phylum: Oomycota
Class: Oomycetes
Order: Peronosporales
Family: Peronosporaceae
Genus: Peronospora
Species: Peronospora pisi
Symptoms
Foliar Symptoms:
Yellowing:
Initial yellowing of leaf tissue, often in patches.
Downy Growth:
Grayish to purplish downy fungal growth on the underside of leaves, particularly in humid conditions.
Leaf Curling:
Affected leaves may curl and become distorted.
Stem and Pod Symptoms:
Stunting: Infected plants may exhibit stunted growth.
Stem Lesions:
Dark, watersoaked lesions on stems.
Pod Discoloration:
Pods may show discoloration and have fewer, poorly developed seeds.
Systemic Infection:
Severe infections can lead to systemic symptoms, with the entire plant showing signs of wilting, yellowing, and poor development.
Etiology
Downy mildew of pea is caused by Peronospora pisi, an oomycete pathogen. The pathogen thrives in cool, moist conditions and spreads rapidly under favorable environmental conditions. Key factors contributing to the disease include:
Humidity: High humidity or prolonged leaf wetness is essential for spore germination and infection.
Temperature: Optimal temperatures for disease development range from 10°C to 20°C (50°F to 68°F).
Soil Moisture: Excessive soil moisture and poor drainage can create conditions favorable for the pathogen.
Disease Cycle
1. Primary Inoculum:
The pathogen survives in plant debris, soil, or infected seed as oospores or mycelium.
2. Spore Production:
In the presence of moisture, oospores germinate to produce sporangia, which release motile zoospores.
3. Infection:
Zoospores infect host tissues, penetrating through stomata or directly through the epidermis.
4. Symptom Development:
Infected tissues develop symptoms such as yellowing, downy growth, and leaf curling.
5. Secondary Spread:
Sporangia formed on infected tissues are dispersed by wind, rain, or irrigation, leading to secondary infections.
6. Overwintering:
At the end of the growing season, the pathogen overwinters as oospores in plant debris or soil.
Management
Effective management of downy mildew in peas involves an integrated approach combining cultural practices, resistant varieties, and chemical controls:
1. Cultural Practices:
Crop Rotation: Rotate crops with nonhost plants to reduce the buildup of the pathogen in the soil.
Sanitation: Remove and destroy infected plant debris after harvest to reduce overwintering inoculum.
Proper Spacing: Ensure adequate plant spacing to promote air circulation and reduce leaf wetness.
Irrigation Management: Avoid overhead irrigation to reduce leaf wetness duration and opt for drip irrigation if possible.
2. Resistant Varieties:
Plant Resistance: Use pea varieties that are resistant or tolerant to downy mildew. Check with local agricultural extension services for recommendations on resistant cultivars.
3. Chemical Control:
Fungicides: Apply appropriate fungicides as a preventive measure or at the first sign of disease. Common fungicides include those containing active ingredients like metalaxyl, fosetylAl, and copperbased compounds. Follow label instructions and rotate fungicides with different modes of action to prevent resistance development.
4. Environmental Management:
Reduce Humidity: Improve field drainage and avoid planting in lowlying areas where moisture tends to accumulate.
Monitor Weather Conditions: Keep an eye on weather forecasts and apply fungicides before predicted periods of high humidity or rainfall.
By implementing these strategies, the impact of downy mildew on pea crops can be minimized, ensuring healthier plants and better yields.
Powdery Mildew of Pea
Causal Organism
Powdery mildew of pea is primarily caused by the fungus Erysiphe pisi. Another related fungus, Erysiphe polygoni, can also infect peas under certain conditions.
Classification:
Kingdom: Fungi
Phylum: Ascomycota
Class: Leotiomycetes
Order: Erysiphales
Family: Erysiphaceae
Genus: Erysiphe
Species: Erysiphe pisi
Symptoms
White Powdery Growth:
The most characteristic symptom is the white, powdery fungal growth that appears on the surfaces of leaves, stems, and pods. This growth can be easily rubbed off.
Leaf Distortion:
Infected leaves may become curled, distorted, and chlorotic (yellowish).
Reduced Photosynthesis:
As the disease progresses, the dense fungal growth can reduce the photosynthetic ability of the plant.
Premature Leaf Drop:
Severely affected leaves may die and drop prematurely.
Stunted Growth:
Infected plants may exhibit stunted growth and reduced vigor.
Yield Reduction:
Pods may be undersized, deformed, and fewer in number, leading to reduced yield.
Etiology
Powdery mildew of pea is caused by the fungal pathogen Erysiphe pisi. The fungus thrives in environments with high humidity and moderate temperatures, typically between 1525°C (5977°F). Unlike many other fungal pathogens, powdery mildew does not require free water on leaf surfaces to infect the plant, which allows it to spread under relatively dry conditions.
Disease Cycle
1. Overwintering:
The fungus overwinters as mycelium in infected plant debris or as cleistothecia (sexual spores) on plant residues.
2. Spore Dispersal:
In the spring, as conditions become favorable, conidia (asexual spores) are produced and dispersed by wind to new host plants.
3. Germination and Infection:
Upon landing on a susceptible host, the conidia germinate and penetrate the plant tissues, usually through the epidermal cells.
4. Colonization:
The fungus colonizes the plant surface, forming a mycelial network and producing more conidia. This leads to the characteristic white powdery appearance.
5. Reproduction:
The fungus continues to produce conidia throughout the growing season, allowing for multiple infection cycles. Sexual reproduction can also occur, leading to the formation of cleistothecia which can contribute to overwintering.
Management
1. Cultural Practices:
Resistant Varieties: Plant resistant pea varieties when available to reduce the impact of the disease.
Crop Rotation: Practice crop rotation with nonhost crops to reduce the buildup of the pathogen in the soil.
Plant Spacing: Ensure adequate spacing between plants to improve air circulation and reduce humidity around the foliage.
Removal of Infected Debris: Remove and destroy infected plant debris after harvest to reduce overwintering inoculum.
2. Chemical Control:
Fungicides: Apply fungicides as a preventive measure or at the first sign of infection. Commonly used fungicides include sulfur, neem oil, and synthetic fungicides like myclobutanil or trifloxystrobin. Follow label instructions and local regulations regarding fungicide use.
3. Biological Control:
Biocontrol Agents: Utilize biocontrol agents such as Bacillus subtilis or other beneficial microorganisms that can inhibit the growth of powdery mildew fungi.
4. Environmental Management:
Irrigation Practices: Avoid overhead irrigation to reduce leaf wetness, which can contribute to favorable conditions for the pathogen.
Temperature and Humidity Control: In greenhouse settings, control temperature and humidity to create less favorable conditions for the development of powdery mildew.
By combining these management strategies, it is possible to effectively control powdery mildew of pea and minimize its impact on crop yield and quality.
Rust of Pea
Causal Organism
Name: Uromyces pisi
Classification:
Kingdom: Fungi
Phylum: Basidiomycota
Class: Pucciniomycetes
Order: Pucciniales
Family: Pucciniaceae
Genus: Uromyces
Species: U. pisi
Symptoms
Initial Symptoms:
Small, chlorotic spots appear on the upper surface of the leaves.
Pustules:
The most characteristic symptom is the formation of reddish-brown pustules (uredinia) on the undersides of leaves, stems, and pods.
Severe Infection:
In severe cases, leaves may turn yellow and drop prematurely. Stems and pods can also become distorted and exhibit similar pustules.
Telia:
Late in the season, black telia (the overwintering stage) may form, which are visible as black spots.
Etiology
Pathogen Introduction: The rust fungus Uromyces pisi infects peas through airborne uredospores.
Favorable Conditions: Moisture (dew or rain) and mild temperatures (1525°C or 5977°F) favor spore germination and infection. Extended periods of leaf wetness are crucial for the disease to establish.
Lifecycle: The pathogen has a polycyclic lifecycle, producing multiple generations of uredospores throughout the growing season, leading to repeated infections and disease buildup.
Disease Cycle
1. Overwintering:
The fungus overwinters in the telial stage on crop debris or alternative host plants.
2. Sporulation:
In the spring, teliospores germinate to produce basidiospores, which infect the pea plants and initiate the disease cycle.
3. Primary Infection:
Basidiospores infect young leaves, leading to the formation of uredinia (pustules).
4. Secondary Infection:
Uredinia produce uredospores that are winddispersed and cause secondary infections on other parts of the same plant or neighboring plants.
5. Reproduction:
The cycle of spore production, dispersal, and infection can repeat multiple times in one growing season, depending on environmental conditions.
6. Telia Formation:
Late in the season, the fungus forms telia, which produce teliospores that overwinter and start the cycle again the following year.
Management
1. Cultural Practices:
Crop Rotation: Avoid planting peas in the same location for consecutive years to reduce the buildup of inoculum.
Resistant Varieties: Use pea varieties that are resistant or tolerant to rust.
Sanitation: Remove and destroy crop residues and volunteer plants that can harbor the pathogen.
Spacing and Pruning: Ensure proper spacing and pruning to enhance air circulation and reduce leaf wetness duration.
2. Chemical Control:
Fungicides: Apply fungicides prophylactically or at the first sign of disease. Fungicides such as those containing chlorothalonil, mancozeb, or myclobutanil can be effective. Follow label recommendations and use fungicides with different modes of action to prevent resistance development.
3. Biological Control:
Antagonistic Microorganisms: Research and application of biocontrol agents such as Trichoderma spp. and Bacillus subtilis may offer some level of disease suppression.
4. Environmental Management:
Irrigation Practices: Use drip irrigation instead of overhead irrigation to minimize leaf wetness.
Weather Monitoring: Implementing a disease forecasting system based on weather conditions can help in timely fungicide applications.
Effective management of rust of pea involves integrating multiple strategies, including cultural practices, resistant varieties, chemical control, and biological control measures, to reduce the incidence and severity of the disease.