Diseases of Field & Horticultural Crops & Their Management-II
Unit-V
Spices and Ornamental Crops
Chillies
Chillies, also known as hot peppers or chilli peppers, are a popular spice crop that is widely grown throughout the world for their pungent flavour and medicinal properties. However, like all crops, chillies are susceptible to a range of diseases that can impact their growth and yield.
Two common diseases that affect chillies are fruit rot and leaf curl. Here's what you need to know about each of these diseases:
Fruit Rot
Symptoms:
- Symptoms of fruit rot in chillies include the appearance of water-soaked lesions on the fruits.
- These lesions may enlarge and become sunken, often turning dark in color.
- Infected fruits can develop soft spots and may show signs of mold growth.
- In advanced stages, the entire fruit may become decayed and shriveled.
Etiology:
- Fruit rot in chillies can be caused by various fungal pathogens, including Colletotrichum spp. and Phytophthora spp..
Disease Cycle:
- Infection: Fungal spores land on chilli fruits and gain entry through wounds, cracks, or natural openings.
- Lesion Development: Once inside the fruit, the fungi grow and cause water-soaked lesions.
- Spore Production: As the lesions expand, fungal structures develop and produce spores.
- Secondary Infections: Spores are released and can infect neighboring fruits or other plants.
- Disease Spread: The disease can spread rapidly under favorable conditions, leading to fruit decay.
Management:
- Sanitation: Remove and destroy infected fruits and plant debris.
- Mulching: Use mulch to prevent soil-borne pathogens from splashing onto fruits.
- Avoid Overhead Irrigation: Watering at the base of plants can help prevent moisture on fruits.
- Proper Spacing: Adequate spacing between plants for air circulation and light penetration.
- Fungicides: Apply fungicides as per recommendations during fruit development.
- Resistant Varieties: Consider planting chilli varieties with resistance to specific fruit rot pathogens.
- Crop Rotation: Avoid planting chillies in the same location year after year.
- Weed Control: Remove weeds that may harbor disease-causing pathogens.
- Nutrient Management: Maintain proper fertilization to promote plant health.
- Timely Harvest: Harvest fruits at the proper stage of maturity to reduce susceptibility to infection.
Effective management of chilli fruit rot involves a combination of cultural practices, proper sanitation, and timely fungicide applications. Preventing the spread of spores, reducing conditions conducive to disease development, and using resistant varieties are key strategies to protect chilli crops from fruit rot and minimize yield losses.
Leaf Curl
- Leaf curl in chillies is characterized by curling and upward rolling of the leaves.
- The leaves may become thickened and brittle.
- The affected leaves often show a pronounced yellowing or bronzing of the upper surface.
- Stunted growth and reduced fruit production may also be observed.
Etiology:
- Leaf curl in chillies is typically caused by a group of viruses known as Begomoviruses.
- These viruses are transmitted by whiteflies (Bemisia tabaci).
Disease Cycle:
- Transmission: Whiteflies feed on infected plants, acquiring the virus.
- Virus Acquisition: The virus replicates in the whitefly and becomes transmissible.
- Infection: Whiteflies transmit the virus to healthy chilli plants during feeding.
- Virus Movement: The virus moves through the plant's vascular system, causing symptoms.
- Vector Spread: Infected whiteflies transmit the virus to new plants, continuing the cycle.
Management:
- Resistant Varieties: Planting virus-resistant chilli varieties can provide effective control.
- Vector Management: Control whitefly populations with insecticides, reflective mulches, or biological control agents.
- Sanitation: Remove and destroy infected plants to reduce the virus source.
- Avoid Planting Near Infected Crops: Keep chillies away from infected crops to prevent virus spread.
- Timely Planting: Plant chillies early to avoid peak whitefly activity.
- Reflective Mulches: Use reflective mulches to repel whiteflies and disrupt their behavior.
- Insecticide Applications: Apply insecticides to manage whitefly populations if necessary.
- Physical Barriers: Use floating row covers to physically exclude whiteflies.
- Intercropping: Planting non-host crops alongside chillies can help deter whiteflies.
- Avoid Overfertilization: Excessive nitrogen can promote whitefly populations; use balanced fertilization.
- Scouting: Regularly monitor for whitefly populations and symptoms of infection.
Chilli leaf curl is a viral disease that can lead to significant yield losses if not properly managed. Implementing integrated pest management strategies, such as using resistant varieties, controlling vector populations, and practicing good crop hygiene, can help prevent and manage leaf curl in chillies effectively.
Turmeric
Turmeric, also known as Curcuma longa, is a perennial herbaceous plant that belongs to the ginger family. It is widely cultivated for its rhizomes, which are used as a spice and in traditional medicine. However, like all crops, turmeric is susceptible to a range of diseases that can impact its growth and yield.
Leaf Spot
Symptoms:
- Leaf spot in turmeric is characterized by the appearance of small to large circular or irregular spots on the leaves.
- The spots may have a brown to reddish-brown center with a yellow halo around them.
- As the disease progresses, the spots may coalesce and cause extensive damage to the foliage.
- Severe infections can lead to premature defoliation and reduced rhizome yield.
Etiology:
- Leaf spot in turmeric is caused by a fungus called Alternaria longipes.
Disease Cycle:
- Infection: Fungal spores land on the leaves and infect through natural openings or wounds.
- Colonization: The fungus colonizes the leaf tissue, leading to the formation of lesions.
- Spore Production: As the lesions mature, the fungus produces spores on the surface.
- Spore Dispersal: Wind and rain can dislodge the spores, facilitating their spread to nearby plants.
- Secondary Infections: New spores can cause secondary infections on healthy leaves.
Management:
- Cultural Practices: Maintain proper spacing between plants to improve air circulation and reduce humidity.
- Sanitation: Remove and destroy infected leaves to prevent disease spread.
- Crop Rotation: Avoid planting turmeric in the same area consecutively to reduce pathogen buildup.
- Fungicide Applications: Apply fungicides with protective and curative action according to recommended schedules.
- Resistant Varieties: If available, choose turmeric varieties with resistance to leaf spot.
- Healthy Planting Material: Use disease-free rhizomes for planting to prevent initial infection.
- Mulching: Apply organic mulch around plants to prevent soil splashing and reduce pathogen contact.
- Avoid Overhead Irrigation: Use drip irrigation to avoid wetting the foliage, which can promote disease spread.
- Monitoring: Regularly inspect plants for symptoms and take prompt action if leaf spot is detected.
Leaf spot can lead to reduced leaf area and compromised rhizome yield in turmeric. Implementing a combination of cultural practices, such as proper spacing and sanitation, along with targeted fungicide applications, can help manage leaf spot and minimize its impact on turmeric crops.
Coriander
Coriander, also known as Cilantro or Chinese Parsley, is an annual herb that is widely cultivated for its leaves, seeds, and roots. It is a popular spice crop that is used in many cuisines around the world. However, like all crops, coriander is susceptible to a range of diseases that can impact its growth and yield.
Stem gall
Symptoms:
- Stem gall disease in coriander is characterized by the development of abnormal growths or galls on the stems of the plant.
- The galls may vary in size and shape, often appearing as swollen, elongated, or distorted portions of the stem.
- The galls can range in color from green to brown or even reddish, and they may be covered with a powdery substance.
Etiology:
- Stem gall in coriander is caused by a bacterium called Pseudomonas syringae pv. coriandricola.
Disease Cycle:
- Infection: Bacteria enter the plant through natural openings or wounds.
- Colonization: The bacteria multiply and cause localized infection, leading to gall formation.
- Gall Development: As the bacteria continue to multiply, galls develop on the stem.
- Spread: Rain, wind, and mechanical activities can spread bacterial cells to nearby plants.
Management:
- Use Disease-Free Seeds: Start with certified disease-free seeds to reduce the introduction of the pathogen.
- Sanitation: Remove and destroy infected plant material to prevent further spread of the disease.
- Crop Rotation: Avoid planting coriander in the same location in consecutive seasons.
- Avoid Overhead Irrigation: Use drip irrigation to prevent water splashing and reduce disease spread.
- Fungicide Applications: Copper-based fungicides can be applied preventively to help manage bacterial diseases.
- Resistant Varieties: If available, choose coriander varieties that are less susceptible to stem gall.
- Spacing: Proper spacing between plants can improve air circulation and reduce humidity, which can inhibit disease development.
- Fertilization: Maintain proper nutrient balance to promote plant health and vigor.
- Monitoring: Regularly inspect plants for the development of galls and other symptoms.
Stem gall disease in coriander can cause deformities in stems, reduce plant health, and potentially impact yield. Implementing a combination of preventive measures, cultural practices, and fungicide applications can help manage stem gall disease and protect coriander crops.
Marigold
Marigold is a popular ornamental plant that is widely cultivated for its attractive flowers. It is a hardy plant that is relatively easy to grow, but like all plants, it is susceptible to a range of diseases that can impact its growth and appearance.
Botrytis blight
It is also known as gray mold, is a fungal disease that affects marigold plants. The disease is caused by the fungus Botrytis cinerea, which can infect all parts of the plant, including the leaves, stems, and flowers.
Symptoms:
- Botrytis blight in marigold appears as small, water-soaked spots on leaves, stems, and flowers.
- These spots enlarge and turn brown, often surrounded by a yellow halo.
- As the disease progresses, the affected tissue becomes covered with a grayish-brown fuzzy growth of fungal spores.
Etiology:
- Botrytis blight is caused by the fungus Botrytis cinerea.
Disease Cycle:
- Infection: The fungus overwinters on plant debris and in the soil. Spores are released during wet conditions.
- Spore Germination: Spores germinate on plant surfaces and penetrate the plant tissue.
- Colonization: The fungus spreads within the plant, causing lesions and decay.
- Spore Production: Under high humidity, the fungus produces grayish-brown spore masses that can be easily spread by wind or splashing water.
- Spread: Spores are carried by wind, water, or contact, and can infect other plants.
Management:
- Sanitation: Remove and destroy infected plant material to prevent overwintering of the fungus.
- Spacing: Proper spacing between plants improves air circulation, reducing humidity that favors disease development.
- Avoid Overhead Irrigation: Use drip irrigation to minimize water splashing on plant surfaces.
- Fungicide Applications: Apply fungicides at the first sign of disease to prevent its spread.
- Remove Dead Flowers: Regularly remove spent flowers to reduce potential sites for infection.
- Proper Planting: Choose well-draining soil and avoid planting in areas prone to waterlogging.
- Good Air Movement: If growing in a greenhouse, ensure adequate ventilation to reduce humidity.
- Resistant Varieties: Select marigold varieties that are less susceptible to Botrytis blight.
- Monitoring: Regularly inspect plants for symptoms and take immediate action if disease is detected.
Effective management involves a combination of cultural practices, fungicide applications, and vigilant monitoring to prevent and control the disease.
Rose
Roses are popular ornamental plants that are prized for their attractive flowers and fragrance. They are susceptible to a range of diseases that can impact their growth and appearance, but with proper management practices, these diseases can be controlled.
Dieback
Symptoms:
- Rose dieback initially appears as wilting and yellowing of leaves on individual branches.
- The affected branches may exhibit dieback, with leaves turning brown and remaining attached to the stem.
- Black cankers or lesions may develop on the stems, causing a decline in plant vigor.
- Affected canes may eventually die and can be easily snapped off.
Etiology:
- Rose dieback is caused by several fungi, including Diplocarpon rosae (black spot pathogen) and Phomopsis spp..
Disease Cycle:
- Infection: The fungus overwinters on infected canes, fallen leaves, and other plant debris.
- Spring Infection: In spring, spores are produced on infected canes and are spread by rain or splashing water.
- Spread: Rain and water splash disperse the spores to new growth, resulting in new infections.
- Lesion Development: Infected canes develop lesions that may girdle the stem, causing dieback.
- Secondary Infections: Infections can occur repeatedly during the growing season if environmental conditions are conducive.
Management:
- Pruning: Prune and destroy infected canes during the dormant season to reduce overwintering inoculum.
- Sanitation: Remove and destroy fallen leaves and debris to reduce sources of infection.
- Water Management: Avoid overhead watering to prevent water splash and leaf wetness.
- Good Air Circulation: Proper spacing and pruning promote air circulation, reducing humidity.
- Fungicide Applications: Apply fungicides preventively or as directed by a local extension office.
- Resistant Varieties: Choose rose varieties with resistance to dieback pathogens.
- Mulching: Apply a layer of organic mulch around the base of rose plants to prevent spore splash.
- Monitoring: Regularly inspect plants for symptoms and take action promptly if dieback is observed.
Rose dieback can lead to reduced plant health, decreased flower production, and overall decline of the rose plant. Proper sanitation, cultural practices, and targeted fungicide applications are essential components of managing this disease and maintaining healthy rose plants.
Powdery Mildew
- Powdery mildew on roses appears as a white to gray powdery growth on the upper leaf surfaces.
- Initially, small spots of powdery growth develop and spread to cover larger areas.
- Affected leaves may become distorted, curl, and eventually drop prematurely.
- Buds and young stems can also be infected, leading to stunted growth and deformed flowers.
Etiology:
- The powdery mildew on roses is caused by various species of fungi belonging to the Podosphaera genus.
Disease Cycle:
- Infection: The powdery mildew fungi overwinter on infected canes, buds, and other plant parts.
- Spring Infection: In spring, spores are produced in structures called conidiophores and spread by wind.
- Infection Spread: Spores land on susceptible plant parts and germinate, forming new infections.
- Secondary Infections: The fungus can produce multiple generations in a single growing season.
- Overwintering: The fungus can form resting structures that survive on infected plant debris over winter.
Management:
- Pruning: Remove and destroy infected plant parts during the dormant season.
- Sanitation: Remove fallen leaves and debris to reduce overwintering sources of infection.
- Water Management: Avoid overhead watering to minimize leaf wetness.
- Good Air Circulation: Proper spacing and pruning promote air movement and reduce humidity.
- Fungicide Applications: Apply fungicides preventively or as recommended by local experts.
- Resistant Varieties: Choose rose varieties with natural resistance to powdery mildew.
- Sulfur Dust: Application of sulfur-based products can help manage powdery mildew.
- Biological Controls: Beneficial microorganisms can help suppress powdery mildew.
- Monitoring: Regularly inspect rose plants for symptoms and signs of powdery mildew.
Powdery mildew can affect the aesthetics of roses and lead to decreased vigor and flower production. A combination of cultural practices, sanitation, and appropriate fungicide applications can effectively manage powdery mildew and promote healthy rose growth.
Black Leaf Spot
Symptoms:
- Black leaf spot on roses appears as small, circular to irregular black spots with fringed edges on the upper surface of the leaves.
- These spots can coalesce and cover larger portions of the leaf, causing yellowing and premature leaf drop.
- Severe infections can weaken the plant, reduce flowering, and lead to overall decline.
Etiology:
- Black leaf spot is caused by the fungus Diplocarpon rosae.
Disease Cycle:
- Overwintering: The fungus overwinters in infected leaves and canes.
- Spring Infection: Spores are released from infected debris in spring and are spread by splashing water.
- Infection Spread: Spores land on susceptible leaves and penetrate the leaf surface.
- Lesion Development: Infections result in the formation of characteristic black spots.
- Secondary Infections: Additional spore production can occur throughout the growing season.
- Leaf Drop: Severely infected leaves can drop prematurely.
Management:
- Sanitation: Remove and destroy fallen leaves and debris to reduce overwintering sources.
- Water Management: Avoid overhead watering to minimize leaf wetness.
- Good Air Circulation: Proper spacing and pruning promote air movement and reduce humidity.
- Fungicide Applications: Apply fungicides preventively or as recommended by local experts.
- Resistant Varieties: Choose rose varieties with natural resistance to black leaf spot.
- Pruning: Prune to improve air circulation and remove infected plant parts.
- Mulching: Apply organic mulch to prevent splashing of spores onto leaves.
- Biological Controls: Beneficial microorganisms can help suppress the disease.
- Monitoring: Regularly inspect rose plants for symptoms and signs of black leaf spot.
Black leaf spot can impact the overall health and aesthetics of rose plants. Integrated management practices, including proper sanitation, cultural practices, and appropriate fungicide applications, can help control the disease and maintain healthy roses.
Regularly inspecting your roses for signs of black spot and other diseases, and promptly treating any infections, can help keep your plants healthy and beautiful. With proper care and management, you can enjoy the beauty and fragrance of your roses for years to come.