Vegetable Diseases – Types, Control In India

Vegetable Diseases and Their Control in India

Vegetables provide essential vitamins, minerals, antioxidants, and phytochemicals and are important for the food and nutritional security of the country. Some important vegetable crops grown in India are Potato, Onion, Tomato, Cucumber, Frozen Peas, Cauliflower, Cabbage, Bean, Brinjal, Garlic, and Okra. India is the second-largest producer of vegetable crops in the world (ranks next to China) and accounts for about 15% of the world’s production of vegetables. India produces approximately 163.38 million metric tonnes of vegetables from an area of 9.35 million hectares with an average productivity of 17 Mt/Ha. However, the vegetable requirement is 300g/day/person as recommended by the dietician; we can meet only around 1/9th of that requirement. In this article we also discuss below topics about vegetable diseases;

• Tips for managing fungal diseases
• Types of vegetable diseases
• Vegetable diseases and their control in India
• Diseases of vegetable crops in India
• Bacterial diseases of vegetable crops
• How do you prevent vegetable fungus
• Tips for managing bacterial vegetable diseases

A Step by Step Guide to Vegetable Diseases and their Control

Perfectly healthy vegetable crops can be affected by air, water, or soil-borne diseases at any time. Understanding the causes, identifying them early, and taking effective action will help you establish and keep a healthy vegetable garden. The vegetables are subjected to several plant pathogens like fungi, bacteria, and viruses. These pathogens are agents that cause diseases. Our warm and humid environments are conducive to the development of several diseases. Also, continuous cropping and poor agronomic practices contribute to disease development. Diseased vegetable crops are frequently expressed by the development and production of symptoms. Some common symptoms on specific parts of plants include wilting, discoloration, spotting, distortion, swelling, stunting, elongation, or rotting of plant leaves, stems, fruits, or roots.

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Vegetable diseases take their energy from the crops on which they thrive. Vegetable plant diseases are described by a variety of symptoms like moldy coatings, wilting, scabs, blotches, rusts, and rot. Some diseases occur when environmental conditions are suitable for pathogens to develop on susceptible hosts. Many types of organisms cause infectious diseases of crops, but the five major types of plant pathogens are fungi, water molds, bacteria, viruses, and nematodes. Also, adverse environmental conditions can cause non-infectious diseases of plants, which are referred to as disorders. Adverse conditions include improper soil pH level, nutrient deficiencies and toxicities, soil compaction, excess water, herbicide damage, and more. Plants weakened by adverse conditions can be further predisposed to attack by pathogens.

The vegetables farmers face many challenges which include selecting the right variety of seeds for vegetable crops such as tomato, cole crops, hot peppers, cucumbers, okra, etc., and protection from several diseases. The crop losses in the country due to several pests range from 10 to 30%. The major diseases affecting vegetable crops are damping off, late blight, early blight, leaf spot (Anthracnose, Septorial), powdery mildew, and fruit rot.

Fungal Diseases in Vegetables

Fungi constitute the largest number of plant pathogens and are responsible for different types of diseases. Most vegetable plant diseases are caused by fungi. The fungal diseases damage plants by killing cells and causing plant stress. Fungal leaf spots, which include brown, yellow, or black spots, are common on many vegetable crops.

Some fungal diseases occur on a wide range of vegetable plants. Some fungal diseases include Anthracnose, Botrytis rots, Downy mildews, Fusarium rots, Powdery mildews, Rusts, and Sclerotium rots.

Some Vegetable Diseases symptoms and Their Control

Black rot of vegetable diseases

Black rot disease is one of the most serious diseases of crucifers and it is caused by the bacteria, Xanthomonas campestris pv. campestris. It is a potentially lethal bacterial disease that affects cruciferous vegetables like broccoli, Brussels sprouts, cabbage, cauliflower, kale, and turnip, as well as cruciferous weeds like shepherd’s purse and wild mustard. The initial symptom of this disease is yellow V-shaped lesions with blackening of veins; usually develop around the leaf margin. As lesions enlarge, leaf tissues turn brown color and dry out. Sprays containing antagonistic bacteria such as Bacillus spp. can be successful in controlling black rot disease. Such sprays activate a plant’s defense system and cause the plant to put less energy into growth and crop yield.

Leaf blight of vegetable diseases

Leaf blight inflicted by the Rhizoctonia solani fungus. Leaf blight disease is common in melon, but can also affect cucumber, pumpkin, and squash. Infected plant leaves have patches of dull green or brown lesions that eventually dry out. Potatoes and tomatoes are affected by this fungal disease. Initially, leaves will shrivel and rot before the disease spreads to the fruit which will turn brown. Leaf blight thrives in warm, wet weather commonly in late summer. Early varieties will normally crop before these conditions arrive. It is good practice to rotate seed stock or to use blight resistant plant varieties. Affected plants should be destroyed and not composted.

Potato & tomato blight of vegetable diseases

Blight disease is a serious disease of potatoes and tomatoes. Blight causes discoloration of the plant leaves, turning them brown from the edges inwards. The leaves can dry and curl, though in moist conditions a white fungal growth can occur around the edges. The stems of the plants will turn brown color and in advanced cases, the plant will collapse and die. Then, carefully remove and destroy all affected parts as soon as you see them. And, a degree of protection can be achieved by preventative spraying with a suitable fungicide. Spray before symptoms occur early in the growing season or in warm and moist conditions.

Downy mildew of vegetable diseases

Downy mildew disease is caused by the fungus, Peronospora brassicae. The symptoms are irregular yellowish color spots on the upper leaf surface with corresponding brown spots on the under surface. The undersurface of leaf lesions is covered with white or grey mycelia and spores under humid conditions. Infected leaves eventually dry up.

Affects many vegetable crops and appears as a white to purple “downy” growth on the undersides of leaves and long stems. The best method to prevent downy mildew disease is to avoid the conditions that favor it. Prune plants to improve air circulation and water in the early morning to give plants time to dry out during the day. If you catch the infection early, apply copper fungicides every 7 to 10 days until harvest. Severely infected plants must be removed. If plants are grown in a greenhouse a soil irrigation system can be beneficial as it reduces the need for foliar watering and keeps the plant leaves dry.

Powdery Mildew of vegetable diseases

Powdery mildew grows as a white powdery coating over the surfaces of plant leaves. Some disease affected plants are Pea, Bean, Okra, Cucumber, Squash, Muskmelon, and Pumpkin. The first symptoms of infection occur as a superficial white coating of mycelium on older leaves. This fungus specific to each host plant displays a white powdery coating on the surface of leaves which causes plants to become distorted and growth to die back. Also, affected plants display dark brown or bright yellow color spots.

If it isn’t treated, the problem can cause vegetable plants to die or fruiting to fail. Removal and disposal of infected plant leaves and stems will help prevent the development of spores for the next season. For preventing this disease you have to select resistant cultivars. Pull up and then remove all plant debris at the end of the season. Infections start when plants are mature and are rarely a problem for gardeners. There are horticultural oil products labelled for powdery mildew control on cucurbits.

Damping-off of vegetable diseases

Fungi and water molds can attack newly planted vegetable seed (reemergence damping-off) and young seedlings (post-emergence damping-off). Prepare the beds to ensure good drainage, and do not overwater during the germination process. The use of fungicide-treated seeds will help to prevent this disease. It is caused by a variety of different soil-borne fungi causing young seedlings to rapidly fail. Plants under stress due to high-temperature levels or waterlogging are particularly prone.

Using good quality seed compost, thorough cleaning of pots and trays, and good ventilation will help to prevent this disease. Slight under watering at the seedling stage is more advisable as plants create a stronger root system searching for water and are far less likely to be troubled by this disease.

Club Root of vegetable diseases

Club root is a fungus disease and affected plants are yellowish and stunted, with large malformed ‘clubbed’ roots. Club root can be severe in warm weather. Avoid growing brassicas in the same area for 4 years and lime the soil if it is acidic. The first signs of disease infection are wilting, and a dying plant. Then, roots become swollen and distorted, restricting growth and yield. Club root disease caused by Plasmodiophora brassicae is a major disease of brassica crops worldwide. This disease occurs on broccoli, Brussels sprouts, cabbage, cauliflower, turnip, rutabaga, and radish. This disease can also infect cruciferous weeds (mustard family) as well as some genera of grasses. Alkaline soils can help to curtail, although not eliminate, the Club root disease.

Club root disease is difficult to manage and the best method to control its spread is to rotate crops. This means not planting cruciferous plants in the same area more than once every 3 or 4 years. Traditionally, Club root disease has been managed in vegetable brassicas by rotation with non-brassica crops.

Bacterial wilt of vegetable diseases

Bacterial wilt is a serious soil-borne disease of tomato and chilli plants. It is mainly caused by bacteria, Ralstonia solanacearum. The symptoms of this disease are the rapid wilting of leaves during the warmest part of the day. As the disease progresses, sudden and permanent wilt of the entire plant occurs. The lower stem and plant roots show a dark brown discoloration. There are no known effective chemical controls for bacterial wilt disease. As the plants die, the bacterial pathogen is released into the soil, so the important thing you can do to prevent the spread of bacterial wilt disease is to remove diseased plants.

Early blight of vegetable diseases

Early blight can be a serious disease on other popular vegetable plants including eggplants, peppers, and potatoes. Symptoms of early blight disease include brown and black spots on leaves that enlarge and develop rings like a target. Leaves may die. Early blight is best controlled using preventative measures and destroys infected plants by burning or burying them. Use early blight-resistant vegetable plant varieties whenever possible. Also, increase the spacing between plants to increase airflow and decrease humidity and foliage drying time. Mulch your garden with approximately 1 inch of high-quality mulch, but do not over mulch as this can lead to wet soils that can contribute to increased humidity. Finally, where the disease has been a chronic problem in plants, the use of preventative applications of a copper or chlorothalonil-containing fungicide labelled for use on vegetables may be warranted.

Anthracnose of vegetable diseases

Anthracnose is a fungal disease. Anthracnose disease affected plants include pepper, bean, tomato, eggplant, cucumber, muskmelon, pumpkin, spinach, and pea. Disease symptoms include fruits and pods with small, sunken spots. To control this disease, apply liquid copper or neem sprays before and during infection periods. Begin applications just as leaf buds break in the early spring season. In the case of severely infected crops, you’ll want to destroy them.

Remove and destroy any disease infected plants in your garden. For trees, prune out the deadwood and destroy the infected plant leaves. You can try spraying plants with a copper-based fungicide, though be careful.

Bacterial Leaf Spot of vegetable diseases

Infected plants have small and dark water-soaked spots on leaves. Bacterial leaf spot affects mainly tomatoes, peppers, and cabbage-family crops in the vegetable garden. There is no cure for plants infected with bacterial spot disease. Apply copper or sulfur-based fungicides weekly at the first sign of disease to prevent this disease from the spread. Also, limit high-nitrogen fertilizers, rotate crops, and destroy any heavily infected vegetable plants.

Wilt, Fusarium, and Verticillium of vegetable diseases

These diseases also affect a wide range of vegetables including potatoes, tomatoes, peppers, and melons. Symptoms of this disease include wilting plants and plant parts that turn yellow. Find resistant cultivars whenever possible. Soil solarization before planting may help also helpful.

Common Vegetable Diseases

Basil – downy mildew and Fusarium wilt.

Beans and peas – anthracnose, leaf spots, powdery mildew, root-knot nematode, and white mold.

Bulb vegetables (garlic, and onion, etc.) – Botrytis blight, downy mildew, leaf blights (fungal), and white rot.

Cole crops (broccoli, Brussels sprouts, cabbage, and cauliflower, etc.) – Alternaria leaf spot, black rot, and downy mildew.

Corn (sweet) – leaf blights (fungal) and rust.

Cucurbits (cucumbers, melons, and squash, etc.) – angular leaf spot, downy mildew, Phytophthora blight and fruit rot, powdery mildew, root-knot nematode, and southern blight.

Eggplant/Brinjal– leaf blights fungal disease, Phomopsis fruit rot, and southern blight.

Leafy greens (collards, lettuce, mustard, and turnip, etc.) – Alternaria leaf spot and blight, downy, and powdery mildew diseases.

Lettuce – anthracnose, bacterial spot, downy mildew, and powdery mildew.

Okra – powdery mildew, fusarium wilt, and root-knot nematode.

Peas – anthracnose, powdery mildew, and rust.

Root vegetables like beets, carrots, parsnips, and turnips, etc. – leaf spots, and root-knot nematode.

Peppers – anthracnose fruit rot, bacterial spot, Phytophthora blight, southern blight, tomato spotted wilt, and other viruses.

Spinach – downy mildew and white rust.

Tomatoes – Bacterial speck, bacterial spot, bacterial wilt, early blight and other leaf spots, leaf mold, pith necrosis, root-knot nematode, southern blight, tomato spotted wilt, and other viruses.

Successful Disease Management in Vegetables

Successful disease management in vegetables begins with the exact identification of the cause of the disease problem. Many diseases are identified based on characteristic signs and their symptoms. Prevention is the key to disease management in vegetable crops. Many foliar diseases like leaf spots and mildews are manageable once they are observed.

Integrated management strategies must be adopted to control diseases. Then, these are based upon the prevention and containment of disease spread.  The best approach to disease prevention is by using disease-free seeds or planting disease-resistant varieties.

The practice of sanitation is one of the most important methods to prevent diseases. Many infected crops are sources of disease infection as they harbor disease propagules that survive between growing seasons. The removal of infected plants and crop residues as soon as they are detected can reduce disease inoculum and slow disease spread. Crop rotation is a practice where a crop planted in an area is replanted with an unrelated crop in the following season. Many diseases especially soil-borne diseases become the main problem when the same or related crops are grown in the same area each season. Then, the avoidance of planting these crops in the same site successively reduces the chance of disease infection due to the absence of suitable hosts of the same family having similar diseases.

Solarization – It is a practice that utilizes the sun’s energy to heat the soil and reduce populations of soil pathogens, insects, and weed seeds.

Organic mulches and amendments – The addition of organic matter and soil amendments can help reduce diseases caused by pathogens living in the soil. Adding organic matter to the soil enhances soil and plant health by improving soil structure, providing plant nutrients, and sustaining beneficial soil microorganisms.

Sanitation – Sanitation includes several physical practices intended to reduce pathogen populations and prevent their spread. Do not compost plant residue from diseased plants. Also, eliminate weeds because they may harbor pathogens or serve as a host for insects that can transmit viruses and other pathogens. Frequent cleaning with soap and water followed by disinfestation with a sanitizer like diluted chlorine or rubbing alcohol of tools will help prevent the spread of pathogens.

Cultural Practices for Disease Management;

Good cultural practices like rotation, sanitation, use of drip irrigation, etc. create conditions that favor plant health. Then, good cultural practices fall into one of two categories.

Then, they will reduce the initial inoculum of the pathogen, or make the environment less favorable for disease development and spread.

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Tips That Can Help to Prevent Disease Problems in Vegetables

Below are tips that can help you preventing disease problems;

• Select disease-resistant varieties.
• Avoid planting on wet and poorly drained sites.
• Reduce the pathogen levels by crop rotation.
• Grow healthy vegetable crops by providing adequate light, water, and nutrients. Then, give each plant adequate space to ensure good air circulation and add organic matter to the garden each year.
• Keep the bare ground covered with organic mulch. The newspaper covered with straw works very well.
• Avoid watering foliage in the evening and it is best to direct water around the plant base where it can quickly reach the root zone.
• Avoid handling wet foliage.
• Harvest your vegetables before they become over-ripe.
• Cut off and discard leaves and pull up and discard entire vegetable plants that are badly infected by a disease.
• Keep weeds to a minimum and control those insect pests that are most likely to spread diseases.
• Use correct temperature levels and packing conditions during transport and storage.

Common bacterial vegetable diseases and affected crops;

Common fungal vegetable diseases and affected crops;