Vegetable plant damage zaps the investment of time and money you make in your garden. Whether due to a mistake on your part or environmental factors, the potential damage to the garden ranges from decreased production to total destruction of your vegetable crop. By understanding the threats to your vegetable garden, you are able to prevent or stop damage at the first signs.
Vegetable plant diseases are usually either bacterial or fungal in nature. The extent of the damage to the plant depends on the type of disease and how early you catch it. Some diseases only affect one type of vegetable, such as asparagus rust or corn smut. Some types affect only a few vegetables. For example, bacterial blight mainly harms beans and peas. Other diseases, such as downy mildew and verticillium wilt, can spread to many different types of vegetables. Here is a list of some of the common diseases that affect vegetables:
- Downy Mildew
- Alternaria Leaf Spot
- Frogeye Leaf Spot
- White Spot fungus
- Powdery Mildew
- Blossom End Rot
- White Rust
- Bacterial Soft Rot
- Aster yellows
- Black Rot
- Root Nematode
Downy mildew is not a fungus, but a water mold (like Phytophthora and late blight). White, gray, bluish, or violet downy patches of mildew form mostly on the undersides of leaves in damp weather. Pale green to yellow or brown areas usually develop on the upper leaf surface opposite the downy growth. Affected leaves often wilt, wither, and die early. In wet or very humid conditions, the disease develops rapidly. Downy mildew can spread via air, splashing water, and on people’s tools and hands.
The best control of downy mildew is to make sure that your plants do not get it in the first place. Since downy mildew needs water to survive, the very best thing you can do to prevent downy mildew is to water your plants from below. Water that sits on the leaves of the plant gives the downy mildew a way to infect and spread on the plant.
Alternaria Leaf Spot
Alternaria leaf spot is a common foliar disease of brassica crops caused by the fungal pathogenAlternaria brassicicola. The disease can be a problem for many brassica crops including cabbage, cauliflower, kale, brussels sprouts, and broccoli. Even small infections can lead to an unmarketable crop.
The most common symptom ofAlternariadiseases is yellow, dark brown to black circular leaf spots with target like, concentric rings. Lesion centers may fall out, giving the leaf spots a shot-hole appearance. Individual spots coalesce into large necrotic areas and leaf drop can occur. Lesions can occur on petioles, stems, flowers, flower pedicels, and seed pods. Treatment for Alternaria requires fungicide to be sprayed directly on infected plants, as well as improvements in sanitation and crop rotation to prevent future outbreaks.
Frogeye leaf spot
Frogeye leaf spot is a foliar fungal disease caused by Cercopsora sojina. This fungal disease is residue borne but is also widely spread through wind from field to field. Disease development is favored by extended periods of wet weather throughout the growing season.
Symptoms of frogeye leaf spot are most visible and typically seen on leaves, but can also occur on stems, pods, and seeds. Lesions on leaves begin as small, dark, water-soaked spots. They develop into brown spots surrounded by a darker reddish-brown or purple ring.
The centers of the lesions turn light brown or light gray as they age. The center of spots may turn white with black specks visible (fungal fruiting structures) or the centers may fall away leaving a ‘shot hole’ appearance. The lesions may eventually merge, covering large areas of the leaves and resulting in defoliation.
White leaf spot
White leaf spotis a fungal disease of cruciferous vegetables (brassicas) caused by the pathogenMycosphaerella capsellae, which is also known asPseudocercosporella capsellae. The distribution of this disease pathogen is worldwide, it can be found in many countries with temperate climates, where brassicas are grown.
White spot disease gets its name from the circular white spots that are scattered over the leaves, stems, or pods of infected plants. Older spots may develop dark borders, and the centers may fall out. Such lesions look like shot holes.
In addition to turning yellow, leaves that are severely affected dry out and wither, although they remain attached to the plants. Lesions on the stems are superficial with a distinct boundary between tissue that is diseased or healthy. The lesions start out brown and then turn ash-gray to white. Large numbers of tiny dark specks form in the lesions, which are known as gray stem.
Infected seed pods start out with small brown spots. They then expand and become grayish-white with dark spots inside.
Powdery mildews are among of the most common diseases of ornamentals; many flowers, vegetables, and woody plants. This disease is caused by a fungus that attacks the plant and forms a white powdery spore on new tender growth then spreads out into other plant parts. The pathogen is usually favoured by warm, dry days and cooler, damp nights.
Even though there are several types of powdery mildew fungi, they all produce similar symptoms on plant parts. Powdery mildews are characterised by spots or patches of white to greyish, talcum-powder-like growth. Tiny, pinhead-sized, spherical fruiting structures that are first white, later yellow-brown and finally black may be present singly or in a group. These are the cleistothecia or over-seasoning bodies of the fungus.
The disease is most commonly observed on the upper sides of the leaves. It also affects the lower sides of leaves, young stems, buds, flowers and young fruit. Infected leaves may become distorted, turn yellow with small patches of green, and fall prematurely. Infected buds may fail to open.
Also Read: Different Types of Cabbage To Grow At Home
Anthracnose is a term used to loosely describe a group of related fungal diseases that typically cause dark lesions on leaves. In severe cases it may also cause sunken lesions and cankers on twigs and stems. Anthracnose affects many deciduous and evergreen trees and affect cucurbits, legumes, pepper, sweet corn, and tomato.
Symptoms on seedlings occur as wilt of cotyledons and stem lesions near the soil line when the fungus is seed borne. On mature leaves, small pale yellow, water-soaked areas emerge near veins and enlarge rapidly, turning tan to dark brown. The spots may coalesce, resulting in blighting, distortion, and death of entire leaves.
The dry, dead centers of old lesions often crack and tear, giving a ragged appearance to the foliage. Lesions on petioles and stems are elongate and slightly sunken. Young fruit may turn black and die if their pedicels are infected, while older fruit develop circular, noticeably sunken, dark-green to black lesions which may exhibit a salmon colored exudate in moist weather.
Wirestem is a disease of young vegetable brassica (cole crop) plants that affects both direct-seeded and transplanted crops. The primary symptom is dark lesions of varying depth and length on the hypocotyl (seedling stem) at or just above the soil line. Lesions often extend down the root. When wirestem is severe, the entire outer layer of the taproot rots away, leaving only the tough water-conducting tube in the center of the root. Lateral roots also rot.
Secondary aboveground symptoms associated with lesions that girdle the stem include wilting, stunting, and a blue color to the youngest leaves. Moist soil may stick to the lesions, held there by the fungal pathogen. Wirestem can occur on greenhouse-grown transplants if potting mix becomes contaminated or is mixed with infested native soil.
Wirestem can kill plants outright. Just as important, surviving plants may be stunted permanently and never produce a harvestable yield. Because of stand loss and stunted plants, wirestem reduces the number and weight of marketable-sized heads of cabbage and broccoli or collard plants per acre.
Blossom-end rot (BER)
Blossom-end rot (BER) is a common nutritional disorder of tomato, pepper, eggplant, pumpkin, squash, and watermelon that is caused by a shortage of calcium in enlarging fruits.
This nutritional disorder typically occurs when plants are growing rapidly and often affects the first developing fruits. Dark blemishes appear on the blossom-end of affected fruits as cells break down. They may enlarge until the entire bottom of the fruit becomes dark, shrunken, and leathery.
Factors that encourage blossom-end rot include low soil pH and low levels of calcium, inconsistent watering, shallow watering or droughty conditions, and excessive use of nitrogen fertilizers. Symptoms are rarely seen in cherry tomatoes and are most often seen in large plum or paste-type tomato cultivars and long pepper fruits.
Damping-off is a soil-borne fungal disease that negatively affects the vegetables and flowers in your garden, primarily targeting seeds and new seedlings. Damping-off refers to the rotting of stem and root tissues at and below the soil line. In most cases, infected plants will germinate and come up fine, but within a few days, they become water-soaked, mushy, collapse at the base and die. Damping-off commonly occurs in low-lying areas that have poor drainage and hold water.
In all cases, most damage is done to seeds and seedlings during germination and before or after emergence (pre-emergence and post-emergence damping-off, respectively.
Other symptoms of damping-off may include a failure of seeds to germinate, discoloration and rot of young stems near the soil line and wilting, collapse, and death of young seedlings. Seedlings with damping-off often have discolored and rotting roots. In high-humidity situations, white, fluffy growth of the causal pathogen may develop on infected tissues.
Plants beyond the seedling stage that are affected by damping-off pathogens are typically said to be affected by crown, root, and/or stem rots rather than damping-off, though similar symptoms may occur across all of these diseases.
Blackleg disease in vegetables can refer to a fungal pathogen that affects cole crops or bacteria that attacks potatoes. Blackleg is caused by Phoma lingam and can spread rapidly within a field. The bacteria become active when environmental conditions are right, and then disease occurs. Blackleg can occur at any time during the growing season, but it is favored cool, wet conditions at planting followed by warmer weather.
Blackleg begins as watersoaked lesions at the base of the stem. The lesions eventually coalesce and turn dark as the infection progresses up the stem. The stem pith decays and darkens, and vascular tissue in and above the lesion may be discolored. In wet weather, the decay tends to be slimy; in dry weather, stems may be hollow and desiccated. Leaves on affected stems may be wilted, chlorotic, or brown, and plants may collapse. Secondary infections may begin higher up on stems. Tubers may also rot.
In aerial stem rot, the bacteria may be present in the field in weeds or on crop debris and enter plants through wounds or leaf scars. Bacteria may also be spread by insects or splashing water.
White rust, also called white blisters, is a fungal disease caused by the fungus Albugo candida, which affects cruciferous plants. The perfect time for growing cruciferous vegetables also provides the perfect growing conditions for Albugo because the disease generally occurs when nights are cool and damp, and days are warm.
White rust, sometimes called white blister, is easily recognized by the chalk-white, cheesy, raised spore masses that occur most commonly on the underside of the leaf. The floral parts of radish, cabbage, and cauliflower seed plants are grossly deformed and sterile. Occasionally, swollen galls form in the petioles and stems of some plants and even in the roots of radish, horseradish, and a few other plants.
The leaves of systemically infected horseradish plants are usually smaller than normal and may curl inward. The first, and often overlooked, symptom of white rust is the appearance of small, irregular yellow areas on the upper leaf surface. Once spores are released, these yellowish areas die and become reddish brown to brown and may be difficult to distinguish from other diseases.
Fungicides used to treat downy mildew are sometimes effective against white rust, particularly the leafier crops. Treatment must begin at the first signs of infection. The methods for controlling white rust fungus or how to prevent white rust are largely organic.
Also Read: Major Types of Mushrooms To Grow At Home
Bacterial soft rots
Bacterial soft rots are caused by several types of bacteria, but most commonly by species of gram-negative bacteria, Erwinia, Pectobacterium, and Pseudomonas. It is a destructive disease of fruits, vegetables, and ornamentals found worldwide, and affects genera from nearly all the plant families.
Name of the disease aroused from the characteristic soft decay of fleshy tissue which terminates into watery or slimy mass. The soft rot bacterium enters plant tissues primarily through wounds, often created by insect feeding or bruising at harvest. Insects and water are effective in spreading the bacterium. The decay is aggravated when high humidity is coupled with high temperature which results in fast rate of multiplication of the pathogen. For this reason much of the loss due to this disease occurs during middle of the summer.
Symptoms of soft rot include rotted tissues that are wet, cream to tan in color, and soft. Rot begins on the tuber surface and progresses inward. Infected tissues are sharply delineated from healthy tissue by dark brown or black margins. Shallow necrotic spots on the tubers result from infections. Rotting tissue is usually odorless in the early stages of decay, but develops a foul odor as secondary organisms invade infected tissue.
An effective control bacterial soft rot can be achieved through prevention because once infection occurs, it cannot be cured, but the bacteria can be prevented from spreading. Copper-based fungicides are recommended for use in preventing and suppressing the activity of the bacterial pathogen.
Aster yellows is caused by the aster yellows phytoplasma, a bacterium-like organism (formerly called a mycoplasma-like organism), that lives in the food-conducting tissue (phloem) of plants. Insects that suck the sap of plants, especially the aster leafhopper, vector the disease.
The spread of aster yellows is worse in cool, wet summers. Hot dry weather is not favorable for either the phytoplasma or the leafhopper. As with many disease and pest problems, diagnosis is perhaps the most important factor in controlling aster yellows.
Aster yellows is primarily transmitted by leafhoppers. When a leafhopper feeds on a plant infected with aster yellows it becomes “infected” with the phytoplasma and remains infected throughout its life. The phytoplasma cells multiply and cause infection of the insect’s salivary glands within one to three weeks. When the infected insects feed on healthy plants, they inject the phytoplasma cells into the plant phloem. Susceptible plants will be symptomatic in 10 to 40 days.
Chlorosis, yellowing of the leaves while the veins remain green, is a major symptom of aster yellows. Growth slows down and leaves may be smaller and more narrow than usual. Foliage is sometimes curled. Flowers may be deformed and exhibit bizarre tufts of deformed leaves inside the flower or in place of the flower. Flowers may not produce seeds. The symptoms of the disease will often differ depending upon what species is infected. For instance, carrot roots may be bitter and hairy while lettuce may show pink or tan spots and have twisted inner leaves.
Clubroot is caused byPlasmodiophora brassicae, a fungus-like organism that does not form a true mycelium (the vegetative part of a fungus) and reproduces by resting spores. If susceptible roots are nearby, the resting spores germinate and produce zoospores. These are spores that can move around in water and infect the root hairs of susceptible plants.
Affected plants produce large distorted roots and wilting is often the first above-ground symptom. Plants which are severely infected will be stunted, produce poor quality crops and may die before harvest.
In the infected roots, the cells of the fungus-like organism grow rapidly in number and size, forming the typical abnormal club-shaped growth. During that process, new zoospores are also produced, which then infect healthy tissue of the same plant or nearby plants. In the mature clubroot-affected root tissue, new resting spores are also formed. Once the roots disintegrate, these resting spores are released into the soil.
Brassica crops vary in their susceptibility to clubroot. Chinese cabbage is very sensitive to the disease. Cauliﬂower is less susceptible but more susceptible than broccoli and head cabbage. There is also different tolerance to clubroot between varieties within each species.
Black rot, caused by the bacteriumXanthomonas campestrispv.campestris, is considered the most serious disease of crucifer crops worldwide. This disease is also known as blight, black stem, black vein, stem rot, and stump rot. Diseased plants may rot quickly before or after harvest because of secondary infection from bacterial soft-rot. All crucifer crops are susceptible to black rot; radish and kale, however, are less easily infected. The bacterium can persist in plant residue for 1-2 years or as long as the plant debris remains intact.
The plant can be infected at any time during its life cycle. On young seedlings a yellowing appears along the margin of the cotyledons, which later shrivels and drops off. On the margins of mature leaves, similar yellowing appears. Initially, a small V-shaped area develops, but as the diseased area enlarges, the veins become distinctly black. In contrast to Fusarium yellows the veins are brownish in colour. The affected stem, when cut crosswise, shows a characteristic black ring. In later stages the entire head may turn black and soft due to secondary infection by soft rot bacteria.
The bacteria survive in infected seed, in debris from diseased plants left in the field and in infested soil. Further spread is facilitated by water-splash, running water, and handling infected plants. The bacteria enter the plant mainly through water pores at the edges of leaves. They can also enter through the root system and wounds made by chewing insects.
Root-knot nematodes attack a wide variety of plants and can become serious pests in the home garden. They are microscopic roundworms that live in the soil and on plant roots. They injure plants by feeding on root cells with their needle-like mouthparts (stylets). The root system can become damaged to the point where the plant cannot properly absorb water and nutrients.
Symptoms on affected plants may be evident on parts of the plant both above and below the ground. Above the ground, plants may appear stunted and discolored and may die. Plants may wilt easily in hot, dry weather and appear to have nutrient deficiencies. Beneath the ground, the roots may have knots or galls (swollen areas) on them. Both large and small roots will have round swellings on them. The entire root system may be shallow with areas that are dead or branched excessively.