The following is information on current diseases in the landscape from Bob Mulrooney, Extension Plant Pathologist, UD.
This is turning out to be an exciting year for plant pathologists--diseases springing up everywhere (pun intended). Look for scab, frog-eye leafspot and cedar-apple rust (bright orange lesions) on susceptible crabapple cultivars. Frogeye or Phyllosticta leafspot on red maple, silver maple and boxelder (irregular tan spots withred-brown margins--a minor disease rarely requiring control). Anthracnose, booming due to the cool wet weather can be found on sycamore, ash (same fungus causes anthracnose on Chinese fringe tree--look for curled, deformed leaves or leaflets and brown necrotic areas), even on oak leaves in the understory (producing large brown blotches and small irregularly shaped spots). Each host has its own specific anthracnose fungus. These diseases are usually not serious enough to warrant fungicide control.
Showing posts with label plant disease. Show all posts
Showing posts with label plant disease. Show all posts
Friday, May 22, 2009
Saturday, May 2, 2009
Landscape - Volutella Blight on Pachysandra
The following is information on Volutella blight of Pachysandra, a common disease of this plant in Delaware.
Volutella blight on Pachysandra has been diagnosed on old infected stems in beds exposed to full sun recently. During periods of wet weather the infected stems produce masses of salmon-colored spores that infect more stems and leaves. Prune out the blighted stems and fertilize beds with a ½ lb of nitrogen/1000 sq ft to help them recover. Fungicides are not likely to provide any control at this point, but several are labeled (mancozeb and others) if you want to try using fungicides.
Volutella blight on Pachysandra causing dieback. Photo by Jody Fetzer, New York Botanical Garden, Bugwood.org.
Information from Bob Mulrooney, Extension Plant Pathologist, UD.
Volutella blight on Pachysandra has been diagnosed on old infected stems in beds exposed to full sun recently. During periods of wet weather the infected stems produce masses of salmon-colored spores that infect more stems and leaves. Prune out the blighted stems and fertilize beds with a ½ lb of nitrogen/1000 sq ft to help them recover. Fungicides are not likely to provide any control at this point, but several are labeled (mancozeb and others) if you want to try using fungicides.
Volutella blight on Pachysandra causing dieback. Photo by Jody Fetzer, New York Botanical Garden, Bugwood.org.Information from Bob Mulrooney, Extension Plant Pathologist, UD.
Thursday, May 29, 2008
Nursery, Landscape, and Turf - Moisture and Diseases
Moist conditions favor disease development in landscape plants. The following is an article on the subject.
In Mid-May, there were days with persistent rain, mist, fog, and humid, overcast weather in many parts of Delaware. Wet weather increases disease pressure for most foliar fungal and bacterial diseases of plants in the garden and landscape. Many fungal pathogens require free moisture on the host plant surface for germination of their spores. The longer it is that leaves remain continuously wet, the better chance it is that fungal spores on the host will succeed in infecting the host plant. At average temperatures of 60-65 F, the apple scab fungus needs 9 consecutive hours of wet leaves for successful infection, the grape black rot fungus needs 8-9 hours, the rose black spot fungus needs 7 hours, shade tree anthracnose fungi need 6-12 hours, and the cedar-apple rust fungus needs only 3-4 hours. Following infection promoted by wet weather, disease symptoms typically appear on the plant a week or two later.
The two other components of the plant disease triangle, the susceptible host and the virulent pathogen are needed for a disease outbreak. For example, diseases such as apple scab, oak anthracnose, cedar-apple rust, and rose black spot are already present on susceptible host plants in many landscapes. These infections occurred during wet periods this past month. Depending on where susceptible plants are located, recent disease-favorable wetness periods have lasted anywhere from 9 hours in one day to 45 consecutive hours over two or three days. Thus, for the rest of this spring and even into summer, expect these infections to produce symptoms and more spores to continue the cycle of disease every time a prolonged wet period occurs.
Adapted from COMPLETING THE PLANT DISEASE TRIANGLE - DISEASE-FAVORABLE ENVIRONMENT By John Hartman in the May 19 edition of the Kentucky Pest News from the University of Kentucky, College of Agriculture.
In Mid-May, there were days with persistent rain, mist, fog, and humid, overcast weather in many parts of Delaware. Wet weather increases disease pressure for most foliar fungal and bacterial diseases of plants in the garden and landscape. Many fungal pathogens require free moisture on the host plant surface for germination of their spores. The longer it is that leaves remain continuously wet, the better chance it is that fungal spores on the host will succeed in infecting the host plant. At average temperatures of 60-65 F, the apple scab fungus needs 9 consecutive hours of wet leaves for successful infection, the grape black rot fungus needs 8-9 hours, the rose black spot fungus needs 7 hours, shade tree anthracnose fungi need 6-12 hours, and the cedar-apple rust fungus needs only 3-4 hours. Following infection promoted by wet weather, disease symptoms typically appear on the plant a week or two later.
The two other components of the plant disease triangle, the susceptible host and the virulent pathogen are needed for a disease outbreak. For example, diseases such as apple scab, oak anthracnose, cedar-apple rust, and rose black spot are already present on susceptible host plants in many landscapes. These infections occurred during wet periods this past month. Depending on where susceptible plants are located, recent disease-favorable wetness periods have lasted anywhere from 9 hours in one day to 45 consecutive hours over two or three days. Thus, for the rest of this spring and even into summer, expect these infections to produce symptoms and more spores to continue the cycle of disease every time a prolonged wet period occurs.
Adapted from COMPLETING THE PLANT DISEASE TRIANGLE - DISEASE-FAVORABLE ENVIRONMENT By John Hartman in the May 19 edition of the Kentucky Pest News from the University of Kentucky, College of Agriculture.
Thursday, March 27, 2008
Landscape - Plant Disease Free Material
One of the basic rules of disease control in the landscape is to plant disease free material. The following is an article on the subject.
This is the time of year when Delaware landscapers will be planting trees, shrubs, perennials, and annuals for color. Landscape introductions carry the risk of introducing new disease-causing pathogens. Landscapers, knowing that plant disease will not occur if the plant and the pathogen can be kept apart will want to consider using the principle of exclusion for disease control.
Normally, when exclusion for plant disease control is considered, we think of quarantines and inspections to keep new diseases from entering a state or nation. Currently, Delaware and other states in the eastern U.S. are excluding Phytophthora ramorum, cause of sudden oak death, by inspections of nursery plants moving from the West Coast where the disease occurs, to the East. Similarly, through exclusion, Ralstonia solanacearum race 3 biovar 2, a devastating disease of potato and other crops, is prevented from entering the U.S. on geraniums or other transplants. We can only imagine what our Eastern U.S. forests or urban streets would look like if chestnut blight or Dutch elm disease had been excluded.
On a much smaller scale, although a landscape disease may be widespread in Delaware, it doesn't mean that every site harbors the pathogen. In order to keep the site free of some plant pathogens, it becomes the responsibility of the landscaper to exclude diseases that might be damaging to plants. This means landscapers need to undertake careful inspections of incoming plants and reject those that don't meet good health standards.
Some examples might include:
Black root rot, caused by the fungus Thielaviopsis basicola, may be present on roots of holly, petunia, pansy, impatiens, geranium and other transplants. The fungus is not already present in most soils, but once introduced, will persist in the soil for many years. The tops of the plants may not show symptoms in the nursery or garden center so in order to find the disease, the plants must be knocked out of the pots and the roots examined. Inspect plants carefully and reject those with dark root lesions or blackened root tips. Once planted in the garden, these plants will decline and grow poorly.
Geranium bacterial blight, caused by the bacterium Xanthomonas campestris pv. pelargonii can devaste geraniums grown in outdoor beds. This disease is sometimes introduced into the landscape via infected transplants. On leaves, look for brown spots, often with yellow margins or check for sunken cankers on the stems. If these symptoms are observed, reject the plants because once the pathogen is introduced into the landscape, that bed can become contaminated and provide a source of infection for future geranium plants grown in the same bed. Examine geranium plants carefully and exclude any that have symptoms of leaf spot or stem cankers.
Viruses such as Impatiens Necrotic Spot Virus and many others can be carried on transplants. Most commercial transplants are free of this disease, however, we do see it from time to time on greenhouse and nursery grown annuals and perennials. Virus symptoms on transplants include deformed leaves, spotting, and yellow mosaic patterns on the leaves. Be wary of transplants with virus symptoms; exclude them from the landscape.
For a healthier landscape, remember to use the principle of exclusion to reduce the chances of introducing a pathogen that causes a plant disease that will be regretted later in the season or in the coming years.
Modified from AN EXCLUSIONARY PRINCIPLE FOR THE GARDEN By John Hartman in the March 24, 2008 edition of the Kentucky Pest News from the University of Kentucky, College of Agriculture.
This is the time of year when Delaware landscapers will be planting trees, shrubs, perennials, and annuals for color. Landscape introductions carry the risk of introducing new disease-causing pathogens. Landscapers, knowing that plant disease will not occur if the plant and the pathogen can be kept apart will want to consider using the principle of exclusion for disease control.
Normally, when exclusion for plant disease control is considered, we think of quarantines and inspections to keep new diseases from entering a state or nation. Currently, Delaware and other states in the eastern U.S. are excluding Phytophthora ramorum, cause of sudden oak death, by inspections of nursery plants moving from the West Coast where the disease occurs, to the East. Similarly, through exclusion, Ralstonia solanacearum race 3 biovar 2, a devastating disease of potato and other crops, is prevented from entering the U.S. on geraniums or other transplants. We can only imagine what our Eastern U.S. forests or urban streets would look like if chestnut blight or Dutch elm disease had been excluded.
On a much smaller scale, although a landscape disease may be widespread in Delaware, it doesn't mean that every site harbors the pathogen. In order to keep the site free of some plant pathogens, it becomes the responsibility of the landscaper to exclude diseases that might be damaging to plants. This means landscapers need to undertake careful inspections of incoming plants and reject those that don't meet good health standards.
Some examples might include:
Black root rot, caused by the fungus Thielaviopsis basicola, may be present on roots of holly, petunia, pansy, impatiens, geranium and other transplants. The fungus is not already present in most soils, but once introduced, will persist in the soil for many years. The tops of the plants may not show symptoms in the nursery or garden center so in order to find the disease, the plants must be knocked out of the pots and the roots examined. Inspect plants carefully and reject those with dark root lesions or blackened root tips. Once planted in the garden, these plants will decline and grow poorly.
Geranium bacterial blight, caused by the bacterium Xanthomonas campestris pv. pelargonii can devaste geraniums grown in outdoor beds. This disease is sometimes introduced into the landscape via infected transplants. On leaves, look for brown spots, often with yellow margins or check for sunken cankers on the stems. If these symptoms are observed, reject the plants because once the pathogen is introduced into the landscape, that bed can become contaminated and provide a source of infection for future geranium plants grown in the same bed. Examine geranium plants carefully and exclude any that have symptoms of leaf spot or stem cankers.
Viruses such as Impatiens Necrotic Spot Virus and many others can be carried on transplants. Most commercial transplants are free of this disease, however, we do see it from time to time on greenhouse and nursery grown annuals and perennials. Virus symptoms on transplants include deformed leaves, spotting, and yellow mosaic patterns on the leaves. Be wary of transplants with virus symptoms; exclude them from the landscape.
For a healthier landscape, remember to use the principle of exclusion to reduce the chances of introducing a pathogen that causes a plant disease that will be regretted later in the season or in the coming years.
Modified from AN EXCLUSIONARY PRINCIPLE FOR THE GARDEN By John Hartman in the March 24, 2008 edition of the Kentucky Pest News from the University of Kentucky, College of Agriculture.
Tuesday, March 18, 2008
Landscape - Diseases and Disease Control
The following is an article on diseases and disease control in the landscape by Bob Mulrooney, UD Extension Plant Pathologist.
Under Delaware conditions foliage diseases of trees and shrubs rarely threaten plant health but are unsightly and reduce the aesthetic value of our ornamentals. Repeated defoliation or high levels of infected foliage can reduce growth and weaken plants. This stress can make them more susceptible to insect pests or adverse weather such as drought. So disease control may be needed even if the plant is not in immediate danger. Each disease situation should be evaluated for the importance of the host plant in the landscape, the threat to plant health that it poses, and the acceptable level of plant damage or infection. Keep records of disease outbreaks. Record keeping allows the plant owner to establish a history, which indicates patterns and establishes priorities in making disease control decisions. If foliage disease control is warranted, consider replacing the plant with a resistant cultivar if available, e.g. crabapples resistant to scab; or apply a fungicide. Sometimes replacing the plant with one that has fewer pest problems is the best solution. When fungicides are needed, apply before disease symptoms appear. Prevention is the key to control with fungicides and bactericides. For trees and shrubs, most infections occur during wet, warm spring weather so the first fungicide control spray is generally aimed at bud-break and repeated 10-14 days later. Be sure to check the product label for timing and rates. Often when I report that a certain disease has been found in the landscape, the opportunity for chemical control is past. Remember three factors must be present in order to have a disease 1) a susceptible host plant 2) a disease causing organism (pathogen) and 3) suitable weather conditions for infection. If you can affect one or more of the legs of this disease triangle you can eliminate or reduce diseases in the landscape.
Written by Bob Mulrooney, Extension Plant Pathologist in a past issue of the Ornamentals Hotline.
Under Delaware conditions foliage diseases of trees and shrubs rarely threaten plant health but are unsightly and reduce the aesthetic value of our ornamentals. Repeated defoliation or high levels of infected foliage can reduce growth and weaken plants. This stress can make them more susceptible to insect pests or adverse weather such as drought. So disease control may be needed even if the plant is not in immediate danger. Each disease situation should be evaluated for the importance of the host plant in the landscape, the threat to plant health that it poses, and the acceptable level of plant damage or infection. Keep records of disease outbreaks. Record keeping allows the plant owner to establish a history, which indicates patterns and establishes priorities in making disease control decisions. If foliage disease control is warranted, consider replacing the plant with a resistant cultivar if available, e.g. crabapples resistant to scab; or apply a fungicide. Sometimes replacing the plant with one that has fewer pest problems is the best solution. When fungicides are needed, apply before disease symptoms appear. Prevention is the key to control with fungicides and bactericides. For trees and shrubs, most infections occur during wet, warm spring weather so the first fungicide control spray is generally aimed at bud-break and repeated 10-14 days later. Be sure to check the product label for timing and rates. Often when I report that a certain disease has been found in the landscape, the opportunity for chemical control is past. Remember three factors must be present in order to have a disease 1) a susceptible host plant 2) a disease causing organism (pathogen) and 3) suitable weather conditions for infection. If you can affect one or more of the legs of this disease triangle you can eliminate or reduce diseases in the landscape.
Written by Bob Mulrooney, Extension Plant Pathologist in a past issue of the Ornamentals Hotline.
Tuesday, January 29, 2008
Landscape - Recognizing Diseases on Perennials and Annuals in the Landscape
The following are some tips on recognizing diseases on perennials and annuals in the landscape.
Infectious plant diseases in the landscape are caused by pathogenic microbes such as fungi, bacteria, phytoplasmas, and viruses. Symptoms such as wilt, leaf spot, root rot, canker, and blight resulting from microbial infections represent the plant's reaction to disease. When evidence of the pathogen such as fungal spores or mycelium, bacterial ooze, or fungal fruiting bodies can be seen, they are regarded as signs of disease. Foliar diseases of landscape plants are most noticeable and they can often be identified by symptoms seen by the unaided eye and signs visible with a hand lens.
Rust diseases.
Rust diseases often produce raised pustules on the leaf surface which produce spores which are distinctively brown, reddish brown, orange or yellow in color. Infected leaves often produce a yellow spot with pustules that are found on the undersides of infected leaves. Rust diseases are favored during wet weather with moderate temperatures. Heavily infected leaves become yellow, then turn brown and die. In Delaware landscapes, rust can commonly be found on aster, daisy, dragonroot, geranium, hollyhock, jack-in-the-pulpit, rudbeckia, snapdragon, and sunflower.
Leaf spot diseases.
Leaf spots caused by fungi or bacteria are common on annuals and perennials. Symptoms vary depending on the host and the pathogen, but common leaf spot forms include angular brown or gray spots, brown spots with yellow halos, irregular blotches, tan or gray spots with reddish margins, reddish streaks and target-shaped circular spots. Some of the spots may contain tiny black pimple-like fungal fruiting structures called pycnidia. These pycnidia, as seen with a hand lens, are visible signs of disease. Spots may coalesce and blight affected leaves and heavily spotted leaves usually shrivel up and die or drop from the plant. Fungal leaf spot diseases are favored by wet, rainy seasons or frequent overhead irrigation. Examples of leaf spot of annuals and perennials include:
Alternaria fungus leaf spot on impatiens, marigold, rudbeckia, sunflower, and zinnia.
Fungal leaf streak, sometimes confused with rust, occurs on daylily.
Reddish leaf petiole streaks on peony are symptoms of Cladosporium infections.
Rose black spot is the most common defoliating disease of roses.
Iris is subject to a fungal and a bacterial leaf spot, both of which produce a gray spot with yellow halo.
Bacterial and fungal leaf spots also affect English ivy.
Begonia, chrysanthemum, and zinnia are subject to bacterial leaf spot.
Geranium bacterial blight begins as a leaf spot.
Foliar nematodes, common on shade-grown plants, cause angular spots on brunnera and heuchera, irregular blotches on anemone and salvia, and wedge-shaped dead patches on hosta. Signs of foliar nematodes may be glimpsed in leaf water droplets with a good hand lens.
Powdery mildew.
Signs of the powdery mildew fungus can be seen first as small patches and spreading to cover leaves, petioles, flowers, and stems of infected plants. These signs consist of a whitish or grayish mat of fungal mycelium, conidiospores, and conidiophores which bear the spores. Infected leaves may be twisted, curled, and distorted while covered with fungal signs. In some cases, fungal signs are sparse and leaves develop reddish splotches or take on a yellowish cast. In the landscape, powdery mildew especially affects begonia, chrysanthemum, columbine, monarda, phlox, rhododendron, rose, sedum, and zinnia. Powdery mildew does not require periods of rain or dew to thrive; warm weather and high humidity favor the disease.
Downy mildew.
Yellow patches are often observed on the upper surface of leaves infected with downy mildew. On the leaf underside, the fungus produces a whitish or grayish fuzzy fungal growth consisting of sporangial stalks and sporangia, best seen in early morning while the leaves are still moist. On rose, symptoms include dark, angular spots which produce fungal signs on the leaf undersides. Infected leaves shrivel up and die. Downy mildew can be found on alyssum, ornamental tobacco, pansy, rose, salvia, and snapdragon.
Botrytis blight.
When Botrytis blight (gray mold) is active, flowers are often attacked and blighted flowers may have dead, tan spots or blotches, or turn completely brown. Botrytis also causes tan to brown leaf spots and shoot blights, especially during cloudy, cool, moist weather. When the disease is active, signs of disease appear on dead tissues as gray or tan moldy growth of the causal fungus. Under moist conditions, almost all annuals and perennials can be affected by gray mold.
Virus diseases.
Plant virus symptoms appear commonly on the foliage, but plants are typically systemically infected. Rose mosaic virus symptoms can be seen as patterns of yellow and light-green lines, splotches, or speckles on infected leaves. Yellow or brown ring spots can be one symptom of impatiens necrotic spot virus (INSV) on New Guinea impatiens. INSV and its close relative, tomato spotted wilt virus, can also cause malformed strap-shaped leaves and stunting. During recent years, unusual virus diseases of landscape perennials such as anemone, hosta, and peony have appeared in the U.K. Plant Disease Diagnostic Laboratory with symptoms of ring spots, chlorotic spots, and mottled leaves.
Adapted from "RECOGNIZING FOLIAR DISEASES OF LANDSCAPE ANNUALS AND PERENNIALS" By John Hartman in the February 6, 2006 edition of the Kentucky Pest News form the College of Agriculture, University of Kentucky.
Infectious plant diseases in the landscape are caused by pathogenic microbes such as fungi, bacteria, phytoplasmas, and viruses. Symptoms such as wilt, leaf spot, root rot, canker, and blight resulting from microbial infections represent the plant's reaction to disease. When evidence of the pathogen such as fungal spores or mycelium, bacterial ooze, or fungal fruiting bodies can be seen, they are regarded as signs of disease. Foliar diseases of landscape plants are most noticeable and they can often be identified by symptoms seen by the unaided eye and signs visible with a hand lens.
Rust diseases.
Rust diseases often produce raised pustules on the leaf surface which produce spores which are distinctively brown, reddish brown, orange or yellow in color. Infected leaves often produce a yellow spot with pustules that are found on the undersides of infected leaves. Rust diseases are favored during wet weather with moderate temperatures. Heavily infected leaves become yellow, then turn brown and die. In Delaware landscapes, rust can commonly be found on aster, daisy, dragonroot, geranium, hollyhock, jack-in-the-pulpit, rudbeckia, snapdragon, and sunflower.
Leaf spot diseases.
Leaf spots caused by fungi or bacteria are common on annuals and perennials. Symptoms vary depending on the host and the pathogen, but common leaf spot forms include angular brown or gray spots, brown spots with yellow halos, irregular blotches, tan or gray spots with reddish margins, reddish streaks and target-shaped circular spots. Some of the spots may contain tiny black pimple-like fungal fruiting structures called pycnidia. These pycnidia, as seen with a hand lens, are visible signs of disease. Spots may coalesce and blight affected leaves and heavily spotted leaves usually shrivel up and die or drop from the plant. Fungal leaf spot diseases are favored by wet, rainy seasons or frequent overhead irrigation. Examples of leaf spot of annuals and perennials include:
Alternaria fungus leaf spot on impatiens, marigold, rudbeckia, sunflower, and zinnia.
Fungal leaf streak, sometimes confused with rust, occurs on daylily.
Reddish leaf petiole streaks on peony are symptoms of Cladosporium infections.
Rose black spot is the most common defoliating disease of roses.
Iris is subject to a fungal and a bacterial leaf spot, both of which produce a gray spot with yellow halo.
Bacterial and fungal leaf spots also affect English ivy.
Begonia, chrysanthemum, and zinnia are subject to bacterial leaf spot.
Geranium bacterial blight begins as a leaf spot.
Foliar nematodes, common on shade-grown plants, cause angular spots on brunnera and heuchera, irregular blotches on anemone and salvia, and wedge-shaped dead patches on hosta. Signs of foliar nematodes may be glimpsed in leaf water droplets with a good hand lens.
Powdery mildew.
Signs of the powdery mildew fungus can be seen first as small patches and spreading to cover leaves, petioles, flowers, and stems of infected plants. These signs consist of a whitish or grayish mat of fungal mycelium, conidiospores, and conidiophores which bear the spores. Infected leaves may be twisted, curled, and distorted while covered with fungal signs. In some cases, fungal signs are sparse and leaves develop reddish splotches or take on a yellowish cast. In the landscape, powdery mildew especially affects begonia, chrysanthemum, columbine, monarda, phlox, rhododendron, rose, sedum, and zinnia. Powdery mildew does not require periods of rain or dew to thrive; warm weather and high humidity favor the disease.
Downy mildew.
Yellow patches are often observed on the upper surface of leaves infected with downy mildew. On the leaf underside, the fungus produces a whitish or grayish fuzzy fungal growth consisting of sporangial stalks and sporangia, best seen in early morning while the leaves are still moist. On rose, symptoms include dark, angular spots which produce fungal signs on the leaf undersides. Infected leaves shrivel up and die. Downy mildew can be found on alyssum, ornamental tobacco, pansy, rose, salvia, and snapdragon.
Botrytis blight.
When Botrytis blight (gray mold) is active, flowers are often attacked and blighted flowers may have dead, tan spots or blotches, or turn completely brown. Botrytis also causes tan to brown leaf spots and shoot blights, especially during cloudy, cool, moist weather. When the disease is active, signs of disease appear on dead tissues as gray or tan moldy growth of the causal fungus. Under moist conditions, almost all annuals and perennials can be affected by gray mold.
Virus diseases.
Plant virus symptoms appear commonly on the foliage, but plants are typically systemically infected. Rose mosaic virus symptoms can be seen as patterns of yellow and light-green lines, splotches, or speckles on infected leaves. Yellow or brown ring spots can be one symptom of impatiens necrotic spot virus (INSV) on New Guinea impatiens. INSV and its close relative, tomato spotted wilt virus, can also cause malformed strap-shaped leaves and stunting. During recent years, unusual virus diseases of landscape perennials such as anemone, hosta, and peony have appeared in the U.K. Plant Disease Diagnostic Laboratory with symptoms of ring spots, chlorotic spots, and mottled leaves.
Adapted from "RECOGNIZING FOLIAR DISEASES OF LANDSCAPE ANNUALS AND PERENNIALS" By John Hartman in the February 6, 2006 edition of the Kentucky Pest News form the College of Agriculture, University of Kentucky.
Monday, November 5, 2007
Diseases - How Plants Defend Themselves Against Diseases
One of the issues with plant diseases during and following a drought year is that there is reduced resistance to plant diseases due to reduced plant defences. The following is a list of the different ways plants defend against disease.
How plants defend themselves against diseases
Constitutive (passive) plant defenses
Structural
- bark
- bud scales
- collenchyma/sclerenchyma (protect vascular bundles)
- defense trichomes (hairs)
- position, size, and shape of stomata on lower leaf surface
- the suberized outer layers of bulbs, corms, and tubers
- waxy cuticle
- suberin (similar to waxy cuticle) on primary roots (however, root hairs and root apical meristems are extremely vulnerable to attack)
Chemical (these are secondary metabolites, which are not necessary for growth of the plant)
- cyanogenic glucosides (cyanide bound to sugar molecules)
- phenolic glucosides (phenols bound to sugar molecules)
Induced (active) plant defenses
Structural
- abscission layers (infected portions of leaves drop out and block further invasion of the pathogen)
- cork layers (block further invasion of the pathogen)
- gums or resins (create barriers against invading pathogens in wounds or vascular tissue)
- papillae of callose (thickenings that prevent entry of a pathogen into a cell)
- thickening or lignification of cell walls
- tyloses
Chemical
- pathogenesis-related (PR) proteins (enzymes and other proteins produced as defense compounds)
- phytoalexins (defense compounds toxic specifically to the pathogens of the host plant)
Information from "The Relationship of Plant Stress to Plant Disease" by Ann B. Gould, Ph.D., Specialist in Plant Pathology, Rutgers University in the May 31, 2007 issue of the Plant and Pest Advisory, Landscape, Nursery, and Turf edition.
How plants defend themselves against diseases
Constitutive (passive) plant defenses
Structural
- bark
- bud scales
- collenchyma/sclerenchyma (protect vascular bundles)
- defense trichomes (hairs)
- position, size, and shape of stomata on lower leaf surface
- the suberized outer layers of bulbs, corms, and tubers
- waxy cuticle
- suberin (similar to waxy cuticle) on primary roots (however, root hairs and root apical meristems are extremely vulnerable to attack)
Chemical (these are secondary metabolites, which are not necessary for growth of the plant)
- cyanogenic glucosides (cyanide bound to sugar molecules)
- phenolic glucosides (phenols bound to sugar molecules)
Induced (active) plant defenses
Structural
- abscission layers (infected portions of leaves drop out and block further invasion of the pathogen)
- cork layers (block further invasion of the pathogen)
- gums or resins (create barriers against invading pathogens in wounds or vascular tissue)
- papillae of callose (thickenings that prevent entry of a pathogen into a cell)
- thickening or lignification of cell walls
- tyloses
Chemical
- pathogenesis-related (PR) proteins (enzymes and other proteins produced as defense compounds)
- phytoalexins (defense compounds toxic specifically to the pathogens of the host plant)
Information from "The Relationship of Plant Stress to Plant Disease" by Ann B. Gould, Ph.D., Specialist in Plant Pathology, Rutgers University in the May 31, 2007 issue of the Plant and Pest Advisory, Landscape, Nursery, and Turf edition.
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