Leaf spot

Last updated
Leaf spot
'Cercospora capsici.jpg
Leaf spot caused by Cercospora capsici
Causal agents Fungi or bacteria
HostsPlants

A leaf spot is a limited, discoloured, diseased area of a leaf that is caused by fungal, bacterial or viral plant diseases, or by injuries from nematodes, insects, environmental factors, toxicity or herbicides. These discoloured spots or lesions often have a centre of necrosis (cell death). [1] Symptoms can overlap across causal agents, however differing signs and symptoms of certain pathogens can lead to the diagnosis of the type of leaf spot disease. Prolonged wet and humid conditions promote leaf spot disease and most pathogens are spread by wind, splashing rain or irrigation that carry the disease to other leaves. [2]

Contents

Description

Leaf spots are a type of plant disease that are usually caused by pathogens and sometimes other cases such as herbicide injuries. [3] Leaf spots can vary in size, shape, and color depending on the age and type of the cause or pathogen. Plants, shrubs and trees are weakened by the spots on the leaves as they reduce available foliar space for photosynthesis. Other forms of leaf spot diseases include leaf rust, downy mildew and blights. [4] Although leaf spot diseases can affect a small percentage of the host's leaves, more severe consequences of leaf spot disease results in moderate to complete loss of leaves. [4]

Causes

The causes of leaf spots are mainly from fungi, bacteria, and viruses. However leaf spots may also be caused by abiotic factors such as environmental conditions, toxicities and herbicide injuries. [5] Foliar nematodes are another cause of leaf spots where the saliva injected into the cell walls during feeding results in the affected cells to discolour and become lesions. [6] Aphelenchoides are common foliar nematodes which produce angular leaf spots. The Aphelenchoides ritzemabosi affects chrysanthemum and other plants such as dry beans and bird's nest fern, and the Aphelenchoides fragariae affects strawberry and other ornamentals ferns. [6] [7]

Fungi

Foliar diseases such as leaf spots are commonly caused by ascomycetes and so-called deuteromycetes (mitosporic fungi). [7]

Common Ascomycetes that cause leaf spot disease: [7] [8] [9]
AscomycetesCause and Host
Cochliobolus Leaf spot on most grasses, and cereals.
Blumeriella (Higginsia) Leaf spot on cherries and plums.
Magnaporthe, M. grisea Grey leaf spot of cereals and turf grasses.
Elytroderma deformansLeaf spot of pines.
Mycosphaerella fragariae Leaf spot of strawberry.
Pseudopeziza Leaf spot of alfafa and clovers.
Pyrenophora Leaf spot on many cereals and grasses.
Cercospora Reddish lesions at first then enlarges and becomes white to light brown in the centre. Circular and varying in size.

Can appear concentric with red margins.

Leaf spot on most cereals and grasses, field crops, vegetables, ornamentals, and trees.

Myrothecium roridum Target-like spots with light brown centres and dark circumference on Gardenia augusta,

New Guinea Impatiens, Begonia species, and Gloxinia, and pansy. Distinctive dark green

and black spore producing bodies edged by white hyphae occurs in lesions.

Common Deuteromycetes that cause leaf spot disease: [7] [8] [9]
DeuteromycetesCause and Host
Alternaria Small water-soaked lesions, maturing into sunken and brown spots with or without a yellow halo.

May show concentric rings with purple margins. Necrotic tissue may fall out to appear shot-holed.

Leaf spot on many plants and crops.

Septoria Small brown spots, that turns light tan to white in the centre. Leaf spot on many crops
Bipolaris Leaf spot on grasses
Drechslera Leaf spot on grasses
Exserohilium Leaf spot on grasses
Curvularia Leaf spot on grasses
Cylindrosporium Leaf spot on many plants
Colletotrichum,

Gloeosporium (anthracnose)

Brown and necrotic spots on many plants including Anemone coronaria,

Begonia species, Dahlia hybrids, Poinsettia, Gardenia augusta, Hibiscus, geranium.

Bacteria

The most common cause of bacterial leaf spots are by bacteria in the genera Pseudomonas and Xanthomonas. For example, Pseudomonas syringae pv. tabaci is known to cause angular leaf spots of cucumber, Pseudomonas syringae pv. phaseolicola to cause bean leaf spot and Xanthomonas campestris pv. phaseoli, angular leaf spot of cotton. [7]

Virus

Whilst other pathogenic causes such as fungi and bacteria induce leaf spot disease by way of enzymes, toxins and spores, virus infections affect the host by means of synthesising new proteins that are biologically active substances such as enzymes which may sabotage the metabolism of the host. Viruses can inhibit chlorophyll development in leaves and the lack of photosynthetic activity can cause yellowing and chlorosis. Viruses inducing low levels of carbohydrates in plant tissues can result in mosaic diseases. Viral leaf spot diseases include the Apple chlorotic leaf-spot virus from the genus Trichovirus, Tospoviruses, and Coconut cadang-cadang viroid. [7]

Herbicide

Leaf spots may also be from injuries made by herbicides coming in contact with the plant. A low rate of contact from nitrile and pyridazine herbicides, can result in spotting or speckling of the plant's foliage. Diphenylether herbicides can result in reddish-colour spots shortly after application. [3] Accurate identification of leaf spot disease is needed as to distinguish signs of illness from damage done by herbicides. [10]

Symptoms

Fungi

Leaf spots caused by fungi occur due to the necrosis of plant tissues. These necrotic lesions, localised in area and shape, consist of dead and collapsed cells of the host leaves. [1] One distinct feature of fungal infections is that there may be visible spores in the centre of leaf spots. [7] Fungal leaf spots often have a brown, black, tan or reddish centre with a darker margin and vary in size. [11]

Bacteria

Bacterial leaf spot caused by Pseudomonas cichorii on a hibiscus leaf Hibiscus Bacterial leaf spot caused by Pseudomonas cichorii (5684575818).jpg
Bacterial leaf spot caused by Pseudomonas cichorii on a hibiscus leaf

Bacterial leaf spots show as necrotic, circular or angular lesions and may have a yellowish outline or halo [7] Early symptoms of bacterial leaf spots show on older leaves and lesions appear water-soaked. [12] Bacterial spots affecting dicytyledounous plants that have net-like leaf veins sometimes take a more angular shape as they are restricted by the large leaf veins. Bacterial spots on monocotyledonous plants with parallel leaf veins have a streak or striped appearance. [7] The most obvious symptom of bacterial leaf spots are the blackening of the spots after infection. Eventually older lesions dry out and become papery in texture. [12] Bacterial spots can also produce white, yellow, light cream or silver bacterial exudate depending on the type of bacteria, which may ooze from splitting lesions and/or from the underside of the spots. [7]

Bacterial leaf spots caused by Pseudomonas show red-brown spots which can distort the infected leaves, whilst those caused by Xanthomonas are angular or circular in shape outlined with a yellow halo. [13]

Virus

Leaf spots are visible symptoms of virus infections on plants, and are referred to as systemic symptoms. [7] In systematic virus infections leaf spots caused by viruses show a loss of green colour in leaves, due to chlorosis which is a repression of chlorophyll development. [1] Leaves may yellow and have a mottled green or yellow appearance, show mosaic (e.g. chlorotic spotting) and ringspots (chlorotic or necrotic rings). [7] However, there are no signs of the viral pathogen itself, as compared to visible spores of fungal pathogens and bacterial ooze or water-soaked lesions of bacterial spots as the viruses are difficult to see and requires an electron microscope for detection. [5]

Effect on transpiration

Transpiration increases in affected plants. This is because in leaf spots, the plant cuticle, epidermis, and cell tissues, including the xylem may be destroyed in the infected areas. The cuticle protects the leaf and the destruction of these cell tissues results in an uncontrollable loss of water from the affected areas. This can result in wilting of leaves. [7]

Effect on plant growth

Leaf spots reduce the surface area available on leaves for photosynthesis and so can result in smaller growth and yield of plants. Weakened plants may produce lesser fruit. Virus caused leaf spots reduces chlorophyll in the leaves, resulting in less photosynthetic activity. This can lead to smaller leaves and blossoms, smaller growth and reduced yield. [1]

Disease cycle

Leaf spot disease occurs when the following factors are all present: favourable environmental conditions, a pathogenic agent, and susceptible host. [2] Different types of pathogens, including fungal, bacterial and viral agents have unique ways to suppress and attack the host plant's immune system, thereby resulting in the progression of leaf spot disease. Knowing the disease cycle of each microbial agent also helps in managing leaf spot disease. [2]

Fungal leaf spot pathogens follow the path of attaching to the plant surface, germinating via spores and entering into the host tissue. Colonisation of the host tissue follows and then the expression of symptoms. [14] Usually fungi will overwinter on fallen leaves, or buds, branches and fruits, then in the warmer early spring to summer months produce spores during the germination process, on the exterior of leaves, as well as exist as pycnidia, acervuli and perithecia, within the affected leaf tissue. [15]

Viruses can survive in cells that have been infected by the viral agent called alternate hosts. [2] For infection to occur virus replication needs to happen, and in doing so uses the host cell's products, disrupting cell processes. [16] Horizontal transmission of viral pathogens include dispersal through touching of nearby infected leaves and through root systems or through vectors for more distant hosts. [16] Vertical transmission occurs by inheriting the virus from the parent host plant. [16]

Bacterial pathogens survive in infected plants, plant debris, seed and soil. [8] Infection occurs when the bacteria enter into wounds, or by natural entry (cell adhesion), under favourable warm and moist conditions. [8]

Dispersion

Pathogens can be dispersed by the wind that can lift nematode eggs, insects, and many tiny fungal spores as well as bacterial cells by air currents. [2] Animal and insect vectors are another way in which fungal, bacterial and viral leaf spot diseases are spread. [2]

Rainwater spreads pathogens by transporting infested soil into areas that are disease-free. Infested water can also be spread by way of irrigation or transplanting. Blowing rain can also spread fungi and bacteria. [2] Splashing water can also spread pathogens from the soil to leaf and amongst leaves. [8]

Plant material can also be the cause of leaf spot disease. These include infected seeds, transplants and discarded culls and leaves. [2] Tools used by humans and worker's hands during transplants, watering, and market practices can contribute to the dispersal of leaf spot pathogens. [8]

Management

Certain chemicals are used to treat leaf spot disease, such as the Bordeaux mixture, the first fungicide to have been developed, which treats many fungal and bacterial leaf spots. [7] Other fungicides such as zineb, chlorothalonil and Captan, also treat leaf spot disease and Benomyl specifically treats Cercospora leaf spots, cherry leaf spot and black spot of roses. [7] Thiabendazole is used to treat leaf spot diseases of turf and ornamentals. [7] Both fenarimol and nuarimol are pyrimidines that also treats leaf spot disease. More chemicals include Triazoles an organosphosphate fungicide, Imazalil, Procholora and Fentin hydroxide. Registered fungicides in use are thiophanate methyl, chlorothalonil, ferban and mancozeb. [11]

These chemicals can be applied as foliar sprays, seed and soil treatments or as post-harvest treatment. [7]

Strains of plant pathogenic bacteria becoming resistant to chemicals contributes to the difficulty of managing bacterial leaf spot disease. An example is Xanthomanos vesicatoria, which causes bacterial spot of tomato and pepper, that is now resistant to streptomycin. Apart from chemicals, alternative management methods include using bacteriophages, bacteriocins, and heat therapy. [17]

Diversity in plant species has also been found to reduce the prevalence of leaf spot disease. The host-specific characteristic of many leaf spot pathogens makes diversity in plant species a way to reduce and regulate leaf spot pathogen infection levels within plant populations. [18]

Prevention of leaf spot disease includes variety selection, crop rotations, plant hygiene and fungicide use for seeds and foliage. [19] To stop the spread of pathogens good sanitation is key as well as the avoidance of handling plants when wet, planting pathogen-free and resistant cultivars and moving out infected plants. [20] Reducing the humidity around plants and in greenhouses by good plant spacing for air circulation, and watering early in the day can also help prevent leaf spot disease. [8] Disinfection of tools and washing of hands is important when handling infected plants. [8] Susceptibility to leaf spot disease can occur due to insufficient or excessive fertilising of plants. [8] Checking plants periodically for any signs and symptoms of disease is also good practice. [8] Avoiding overhead watering and increasing air circulation by pruning plants should be done to prevent humid conditions. [11] Collecting and removing fallen leaves is important in reducing the amount of pathogenic agents on the ground to prevent dispersal of disease. [11]

Fungicides should be used only when necessary, and if applied, early before the leaf spot disease progresses. [21] Chemical control is necessary for severe leaf spotting and defoliation occurring over several years. [21]

See also

Related Research Articles

Pyrenophora teres is a necrotrophic fungal pathogen of some plant species, the most significant of which are economically important agricultural crops such as barley. Toxins include aspergillomarasmine A and related compounds.

<span class="mw-page-title-main">Halo blight</span> Bacterial plant disease

Halo blight of bean is a bacterial disease caused by Pseudomonas syringae pv. phaseolicola. Halo blight’s pathogen is a gram-negative, aerobic, polar-flagellated and non-spore forming bacteria. This bacterial disease was first discovered in the early 1920s, and rapidly became the major disease of beans throughout the world. The disease favors the places where temperatures are moderate and plentiful inoculum is available.

Pseudopeziza medicaginis is a fungal pathogen of alfalfa.

<i>Mycosphaerella coffeicola</i> Species of fungus

Mycosphaerella coffeicola is a sexually reproducing fungal plant pathogen. It is most commonly referred to as the asexual organism Cercospora coffeicola.

<i>Zymoseptoria tritici</i> Species of fungus

Zymoseptoria tritici, synonyms Septoria tritici, Mycosphaerella graminicola, is a species of filamentous fungus, an ascomycete in the family Mycosphaerellaceae. It is a wheat plant pathogen causing septoria leaf blotch that is difficult to control due to resistance to multiple fungicides. The pathogen today causes one of the most important diseases of wheat.

<i>Corynespora cassiicola</i> Species of fungus

Corynespora cassiicola is a species of fungus well known as a plant pathogen. It is a sac fungus in the family Corynesporascaceae. It is the type species of the genus Corynespora.

<i>Ascochyta</i> Genus of fungi

Ascochyta is a genus of ascomycete fungi, containing several species that are pathogenic to plants, particularly cereal crops. The taxonomy of this genus is still incomplete. The genus was first described in 1830 by Marie-Anne Libert, who regarded the spores as minute asci and the cell contents as spherical spores. Numerous revisions to the members of the genus and its description were made for the next several years. Species that are plant pathogenic on cereals include, A. hordei, A. graminea, A. sorghi, A. tritici. Symptoms are usually elliptical spots that are initially chlorotic and later become a necrotic brown. Management includes fungicide applications and sanitation of diseased plant tissue debris.

Cercospora arachidicola is a fungal ascomycete plant pathogen that causes early leaf spot of peanut. Peanuts originated in South America and are cultivated globally in warm, temperate and tropical regions.

Alternaria dauci is a plant pathogen. The English name of the disease it incites is "carrot leaf blight".

<i>Alternaria solani</i> Species of fungus

Alternaria solani is a fungal pathogen that produces a disease in tomato and potato plants called early blight. The pathogen produces distinctive "bullseye" patterned leaf spots and can also cause stem lesions and fruit rot on tomato and tuber blight on potato. Despite the name "early," foliar symptoms usually occur on older leaves. If uncontrolled, early blight can cause significant yield reductions. Primary methods of controlling this disease include preventing long periods of wetness on leaf surfaces and applying fungicides. Early blight can also be caused by Alternaria tomatophila, which is more virulent on stems and leaves of tomato plants than Alternaria solani.

<i>Ascochyta pisi</i> Species of fungus

Ascochyta pisi is a fungal plant pathogen that causes ascochyta blight on pea, causing lesions of stems, leaves, and pods. These same symptoms can also be caused by Ascochyta pinodes, and the two fungi are not easily distinguishable.

<i>Cercospora sojina</i> Species of fungus

Cercospora sojina is a fungal plant pathogen which causes frogeye leaf spot of soybeans. Frog eye leaf spot is a major disease on soybeans in the southern U.S. and has recently started to expand into the northern U.S. where soybeans are grown. The disease is also found in other soybean production areas of the world.

<i>Cercospora melongenae</i> Fungal disease of eggplant leaves

Cercospora melongenae is a fungal plant pathogen that causes leaf spot on eggplant. It is a deuteromycete fungus that is primarily confined to eggplant species. Some other host species are Solanum aethiopicum and Solanum incanum. This plant pathogen only attacks leaves of eggplants and not the fruit. It is fairly common among the fungi that infect community gardens and home gardens of eggplant. Generally speaking, Cercospora melongenae attacks all local varieties of eggplants, but is most severe on the Philippine eggplant and less parasitic on a Siamese variety.

<span class="mw-page-title-main">Corn grey leaf spot</span> Fungal disease of maize

Grey leaf spot (GLS) is a foliar fungal disease that affects maize, also known as corn. GLS is considered one of the most significant yield-limiting diseases of corn worldwide. There are two fungal pathogens that cause GLS: Cercospora zeae-maydis and Cercospora zeina. Symptoms seen on corn include leaf lesions, discoloration (chlorosis), and foliar blight. Distinct symptoms of GLS are rectangular, brown to gray necrotic lesions that run parallel to the leaf, spanning the spaces between the secondary leaf veins. The fungus survives in the debris of topsoil and infects healthy crops via asexual spores called conidia. Environmental conditions that best suit infection and growth include moist, humid, and warm climates. Poor airflow, low sunlight, overcrowding, improper soil nutrient and irrigation management, and poor soil drainage can all contribute to the propagation of the disease. Management techniques include crop resistance, crop rotation, residue management, use of fungicides, and weed control. The purpose of disease management is to prevent the amount of secondary disease cycles as well as to protect leaf area from damage prior to grain formation. Corn grey leaf spot is an important disease of corn production in the United States, economically significant throughout the Midwest and Mid-Atlantic regions. However, it is also prevalent in Africa, Central America, China, Europe, India, Mexico, the Philippines, northern South America, and Southeast Asia. The teleomorph of Cercospora zeae-maydis is assumed to be Mycosphaerella sp.

In biology, a pathogen, in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.

<span class="mw-page-title-main">Southern corn leaf blight</span> Fungal disease of maize

Southern corn leaf blight (SCLB) is a fungal disease of maize caused by the plant pathogen Bipolaris maydis.

<i>Xanthomonas campestris</i> pv. <i>vesicatoria</i> Species of bacterium

Xanthomonas campestris pv. vesicatoria is a bacterium that causes bacterial leaf spot (BLS) on peppers and tomatoes. It is a gram-negative and rod-shaped. It causes symptoms throughout the above-ground portion of the plant including leaf spots, fruit spots and stem cankers. Since this bacterium cannot live in soil for more than a few weeks and survives as inoculum on plant debris, removal of dead plant material and chemical applications to living plants are considered effective control mechanisms.

<i>Taphrina caerulescens</i> Species of fungus

Taphrina caerulescens is a species of fungus in the family Taphrinaceae. It is a pathogenic Ascomycete fungus that causes oak leaf blister disease on various species of oak trees. The associated anamorph species is Lalaria coccinea, described in 1990. This disease causes lesions and blisters on Oak leaves. Effects of the disease are mostly cosmetic. Although not taxonomically defined, strains of T. caerulescens have been shown to be host specific with varying ¬ascus morphology between strains. There are differences in strains' abilities to metabolize various carbon and nitrogen compounds. This has been proposed as a method of taxonomically defining subspecies within T. caerulescens.

Bacterial leaf streak (BLS), also known as black chaff, is a common bacterial disease of wheat. The disease is caused by the bacterial species Xanthomonas translucens pv. undulosa. The pathogen is found globally, but is a primary problem in the US in the lower mid-south and can reduce yields by up to 40 percent.[6] BLS is primarily seed-borne and survives in and on the seed, but may also survive in crop residue in the soil in the off-season. During the growing season, the bacteria may transfer from plant to plant by contact, but it is primarily spread by rain, wind and insect contact. The bacteria thrives in moist environments, and produces a cream to yellow bacterial ooze, which, when dry, appears light colored and scale-like, resulting in a streak on the leaves. The invasion of the head of wheat causes bands of necrotic tissue on the awns, which is called Black Chaff.[14] The disease is not easily managed, as there are no pesticides on the market for treatment of the infection. There are some resistant cultivars available, but no seed treatment exists. Some integrated pest management (IPM) techniques may be used to assist with preventing infection although, none will completely prevent the disease.[2]

<span class="mw-page-title-main">Alternaria leaf spot</span> Fungal plant disease

Alternaria leaf spot or Alternaria leaf blight are a group of fungal diseases in plants, that have a variety of hosts. The diseases infects common garden plants, such as cabbage, and are caused by several closely related species of fungi. Some of these fungal species target specific plants, while others have been known to target plant families. One commercially relevant plant genus that can be affected by Alternaria Leaf Spot is Brassica, as the cosmetic issues caused by symptomatic lesions can lead to rejection of crops by distributors and buyers. When certain crops such as cauliflower and broccoli are infected, the heads deteriorate and there is a complete loss of marketability. Secondary soft-rotting organisms can infect stored cabbage that has been affected by Alternaria Leaf Spot by entering through symptomatic lesions. Alternaria Leaf Spot diseases that affect Brassica species are caused by the pathogens Alternaria brassicae and Alternaria brassicicola.

References

  1. 1 2 3 4 Horst, R. (2008). Westcott’s Plant Disease Handbook  (Seventh Edition.). Springer Netherlands.
  2. 1 2 3 4 5 6 7 8 Lucas, G., & Campbell, L. (1992). Introduction to Plant Diseases Identification and Management  (2nd ed. 1992.). Springer US. https://doi.org/10.1007/978-1-4615-7294-7
  3. 1 2 Gunsolus, J. L. (1999). Herbicide Mode of Action and Injury Symptoms. North Central Regional Extension Publications, 377, 1–24. Retrieved from https://appliedweeds.cfans.umn.edu/sites/appliedweeds.cfans.umn.edu/files/herbicide_mode_of_action_and_injury_symptoms.pdf
  4. 1 2 Grabowsk, M. & University of Minnesota Extension. (2018). Leaf spot diseases of trees and shrubs. Retrieved 9 September 2020, from https://extension.umn.edu/plant-diseases/leaf-spot-diseases-trees-and-shrubs#leaf-rusts-1156511
  5. 1 2 Isleib, J. & Michigan State University Extension. (2012). Signs and symptoms of plant disease: Is it fungal, viral or bacterial? Retrieved 10 October 2020, from https://www.canr.msu.edu/news/signs_and_symptoms_of_plant_disease_is_it_fungal_viral_or_bacterial
  6. 1 2 University of Maryland Extension. (2020). Foliar Nematodes - Flowers | University of Maryland Extension. Retrieved 10 October 2020, from https://extension.umd.edu/hgic/topics/foliar-nematodes-flowers
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Agrios, G. N. (2005). Plant Pathology (5th ed.). https://doi.org/10.1016/C2009-0-02037-6
  8. 1 2 3 4 5 6 7 8 9 10 Dicklow, M. B. (2019, October 8). Leaf Spot Diseases of Floricultural Crops Caused by Fungi and Bacteria. Retrieved from https://ag.umass.edu/greenhouse-floriculture/fact-sheets/leaf-spot-diseases-of-floricultural-crops-caused-by-fungi
  9. 1 2 Cotton Incorporated. (2020, January 24). Plant Pathology - Diagnosis and Management of Foliar Diseases. Retrieved from https://www.cottoninc.com/cotton-production/ag-research/plant-pathology/diagnosis-management-foliar-diseases-2/
  10. Agriculture Victoria. (2020, November 24). Yellow leaf spot of wheat - Agriculture. Retrieved 7 December 2020, from https://agriculture.vic.gov.au/biosecurity/plant-diseases/grain-pulses-and-cereal-diseases/yellow-leaf-spot-of-whea
  11. 1 2 3 4 Douglas, S. M. (2020). Fungal Leaf Spots of Trees and Ornamentals. Retrieved from https://portal.ct.gov/CAES/Fact-Sheets/Plant-Pathology/Fungal-Leaf-Spots-of-Trees-and-Ornamentals
  12. 1 2 Koike, S. T., Turini, T. A., & Davis, R. M. (2017). Bacterial Leaf Spot / Lettuce / Agriculture: Pest Management Guidelines / UC Statewide IPM Program (UC IPM). Retrieved 10 October 2020, from https://www2.ipm.ucanr.edu/agriculture/lettuce/Bacterial-leaf-spot/
  13. University of Illinois Extension. (2020). Bacterial Leaf Spot (Pseudomonas spp. & Xanthomonas spp.)-Hort Answers - University of Illinois Extension. Retrieved 10 October 2020, from https://web.extension.illinois.edu/hortanswers/detailproblem.cfm?PathogenID=152
  14. Narayanasamy, P. (2008). Molecular Biology in Plant Pathogenesis and Disease Management : Disease Development Volume 2. Springer Netherlands.
  15. Pataky, N. R. (1998). Fungal leaf spot diseases of shade and ornamental trees in the midwest. University of Illinois Extension, 648, 1–8. Retrieved from https://ipm.illinois.edu/diseases/rpds/648.pdf
  16. 1 2 3 Burchett, S., & Burchett, S. (2017). Plant pathology. Garland Science, Taylor & Francis Group. doi : 10.1201/9781315144924
  17. Thind, B. S. (2015). Diagnosis and Management of Bacterial Plant Diseases. In L. P. Awasthi (Ed.), Recent Advances in the Diagnosis and Management of Plant Diseases (pp. 101–117). doi : 10.1007/978-81-322-2571-3_10
  18. Rottstock, T. (2014). Higher plant diversity promotes higher diversity of fungal pathogens, while it decreases pathogen infection per plant. Ecology, 95(7), 1907–1917. doi : 10.1890/13-2317.1
  19. Grains Research & Development Corporation. (2018, July). Grownotes, Lupin, Section 8, Foliar Diseases (8). GRDC. Retrieved from https://grdc.com.au/__data/assets/pdf_file/0022/366115/GrowNote-Lupin-West-8-Foliar-Diseases.pdf
  20. Agriculture Victoria. (2020a, November 24). Bacterial leaf spot of ornamentals and vegetables - Agriculture. Retrieved from https://agriculture.vic.gov.au/biosecurity/plant-diseases/vegetable-diseases/bacterial-leaf-spot-of-ornamentals-and-vegetables
  21. 1 2 Nix, S. (2017, November 29). How to Prevent and Control Leaf Spot Tree Disease. Retrieved from https://www.thoughtco.com/leaf-spot-tree-disease-prevention-control-1342869