Cherry leaf spot (''Blumeriella jaapii'') is a fungal disease which infects

cherries A cherry is the fruit of many plants of the genus ''Prunus'', and is a fleshy drupe (stone fruit). Commercial cherries are obtained from cultivars of several species, such as the sweet ''Prunus avium'' and the sour ''Prunus cerasus''. The name ...

and

plum A plum is a fruit of some species in Prunus subg. Prunus, ''Prunus'' subg. ''Prunus'.'' Dried plums are often called prunes, though in the United States they may be labeled as 'dried plums', especially during the 21st century. Plums are ...

Sweet Sweetness is a basic taste most commonly perceived when eating foods rich in sugars. Sweet tastes are generally regarded as pleasurable. In addition to sugars like sucrose, many other chemical compounds are sweet, including aldehydes, ketones, ...

sour The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth biochemistry, reacts chemically with taste receptor cells l ...

, and ornamental cherries are susceptible to the disease, being most prevalent in sour cherries. The variety of sour cherries that is the most susceptible are the English morello cherries. This is considered a serious disease in the

Midwest The Midwestern United States (also referred to as the Midwest, the Heartland or the American Midwest) is one of the four census regions defined by the United States Census Bureau. It occupies the northern central part of the United States. It ...

New England New England is a region consisting of six states in the Northeastern United States: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. It is bordered by the state of New York (state), New York to the west and by the ...

states, and

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. It has also been estimated to infect 80 percent of orchards in the Eastern states.Gianessi, L., Williams, & Ashley. (2011, May). Crop Life Foundation. Retrieved from Fungicides Prevent Defoliation of Cherry Trees in Eastern States: http://croplifefoundation.files.wordpress.com/2012/07/14-cherries.pdf It must be controlled yearly to avoid a significant loss of the crop. If not controlled properly, the disease can dramatically reduce yields by nearly 100 percent. The disease is also known as yellow leaf or shothole disease to cherry growers due to the characteristic yellowing leaves and shot holes present in the leaves upon severe infection.Farmer, B. (n.d.). UNL Extension: Controlling Cherry Leaf Spot. Retrieved from University of Nebraska-Lincoln:

Host and symptoms

Cherry leaf spot is caused by the

ascomycete Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The def ...

fungus ''Blumeriella jaapii'' (formerly known as ''Coccomyces hiemalis'';

anamorph In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota: *Teleomorph: the sexual reproductive stage (morph), typically a fruiting body. *Anamorph: an ase ...

''Phloeosporella padi''). This fungus overwinters in dead leaves on the ground as its main form of survival. In the spring,

apothecia An ascocarp, or ascoma (: ascomata), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. As ...

develop on these leaves.

Ascospore In fungi, an ascospore is the sexual spore formed inside an ascus—the sac-like cell that defines the division Ascomycota, the largest and most diverse Division (botany), division of fungi. After two parental cell nucleus, nuclei fuse, the ascu ...

s are produced in these fungal fruiting bodies and are forcibly ejected during rainy periods for about 6–8 weeks, starting at petal fall. This is the

teleomorph In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota: *Teleomorph: the sexual reproductive stage (morph), typically a fruiting body. *Anamorph: an ase ...

or sexual stage and results in new genetic recombination and variation for the disease.Agrios, G. N. (1997). Plant Pathology (4 ed.). San Diego, California, US: Academic Press. This

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), 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 theory of d ...

mainly affects and is most noticeable on the leaves of cherry trees. The most obvious symptom of this disease is the yellowing of leaves before they drop in the early spring. Infected leaves are filled with numerous black lesions that cover an obvious portion of the leaf.Ellis, M. A. (2008). Cherry Leaf Spot. Columbus, OH: The Ohio State University, Department of Plant Pathology. Retrieved from http://ohioline.osu.edu/hyg-fact/3000/pdf/HYG_3021_08.pdf These lesions first appear as small purple spots which turn red to brown and then black. Most spots are circular but can amalgamate to form large, irregular dead patches. These spots tend to enlarge and separate from healthy tissue. Lastly, they drop out of the leaf giving a "shot-hole" appearance. This shot hole effect is more common on sour than on sweet cherries. In more severe and advanced cases, lesions are found on the fruit, petioles, and stems. Leaves with lesions present typically fall off early in the growing season and it is common for seriously affected trees to be defoliated by

midsummer Midsummer is a celebration of the season of summer, taking place on or near the date of the summer solstice in the Northern Hemisphere; the longest Daytime, day of the year. The name "midsummer" mainly refers to summer solstice festivals of Eu ...

. Leaves severely infected by the disease turn very yellow before falling off. If the disease is not controlled and allowed to persist for several years there could be various adverse effects to the overall cherry production of a tree primarily due to the cycle of early season and repeated

defoliation A defoliant is any Herbicide, herbicidal chemical sprayed or dusted on plants to cause their Leaf, leaves to fall off. Defoliants are widely used for the selective removal of weeds in managing croplands and lawns. Worldwide use of defoliants, ...

. These effects include dwarfed and unevenly ripened fruit which has poor taste, trees more susceptible to winter injury, death of fruit spurs, small and weak fruit buds, decreased fruit size and set, and eventual death of the tree. If the disease has significantly infected the leaves enough in early spring it is possible that the fruit will fail to mature in that year. This fruit will typically remain light colored, soft, and very low in soluble solids and sugar.

Disease cycle

Sexual reproduction

This fungus overwinters in dead leaves on the ground. In early spring (at the time of petal fall), fungal fruiting bodies called

develop in these leaves.

s produced in the apothecia are forcibly discharged into the air starting at petal fall. They can start new infections in new, green leaves and serve as the primary inoculum in each new growing season. The ascospores can stick to the leaf and, given a film of water and optimal temperature, germinate within hours of adhesion. Upon

germination Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, ...

, hyphae can grow into the leaf via

stoma In botany, a stoma (: stomata, from Greek language, Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the Epidermis (botany), epidermis of leaves, stems, and other organs, that controls the rate of gas exc ...

ta (natural openings) on the underside of the leaf.Cherry Leaf Spot. (2013). Retrieved from Penn State Extension: http://extension.psu.edu/plants/gardening/fphg/stone/diseases/cherry-leaf-spot Hyphae cannot invade immature stomata very effectively.Travis, J., Rytter, J., & Biggs, A. (n.d.). Cherry Leaf Spot. Kearneysville, WV: West Virginia University, Fruit Pathology. Retrieved from http://www.caf.wvu.edu/kearneysville/disease_descriptions/omchlfsp.html After invasion, the hyphae grow in the intercellular spaces in the leaf, killing and feeding on leaf tissues. Incubation times vary with available moisture and temperature. The small purple lesions can appear within 5 days if there are damp conditions and the temperature remains steady between , or up to 15 days in lower temperatures and drier conditions. Leaves become less susceptible to infection as they age. The first sign of disease may be on the suckers close to the ground. Sexual reproduction is associated with the primary infection cycle of cherry leaf spot. Infection levels in this primary cycle are low, but essential for the success of the pathogen. Because the ascospores are produced through sexual reproduction, this part of the life cycle can also introduce genetic variation that may be important, for example, in the evolution of fungicide resistance. Conidia of cherry leaf spot

Asexual reproduction

Once these lesions from the primary infection have formed, there is the potential for

secondary infection infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...

s. Secondary or summer spores called

conidia A conidium ( ; : conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (: chlamydoconidia), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also ...

form in whitish patches on the undersides of leaves in tiny, concave fruiting bodies called acervuli. These conidia are horn-shaped and have hydrophilic outer cell walls that make them easily miscible in water. When spread during rain or by wind they can cause new leaf infections. Each conidium can multiply to form many additional conidia relatively quickly. When conditions are favorable, additional infections caused by conidia may overwhelm plant defenses, leading the plant to shed badly infected leaves. These secondary infections allow the disease to escalate into an

epidemic An epidemic (from Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of hosts in a given population within a short period of time. For example, in meningococcal infection ...

very quickly. The conidia form through an asexual process, so all the conidia formed in one leaf spot are genetically identical. The fungus overwinters in diseased leaves on the ground, producing sexual spores in the Spring that infect the emerging leaves.

Environment

The disease is generally distributed throughout the

U.S. The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 states and a federal capital district, Washington, D.C. The 48 contiguous ...

, Canada, and various parts of the world where humid conditions occur. The cherry leaf spot fungus prefers moderately wet conditions, with temperatures above . Optimal temperature range for the spread of this fungus is between .Sundin, G. (2013, June 7). Fungicide considerations for cherry leaf spot control at first cover. Retrieved December 3, 2013, from Michigan State University Extension: http://msue.anr.msu.edu/news/fungicide_considerations_for_cherry_leaf_spot_control_at_first_cover Serious infection of a tree occurs in years with many rainy periods and cooler summers. Very few ascospores are ejected from the apothecia if the temperature is less than . This disease thrives in areas that do not use any type of sanitation practice as a preventative measure to prevent disease spread. When selecting a site for an orchard, use areas that have well drained soils, much sunlight, and good air circulation.

Disease management

Resistance

There are no resistant varieties available on the commercial market yet. However, researchers have found the a

wild type The wild type (WT) is the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard "normal" allele at a locus, in contrast to that produced by a non-standard, " ...

gene linked to the resistance. They are currently

crossbreeding A crossbreed is an organism with purebred parents of two different breeds, varieties, or populations. A domestic animal of unknown ancestry, where the breed status of only one parent or grandparent is known, may also be called a crossbreed though ...

the wild lines with commercial

cultivar A cultivar is a kind of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and which retains those traits when Plant propagation, propagated. Methods used to propagate cultivars include division, root a ...

s and beginning to carry out field trials. No data is available yet.

Small or backyard growers

For small or backyard growers, collecting and destroying all leaf debris on the ground is an absolute necessity due to the potency of this disease because the fungus overwinters in this leftover leaf litter. This is its main form of survival. By removing and destroying these leaves, a grower can significantly decrease the amount of primary inoculum available in the spring. It will greatly decrease the apparent infection rate. There has also been a study done on the addition of a

straw Straw is an agricultural byproduct consisting of the dry wikt:stalk, stalks of cereal plants after the grain and chaff have been removed. It makes up about half of the crop yield, yield by weight of cereal crops such as barley, oats, rice, ry ...

mulch A mulch is a layer of material applied to the surface of soil. Reasons for applying mulch include conservation of soil moisture, improving soil fertility, fertility and health of the soil, reducing Weed control, weed growth, and enhancing the v ...

bedding to the ground after all the leaves have been picked up. The addition of this mulch further reduced the spring infection rate.

Leaf litter Plant litter (also leaf litter, tree litter, soil litter, litterfall, or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that has fallen to the ground. This detritus or dead organic material and its constituen ...

removal is not very practical for large commercial growers due labor needs and number of trees but if at all possible, a majority of the old leaves should try to be collected. When planting, growers should select locations which have a large amount of direct sunlight such as a south facing slope. Proper pruning should also be completed to increase the amount of sunlight penetration and air circulation through the

canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapes Religion and ceremonies * Baldachin or canopy of state, typically placed over an a ...

. Any practice that increases the faster drying of leaves will help reduce the risk of infection. Growers may also consider making an after harvest

fungicide Fungicides are pesticides used to kill parasitic fungi or their spores. Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals, ...

application using a combination of

Benomyl Benomyl (also marketed as Benlate) is a fungicide introduced in 1968 by DuPont. It is a systemic benzimidazole fungicide that is selectively toxic to microorganisms and invertebrates (especially earthworms), but relatively nontoxic toward mammals. ...

(50% WP) and

Captan Captan is a general use pesticide (GUP) that belongs to the phthalimide class of fungicides. It is a white solid, although commercial samples appear yellow or brownish. Applications Although it can be applied on its own, Captan is often added as ...

(50% WP) at rates of ¼

Tablespoon A tablespoon (tbsp., Tbsp., Tb., or T.) is a large spoon. In many English-speaking regions, the term now refers to a large spoon used for serving; however, in some regions, it is the largest type of spoon used for eating. By extension, the ter ...

and 2 Tablespoons respectively per

gallon The gallon is a unit of volume in British imperial units and United States customary units. The imperial gallon (imp gal) is defined as , and is or was used in the United Kingdom and its former colonies, including Ireland, Canada, Australia ...

of water. This will help reduce the rate at which pathogens may develop resistance to Benomyl products. Prior to

shuck split Shuck may refer to: *The chaff sections of grains *Black Shuck, mythical dog *Shuckin' and jivin' *"Shuck", a song by Purity Ring from their debut album, ''Shrines (Purity Ring album), Shrines'' (2012) People *Glenn Shuck, American academic *Henr ...

, the recommended fungicide for cherry leaf spot is

chlorothalonil Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile) is an organic compound mainly used as a broad spectrum, nonsystemic fungicide, with other uses as a wood protectant, pesticide, acaricide, and to control Mold (fungus), mold, mildew, bacteria ...

(Bravo and generics). This fungicide is a multi-site protectant and is excellent for leaf spot control and is not at risk for fungicide resistance development. At least two applications of chlorothalonil should be made before shuck split with the goal to minimize the potential of infection at this early stage.

Commercial growers

For commercial growers, the disease is primarily controlled by use of fungicide sprays. Fungicides are much more effective when applied early in the season when the inoculum load is low as cherry leaf spot is a prolific, unrelenting, tireless disease. Fungicide applications should begin at petal fall or shortly after leaves have unfolded. These sprays should continue on a schedule of every 7–10 days until harvest. Upon harvest, one or two postharvest applications should be administered, beginning 2–3 weeks after harvest. It is suggested that spraying alternate sides of trees on a 7-day program is more effective than spraying both sides of trees on a 10-day schedule.

Michigan State University Michigan State University (Michigan State or MSU) is a public university, public Land-grant university, land-grant research university in East Lansing, Michigan, United States. It was founded in 1855 as the Agricultural College of the State o ...

suggests getting an early start on protection before the fungus starts infecting for the production year. This means that growers should spray at the

bract In botany, a bract is a modified or specialized leaf, associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves in size, color, shape or texture. They also lo ...

leaf stage with chlorothalonil (Bravo and generics). These bract leaves open prior to bloom, which means bract leaves could be infected early, before petal fall. Typically the first fungicide application is recommended around petal fall, but due to the early and epidemic levels of infection in found in 2012, the first application should be applied earlier. Significant infection was also found in the bract leaves in mid- to late June 2012. This was particularly surprising because the weather conditions were not notably conductive to the super development of cherry leaf spot infection. These early and significantly strong infection rates indicate that the fungus is evolving and becoming resistant to certain fungicide treatments. Control programs will need to be altered to keep up with the genetic advancement of the fungus. These earlier infections are a concern because once infection occurs; more spores will be produced from the lesions (conidia) than the leaf debris (ascospores) on the ground. These conidia are much more potent than ascospores in terms of infection rate. In addition, spores from the lesions are much closer to new uninfected leaves than the spores from the leaf debris on the ground. Due to the smaller distance, infection will occur much quicker. George Sundin, a professor and fruit extension specialist from Michigan State University advocates that the new chemistries of succinate dehydrogenase inhibitors (SDHIs) are also effective in controlling cherry leaf spot. "Pristine" was registered in 2004. It is a premix of

boscalid Boscalid is a broad spectrum fungicide used in agriculture to protect crops from fungal diseases. It was first marketed by BASF in 2002 using their brand name Endura. The compound is an biphenyl amide derived inhibitor of succinate dehydrogenase. ...

(SDHI) and

pyraclostrobin Pyraclostrobin is a quinone outside inhibitor ( QI)-type fungicide used in agriculture. Among the QIs, it lies within the strobilurin chemical class. Use Pyraclostrobin is used to protect ''Fragaria'', ''Rubus idaeus'', ''Vaccinium corymbosum'' ...

(

strobilurin Strobilurins are a group of natural products and their synthetic analogs. A number of strobilurins are used in agriculture as fungicides. They are part of the larger group of QIs (Quinone outside Inhibitors), which act to inhibit the respiratory ch ...

). This has been indicated effective at a rate of 10.5 oz/acre. Other SDHIs that may be effective in cherry leaf spot control include fluopyram (a pyramide manufactured by

Bayer Bayer AG (English: , commonly pronounced ; ) is a German multinational pharmaceutical and biotechnology company and is one of the largest pharmaceutical companies and biomedical companies in the world. Headquartered in Leverkusen, Bayer' ...

under the name "Luna") and fluxapyroxad (a

pyrazole Pyrazole is an organic compound with the chemical formula, formula . It is a heterocycle characterized as an azole with a 5-membered ring of three carbon atoms and two adjacent nitrogen atoms, which are in Arene substitution pattern, ortho-substi ...

carboxamide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent any group, typically organyl groups or hydrogen atoms. The amide group is called a pe ...

manufactured by

BASF BASF SE (), an initialism of its original name , is a European Multinational corporation, multinational company and the List of largest chemical producers, largest chemical producer in the world. Its headquarters are located in Ludwigshafen, Ge ...

under the name Merivon). Sterol demethylation inhibitor (DMI) fungicides including fenarimol, fenbuconazole,

myclobutanil Myclobutanil is a triazole chemical used as a fungicide. It is a steroid demethylation ( CYP51) inhibitor, specifically inhibiting ergosterol biosynthesis. Ergosterol is a critical component of fungal cell membranes. Stereoisomerism Safety ...

, and

tebuconazole Tebuconazole is a triazole fungicide used agriculturally to treat plant pathogenic fungi. Environmental hazards Though the U.S. Food and Drug Administration considers this fungicide to be safe for humans, it may still pose a risk. It is listed as ...

were used immensely in the 1980s and 1990s. The efficacy of DMI fungicides has decreased dramatically in recent years and have not been used greatly since 2002. In an effort to keep a high level of diversity in the cherry fungicide programs and reduce the amount of resistance building up to the DMI fungicides,

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

based fungicides can be used with great efficacy to battle the fungus. However, the copper application is associated with noticeable leaf bronzing. There has been great concern that this bronzing causes a highly negative effect on the

photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...

integrity of the leaves which in turn decreases the number of fruits per shoot, fresh fruit weight, and soluble solids concentration of the mature fruit. It has been scientifically proven that the standard application of copper based fungicides does not have any adverse effects on the developing fruit.

Importance

Cherry leaf spot has been present in the United States and

mainland Europe Continental Europe or mainland Europe is the contiguous mainland of Europe, excluding its surrounding islands. It can also be referred to ambiguously as the European continent, – which can conversely mean the whole of Europe – and, by so ...

since the 19th century. It has only become common and a problem in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

since the 1990s. The severity of the disease is very variable from year to year. In 1945 there was a serious outbreak in southern

Pennsylvania Pennsylvania, officially the Commonwealth of Pennsylvania, is a U.S. state, state spanning the Mid-Atlantic (United States), Mid-Atlantic, Northeastern United States, Northeastern, Appalachian, and Great Lakes region, Great Lakes regions o ...

. Trees began to defoliate early in the spring and eventually 25,000 trees died by the end of the growing season. This was 10 percent of Pennsylvania's cherry tree acreage at the time.Lewis, F.H. and A.B. Groves. 1948. Cherry Leaf Spot Control in the Cumberland – Shenandoah Valley. Virginia Agricultural Experiment Station Some trees were sprayed in 1945 at the end of the growing season and some trees were not. All of the trees that were sprayed in the fall of 1945 survived and produced fruit in 1946. Yields for the unsprayed trees that survived were 36 pounds per tree. Sprayed trees yielded nearly three times more than the controls with 107 pounds per tree. Additional research conducted in the 1940s demonstrated that it was absolutely necessary to monitor and control leaf spot through preventative sprays and measures. These experiments showed that poor control of the pathogen resulted in a 72 percent loss of tree branches for the growers who did not spray. Growers who used fungicides regularly and persistently commonly suffered no or very little loss from cherry leaf spot each year. More recent research studies have continued to support these findings. Work done by A. L. Jones in the 1980s and 1990s further quantified that

applications reduced defoliation from 80% to 0.3% and from 98% to 3%. Typical individual tree yields in 1992 in Michigan were approximately 80 pounds per tree, showing that spraying for the pathogen is definitely a worthwhile endeavor.Me-Nsope, Nathalie Monge. Tart Cherry Yield and Economic Response to Alternative Planting Densities. nline2009. ited: December 3, 2013.http://www.ageconsearch.umn.edu/bitstream/54502/2/2009Me-NsopeThesisc.pdf The year 2012 was problematic for Michigan growers as the early warm weather and untimely rains caused the infection to take off much earlier compared to most years.Sundin, G., & Rothwell, N. (2013, May 14).
Cherry leaf spot: get an early start on protection before the fungus gets started on infection
. Retrieved from Michigan State University Extension News.

References

{{Taxonbar, from=Q10431598 Fungal tree pathogens and diseases Stone fruit tree diseases Leaf diseases Drepanopezizaceae