![Guignardia bidwellii 08](https://upload.wikimedia.org/wikipedia/commons/c/cb/Guignardia_bidwellii_08.jpg)
Grape black rot is a
fungal disease
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from t ...
caused by an
ascomycetous
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 de ...
fungus
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...
, ''Guignardia bidwellii'', that attacks
grape
A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters.
The cultivation of grapes began perhaps 8,000 years ago, ...
vines during hot and humid weather. “Grape black rot originated in eastern
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
, but now occurs in portions of
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
,
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
, and
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
. It can cause complete crop loss in warm, humid climates, but is virtually unknown in regions with arid summers.”
The name comes from the black fringe that borders growing brown patches on the leaves. The disease also attacks other parts of the plant, “all green parts of the vine: the shoots, leaf and fruit stems, tendrils, and fruit. The most damaging effect is to the
fruit
In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering.
Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
”.
Grape black rot affects many grape growers throughout the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
, therefore, it is important to understand the disease life cycle and environmental conditions to best manage the disease. Once infection takes place, different methods are available to control the disease.
Disease cycle
The disease cycle begins with the overwintering structures. The grape black rot
pathogen
In biology, a pathogen ( el, πάθος, "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 ...
overwinters
Overwintering is the process by which some organisms pass through or wait out the winter season, or pass through that period of the year when "winter" conditions (cold or sub-zero temperatures, ice, snow, limited food supplies) make normal activi ...
in many parts of the grape vine, especially mummies and lesions, and is able to overwinter on the vineyard floor.
In fact, "Viable lesions capable of producing conidia can persist in wood for at least 2 years."
Spring rains release the ascospores and conidia contained in the overwintering structures and these spores are “spread by wind and rain‐splash to infect leaves, blossoms and young fruit”.
Some of the mummies on the ground can have a significant discharge of ascospores that begins about two to three weeks after bud breaks and will mature one to two weeks after the start of bloom.
In the presence of moisture, these
ascospores
An ascus (; ) is the sexual spore-bearing cell produced in ascomycete fungi. Each ascus usually contains eight ascospores (or octad), produced by meiosis followed, in most species, by a mitotic cell division. However, asci in some genera or ...
germinate
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, fer ...
slowly, taking 36 to 48 hours, but eventually penetrate the young leaves and fruit stems (pedicels). The infections become visible after 8 to 25 days. The period that overwintering spores require to cause infection depends on the inoculum source. If there is a large source of inoculum, the infection will set in earlier. The second type of spore,
conidia
A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to the ...
, “are dispersed short distances (inches to feet) by splashing rain drops" in rain storms throughout the summer.
Infection occurs when either of the two spore types lands on green grape tissue and the tissue remains wet for a "sufficient length of time, which is dependent on temperature."
For example, at 45°F no infection will occur regardless of moisture, while at 50°F it takes 24 hours of leaf wetness for a spore to germinate and infect the green grape tissue.
When a leaf or berry becomes infected, pycnidia form and produce conidia, contributing to repeated cycles of infections in summer rains.
At the end of the season, the fungus overwinters as pycnidia or pseudothecia within cane lesions or mummified fruit.
In the spring, the pycnidia will produce conidia once again and the pseudothecia produce ascospores.
Environmental conditions for infection
When the weather is moist, ascospores are produced and released throughout the entire spring and summer, providing continuous primary infection. The black rot fungus requires warm weather for optimal growth; cool weather slows its growth. A period of two to three days of rain, drizzle, or fog is also required for infection.
"Conidia spores can also form, within cane lesions or on mummies that have remained within the trellis, and these are dispersed by splashing rain drops.”
Raindrops transfer these spores by moving the spores to different plant parts, especially susceptible young leaves. “If water is present, the conidia germinate in 10 to 15 hours and penetrate young tissue. New black rot infections continue into late spring and summer during prolonged periods of warm, rainy weather. The conidia are capable of
germinating
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, fern ...
and causing infection several months after being formed. During August, the
pycnidia
A pycnidium (plural pycnidia) is an asexual fruiting body produced by mitosporic fungi, for instance in the order Sphaeropsidales ( Deuteromycota, Coelomycetes) or order Pleosporales (Ascomycota, Dothideomycetes). It is often spherical or inve ...
are transformed into an overwintering stage that, in turn, gives rise to
pseudothecia
An ascocarp, or ascoma (), 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. Ascocarps are mo ...
within which the spring spores (ascospores) are produced. This ascospore is "forcibly discharged into the air and can travel considerable distances."
"Research has shown that ascospores are an important source of primary infections in the spring."
In the spring during wet weather, the "
pycnidia
A pycnidium (plural pycnidia) is an asexual fruiting body produced by mitosporic fungi, for instance in the order Sphaeropsidales ( Deuteromycota, Coelomycetes) or order Pleosporales (Ascomycota, Dothideomycetes). It is often spherical or inve ...
on infected tissues absorb water and conidia are squeezed out."
"Conidia are splashed about randomly by rain and can infect any young tissue in less than 12 hours at temperatures between 60-90 degrees."
A film of water on the vine surface is necessary for the infection to
inoculate
Inoculation is the act of implanting a pathogen or other microorganism. It may refer to methods of artificially inducing immunity against various infectious diseases, or it may be used to describe the spreading of disease, as in "self-inoculati ...
.
This completes the disease cycle.
Symptoms
Relatively small, brown circular
lesion
A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals.
Types
There is no designated classifi ...
s develop on infected leaves and within a few days tiny black spherical fruiting bodies (
pycnidia
A pycnidium (plural pycnidia) is an asexual fruiting body produced by mitosporic fungi, for instance in the order Sphaeropsidales ( Deuteromycota, Coelomycetes) or order Pleosporales (Ascomycota, Dothideomycetes). It is often spherical or inve ...
) protrude from them. Elongated black lesions on the
petiole may eventually girdle these organs, causing the affected leaves to wilt. Shoot infection results in large black elliptical lesions. These lesions may contribute to breakage of shoots by wind, or in severe cases, may girdle and kill young shoots altogether. This fungus bides its time. Most plants show very little signs of infection until its too late. They will look very healthy until fruit sets. Even flowering will be normal.
Infection of the fruit is the most serious phase of the disease and may result in substantial economic loss. Infected berries first appear light or chocolate brown; it will have a spot that looks very round, like the eye of a bird. That spot will get larger and infect more of the fruit bunch and more of the plant. This creates masses of black pycnidia developing on the surface. Finally, infected berries shrivel and turn into hard black
raisin
A raisin is a dried grape. Raisins are produced in many regions of the world and may be eaten raw or used in cooking, baking, and brewing. In the United Kingdom, Ireland, New Zealand, and Australia, the word ''raisin'' is reserved for the d ...
-like bodies that are called mummies.
Control and management
A mixture of cultural and chemical control practices can manage grape black rot disease caused by ''Guignardia bidwellii''. Cultural control aspects involve the basics in plant care and field sanitation as well as cleanup after an infectious outbreak. Chemical control has a large influence to prevent but not eliminate disease.
Cultural control
Cultural control consists of the management of the fields and sanitation methods to optimally grow grape crops.
Many universities and professors suggest the following cultural control practices:
The first cultural control method is to choose the right grape cultivar for the region that the grape will be grown in. Grape cultivars differ in their susceptibility to diseases, including differences in the disease black rot. Some varieties are less susceptible, while others are more prone to the disease when the right environmental conditions occur. Through research, many lists of grapes varieties will show the amount of resistance a variety has to disease and how the variety should be grown. A
list of grape varieties
This list of grape varieties includes cultivated grapes, whether used for wine, or eating as a table grape, fresh or dried (raisin, currant, sultana). For a complete list of all grape species including those unimportant to agriculture, see Viti ...
is a good place to start for selecting the right grape variety.
Proper grape management in the field is important to control black rot disease. The placement of the grape plants is important to provide for proper
aeration
Aeration (also called aerification or aeriation) is the Systems engineering process, process by which air is circulated through, mixed with or solvation, dissolved in a liquid or other substances that act as a fluid (such as soil). Aeration proces ...
and lighting. “Choose a planting site where the vines will be exposed to full sun and good air circulation.”
Proper training of grape vines should be practiced. Many people use
trellising to keep the vines off the ground. Trellising is a form of plant training, which is the arrangement of plant parts spatially to optimize productivity. Having the grape vines off the ground “reduces the time that vines remain wet from
dew
Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening due to condensation.
As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that at wh ...
and rain and thus limits the amount of infection”.
As the current seasons growth occurs, tie the new growth in a spatial manner to allow for air circulation and sunlight to affect the whole grape plant.
A proper
pruning
Pruning is a horticultural, arboricultural, and silvicultural practice involving the selective removal of certain parts of a plant, such as branches, buds, or roots.
The practice entails the ''targeted'' removal of diseased, damaged, dead, ...
technique is another cultural control method to limit diseases. Prune each vine every year during the dormant period. This dormant pruning is heavily researched to provide the term-balanced pruning. This is done by using the weight of the previous year’s cane growth (1- yr-old canes) to determine how many buds should be retained for the current production year. Up to four pounds of pruning can occur during the season. Remove excess growth, diseased and overwintering berries, leaves, and tendrils from the vineyard, and burn or otherwise destroy them.
This practice reduces
inoculum
In biology, inoculum refers to the source material used for inoculation. ''Inoculum'' may refer to:
* In medicine, material that is the source of the inoculation in a vaccine
* In microbiology, propagules: cells, tissue, or viruses that are used t ...
of the fungus, thus limiting disease. During the season, minor pruning to train 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 ...
growth may occur to help with aeration.
The last cultural control method would be to maintain clean fields once infected. Keep the field well managed, do not allow overgrowth of weeds or plants near the grapes. Once the plants have been infected “Remove all mummies from the canopy during the dormant pruning process. Mummies produce spores next to the susceptible grapevine tissues throughout the season; even relatively few can cause significant damage.”
Another technique to rid of infection can be to “cultivate the vineyard before bud-break to bury the mummified berries. Diseased berries covered with soil do not produce spores that will reach the developing vines”.
Chemical control
The use of
chemical control is widely available for agricultural purposes. To apply chemical applications, look at the
fungicide
Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality, ...
label for proper use. Be sure that the conditions are optimal to spray to avoid drift and inefficiencies of the fungicide due to application. Fungicide guidelines must be followed. There are a wide variety of chemicals that are available for both regular and organic growers.
Commercially, application of fungicides may be costly. To cut down on costs, one must understand the life cycle of the pathogens. Different fungicides are more effective at certain infection stages. Understand that throughout the development of the plant, different fungicides should be considered to protect plant health. In order to cut down on spraying costs, it is important to understand life cycle of the pathogen. “Research in
New York
New York most commonly refers to:
* New York City, the most populous city in the United States, located in the state of New York
* New York (state), a state in the northeastern United States
New York may also refer to:
Film and television
* '' ...
demonstrated berries of most varieties become resistant to black rot infection 3-4 weeks after bloom, therefore, sprays for black rot should not be needed at this time”.
Understanding times to limit application is important for good production practices. This shows that preventative chemical measures before the three to four weeks would be optimal. Each region should develop their own fungicide application program in correlation with cultural practices.
The most common fungicides that prove to be excellent for certain regions of the United States for controlling black rot are Sovran 50WG, Flint 50WG, Abound Flowable (2.08F), and Pristine 38WDG. Some of these fungicides may only be available for commercial use, however homeowners may go to a hardware store or fungicide distributor for similar fungicides.
Sovran 50WG is registered for control of black rot. The Sovran label gives different use rates for control of different diseases. For black rot the rate is 3.2-4.8 oz/A. Sovran is excellent for control of black rot.
Flint 50WG is in the same general class of chemistry as Abound and Sovran. It is registered for the control of black rot,
powdery mildew
Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of ascomycete fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, as ...
and suppression of
downy mildew
Downy mildew refers to any of several types of oomycete microbes that are obligate parasites of plants. Downy mildews exclusively belong to the Peronosporaceae family. In commercial agriculture, they are a particular problem for growers of crucif ...
. For black rot the rate is 2.0 oz/A.
Abound is in the same general class of chemistry as Sovran and Flint (strobilurin). Abound is recommended at the rate of 11-15.4 fl oz/A. In university tests, the rate of 11-12 fl oz provided good control of the mentioned diseases above. Abound Flowable is very
phototoxic
Phototoxicity, also called photoirritation, is a chemically induced skin irritation, requiring light, that does not involve the immune system. It is a type of photosensitivity.
The skin response resembles an exaggerated sunburn. The involved chemi ...
to
apples
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...
of the variety
McIntosh
McIntosh, Macintosh, or Mackintosh (Gaelic: ') may refer to:
Products and brands
* Mackintosh, a form of waterproof raincoat
* Mackintosh's or John Mackintosh and Co., later Rowntree Mackintosh, former UK confectionery company now part of Nestl ...
or varieties related. Do not allow spray to drift from grapes to apples.
Pristine 38WDG contains a combination of two active ingredients (
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'', ...
, 12.8% and boscalid 25.2%).Pyraclostrobin, a
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 ...
, is in the same general class of chemicals as Abound, Sovran, and Flint (strobilurin Pristine is registered for use at the rates of 6-10.5 oz/A. A maximum of six applications may be made per season). The label states, “Do not use on
Concord
Concord may refer to:
Meaning "agreement"
* Pact or treaty, frequently between nations (indicating a condition of harmony)
* Harmony, in music
* Agreement (linguistics), a change in the form of a word depending on grammatical features of other ...
, Worden, Fredonia, or related varieties due to possible
foliar
A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
injury. Experience in New York suggests that
Corot noir
Corot noir is a Hybrid grape variety for use in red wine production. It was developed by grape breeder Bruce Reisch at the Cornell University New York State Agricultural Experiment Station The New York State Agricultural Experiment Station (NYSAE ...
and
Noiret
Noiret is a hybrid grape variety for use in red wine production. It was developed and named by Cornell University researchers working at the New York State Agricultural Experiment Station, and was officially released on July 7, 2006.
Description ...
may also be sensitive to Pristine.”
Black Rot Control for Organic Growers''
''Excerpt from Dr. Wayne Wilcox’s Grape Disease Notes, 2009 suggests a possible way for controlling black rot on grapes in
organic farming
Organic farming, also known as ecological farming or biological farming,Labelling, article 30 o''Regulation (EU) 2018/848 of the European Parliament and of the Council of 30 May 2018 on organic production and labelling of organic products and re ...
.''
Black rot is probably the
“Achilles heel” for organic grape production in the East. In the only good trial that we’ve run with
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) 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 pinkis ...
, it provided 40% disease control when applied at 2-week intervals, versus essentially 100% control with Nova. To try to avoid this, implement a rigorous program to remove mummies during pruning, and spray copper once a week throughout much of the growing season. This was hard on some of the hybrid vines and runs counter to the thinking of many with a “sustainable” orientation (after all, copper is an element and doesn’t break down into anything else, so it stays in the soil forever), but it did control the disease in an organically acceptable manner. Limit inoculum within the vineyard. Ideally, this would include removing or burying any mummies that you might encounter at the site. All mummified clusters should be removed from the trellis during pruning and from 2 to 6 weeks after cap fall and prune out any affected clusters before they allow the disease to spread, all the better (spores for disease spread are dispersed by rain primarily within 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 ...
, so should pose little risk of causing new infections if said clusters are simply dropped to the ground).
Notes
References
*
*
*
External links
Black Rot
{{DEFAULTSORT:Black Rot (Grape)
Botryosphaeriales
Fungal grape diseases
Fungi described in 1892