Coulure (pronounced coo-LYUR) is a

viticultural hazard This is a list of diseases of grapes (''Vitis'' spp.). Bacterial diseases Fungal diseases Miscellaneous diseases and disorders Nematodes, parasitic Phytoplasma, virus and viruslike diseases See also *'' Ampeloglypter ater'' *'' Am ...

that is the result of metabolic reactions to weather conditions that causes a failure of

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 a ...

s to develop after

flowering A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanism ...

. In English the word ''shatter'' is sometimes used. Coulure is triggered by periods of cold, cloudy, rainy weather or very high out-of-season temperatures. The condition is most often manifested in the

spring Spring(s) may refer to: Common uses * Spring (season) Spring, also known as springtime, is one of the four temperate seasons, succeeding winter and preceding summer. There are various technical definitions of spring, but local usage of ...

. It also occurs in vines that have little sugar content in their tissue.

Flowers A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanism ...

stay closed and are not

fertilized Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...

. Thus the vines are not

pollinated Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, a ...

as the grape fails to develop and falls off. Coulure can also cause irregular bunches of grapes which are less compact than normal. These bunches are more sensitive to developing various grape diseases. The yield of a vine with coulure will decrease substantially.

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 ...

with high proclivity to coulure are Grenache,

Malbec Malbec () is a purple grape variety used in making red wine. The grapes tend to have an inky dark color and robust tannins, and are known as one of the six grapes allowed in the blend of red Bordeaux wine. In France, plantations of Malbec are n ...

, Merlot, and

Muscat Ottonel Muscat Ottonel or Muskat-Ottonel (in Germany) is a white wine grape variety that is a member of the Muscat family of ''Vitis vinifera''.J. Robinson, J. Harding and J. Vouillamoz ''Wine Grapes - A complete guide to 1,368 vine varieties, including ...

. Other causes of coulure may be vineyard conditions and practices,

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, ...

too early or too severely, excessively fertile soils or overuse of

fertilizers A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...

, and improper selection of

rootstocks A rootstock is part of a plant, often an underground part, from which new above-ground growth can be produced. It could also be described as a stem with a well developed root system, to which a bud from another plant is grafted. It can refer to a ...

clones Clone or Clones or Cloning or Cloned or The Clone may refer to: Places * Clones, County Fermanagh * Clones, County Monaghan, a town in Ireland Biology * Clone (B-cell), a lymphocyte clone, the massive presence of which may indicate a pathologi ...

.J. Robinson (ed) ''"The Oxford Companion to Wine"'' Third Edition pg 207-208 Oxford University Press 2006 During the flowering part of the growing season (May-June in the Northern Hemisphere, November-December in the Southern Hemisphere), grapevines often need dry conditions with sufficient sunlight and ambient air temperature around for pollination to go smoothly. Less ideal conditions, particularly wet, rainy weather, increases the odds that a higher than normal numbers of flowers go unpollinated and coulure to occur.Wine & Spirits Education Trust ''"Wine and Spirits: Understanding Wine Quality"'' pg 25, Second Revised Edition (2012), London, Coulure is a distinct phenomena unrelated to another viticultural hazard,

millerandage Millerandage (or shot berries, hens and chicks and pumpkins and peas) is a potential viticultural hazard problem in which grape bunches contain berries that differ greatly in size and, most importantly, maturity. Its most common cause is cold, rain ...

, where the flowers are pollinated but the resulting berries develop without seeds and remain small. Like coulure, millerandage is often caused by inclement weather during the flowering and fruit set period and cause reduced yields.

Cause and effect

Coulure is caused by a

carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or m ...

deficiency in the plant tissues that causes the vine to conserve resources that would otherwise be funneled into the developing grape berries. As carbohydrate levels drop, soon after flowering the stems connected to the berries shrivel as the small grapes (0.2 inches/5 millimeters in diameter) eventually fall off. To some extent coulure and the dropping of fruit is a natural and healthy reaction of a vine that is self-regulating its resource and the amount of fruit that it produces. But when the situation is exacerbated by certain weather conditions and disruption to

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

, coulure can have a more severe impact on yields that may negatively affect a region's grape supply and thus influence pricing. When the weather is the primary instigator of coulure, the French term this phenomenon ''coulure climatique''. This describes the cloudy and wet conditions that limit the amount of photosynthetic activity that takes place during the flowering cycle of a grapevine. Limited sunshine means lower sugar levels that can be converted into resources to develop grape berries. Warm temperatures can also exacerbate coulure in some grape varieties by promoting

cellular respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

and excessive

shoot In botany, a plant shoot consists of any plant stem together with its appendages, leaves and lateral buds, flowering stems, and flower buds. The new growth from seed germination that grows upward is a shoot where leaves will develop. In the sp ...

growth that further competes with the berries for the resources derived from carbohydrates. Other contributing factors include excessively fertile

vineyard soils The soil composition of vineyards is one of the most important viticultural considerations when planting grape vines. The soil supports the root structure of the vine and influences the drainage levels and amount of minerals and nutrients that the ...

, either naturally or enhanced by the use of

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

-rich fertilizers, overly vigorous rootstock and severe pruning that too drastically limits the amount of leaf surface needed to sustain photosynthesis.

Prevention

Coulure is not 100% preventable but a vineyard manager can take several precautions to lessen the severity and impact of coulure. Some grape varieties are more prone to develop coulure than others, such as Grenache,

, Merlot and

. A grower can choose to grow clones of those varieties, now commonly available for Merlot and Malbec, that have less susceptibility to developing coulure. In the vineyard, care can be taken to not prune so severely and insure that there is adequate leaf coverage for photosynthesis. Trimming the tips of developing shoots near the end of the flowering period can lessen the competition for sugar resources between berries and new shoot development. For non- organic viticulture, chemical growth inhibitors can be applied to the vine to limit shoot growth as well.

References

External links

Epicurious.com
{{Viticulture Oenology Grape diseases