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Growing degree days (GDD), also called growing degree units (GDUs), are a
heuristic A heuristic (; ), or heuristic technique, is any approach to problem solving or self-discovery that employs a practical method that is not guaranteed to be optimal, perfect, or rational, but is nevertheless sufficient for reaching an immediate, ...
tool in
phenology Phenology is the study of periodic events in biological life cycles and how these are influenced by seasonality, seasonal and interannual variations in climate, as well as environmental factor, habitat factors (such as elevation). Examples includ ...
. GDD are a measure of heat accumulation used by
horticulturists Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprouts, mushrooms, algae, flowers, seaweeds and no ...
,
gardener A gardener is someone who practices gardening, either professionally or as a hobby. Description A gardener is any person involved in gardening, arguably the oldest occupation, from the hobbyist in a residential garden, the home-owner suppleme ...
s, and
farmer A farmer is a person engaged in agriculture, raising living organisms for food or raw materials. The term usually applies to people who do some combination of raising field crops, orchards, vineyards, poultry, or other livestock. A farmer mig ...
s to predict plant and animal development rates such as the date that a
flower 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 mechani ...
will bloom, an insect will emerge from dormancy, or a
crop A crop is a plant that can be grown and harvested extensively for profit or subsistence. When the plants of the same kind are cultivated at one place on a large scale, it is called a crop. Most crops are cultivated in agriculture or hydroponic ...
will reach maturity.


Introduction

In the absence of extreme conditions such as unseasonal
drought A drought is defined as drier than normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D.  Jiang, A.  Khan, W.  Pokam Mba, D.  Rosenfeld, J. Tierney, an ...
or disease, plants grow in a cumulative stepwise manner which is strongly influenced by the ambient temperature. Growing degree days take aspects of local
weather Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the ...
into account and allow gardeners to predict (or, in
greenhouse A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of Transparent ceramics, transparent material, such as glass, in which plants requiring regulated climatic condit ...
s, even to control) the plants' pace toward maturity. Unless stressed by other environmental factors like moisture, the development rate from emergence to maturity for many plants depends upon the daily air temperature. Because many developmental events of plants and insects depend on the accumulation of specific quantities of heat, it is possible to predict when these events should occur during a growing season regardless of differences in temperatures from year to year. Growing degrees (GDs) is defined as the number of temperature degrees above a certain threshold base temperature, which varies among crop species. The base temperature is that temperature below which plant growth is zero. GDs are calculated each day as maximum temperature plus the minimum temperature divided by 2, minus the base temperature. GDUs are accumulated by adding each day's GDs contribution as the season progresses. GDUs can be used to: assess the suitability of a region for production of a particular crop; estimate the growth-stages of crops, weeds or even life stages of insects; predict maturity and cutting dates of forage crops; predict best timing of fertilizer or pesticide application; estimate the heat stress on crops; plan spacing of planting dates to produce separate harvest dates. Crop specific indices that employ separate equations for the influence of the daily minimum (nighttime) and the maximum (daytime) temperatures on growth are called crop heat units (CHUs).


GDD calculation

GDD are calculated by taking the integral of warmth above a base temperature, ''T''base (plant type dependant, see baseline section): :GDD = \int(T(t) - T_\mathrm)dt (where integration is over the time period with T(t) > T_\mathrm). A simpler, approximately equivalent formulation uses the average of the daily maximum and minimum temperatures compared to a ''T''base. As an equation: :GDD = \frac-T_\mathrm. If the minimum temperature ''T''min is below the ''T''base one, there exist two variants: * variant A: Do not change T_\mathrm. Only if (T_\mathrm+T_\mathrm)/2 < T_\mathrm, set (T_\mathrm+T_\mathrm)/2 = T_\mathrm . The resulting GDD is 0. This can be written more compactly as: GDD = \max * variant B: Change T_\mathrm to T_\mathrm=T_\mathrm GDDs are typically measured from the winter low. Any temperature below ''T''base is set to ''T''base before calculating the average. Likewise, the maximum temperature is usually capped at 30 °C because most plants and insects do not grow any faster above that temperature. However, some warm temperate and tropical plants do have significant requirements for days above 30 °C to mature fruit or seeds.


Example of GDD calculation

For example, a day with a high of 23 °C and a low of 12 °C (and a base of 10 °C) would contribute 7.5 GDDs. :\frac-10=7.5 As a second example, a day with a high of 13 °C and a low of 5 °C (and a base of 10 °C) would contribute: * version A: 0 GDD, as: \max((13+5)/2- 10, 0)=0) * version B: 1.5 GDDs, as: (13+10)/2-10=11.5-10=1.5


Plant development


Pest control

Insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...
development and growing degree days are also used by some
farmer A farmer is a person engaged in agriculture, raising living organisms for food or raw materials. The term usually applies to people who do some combination of raising field crops, orchards, vineyards, poultry, or other livestock. A farmer mig ...
s and
horticulturalist Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprouts, mushrooms, algae, flowers, seaweeds and no ...
s to time their use of organic or
biological pest control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...
or other
pest control Pest control is the regulation or management of a species defined as a pest; any animal, plant or fungus that impacts adversely on human activities or environment. The human response depends on the importance of the damage done and will range ...
methods so they are applying the procedure or treatment at the point that the pest is most vulnerable. For example: *
Black cutworm ''Agrotis ipsilon'', the dark sword-grass, black cutworm, greasy cutworm, floodplain cutworm or ipsilon dart, is a small noctuid moth found worldwide. The moth gets its scientific name from black markings on its forewings shaped like the letter " ...
larvae have grown large enough to start causing economic damage at 165 GDD * Azalea lace bug emerges at about 130 GDD * Boxwood leafminer emerges at about 250 GDD


Honeybees

Several
beekeeper A beekeeper is a person who keeps honey bees. Beekeepers are also called honey farmers, apiarists, or less commonly, apiculturists (both from the Latin '' apis'', bee; cf. apiary). The term beekeeper refers to a person who keeps honey bees i ...
s are now researching the correlation between growing degree-days and the life cycle of a
honeybee A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the current cosmo ...
colony.


Baselines

The optimal base temperature is often determined experimentally based on the life cycle of the plant or insect in question. Common baselines for crops are either 5 °C for cool-season plants and 10 °C for warm-season plants and most insect development.


Crops

* 4.5 °C
wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
,
barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley pr ...
, rye,
oat The oat (''Avena sativa''), sometimes called the common oat, is a species of cereal grain grown for its seed, which is known by the same name (usually in the plural, unlike other cereals and pseudocereals). While oats are suitable for human con ...
s,
flaxseed Flax, also known as common flax or linseed, is a flowering plant, ''Linum usitatissimum'', in the family Linaceae. It is cultivated as a food and fiber crop in regions of the world with temperate climates. Textiles made from flax are known in W ...
,
lettuce Lettuce (''Lactuca sativa'') is an annual plant of the family Asteraceae. It is most often grown as a leaf vegetable, but sometimes for its stem and seeds. Lettuce is most often used for salads, although it is also seen in other kinds of food, ...
,
asparagus Asparagus, or garden asparagus, folk name sparrow grass, scientific name ''Asparagus officinalis'', is a perennial flowering plant species in the genus ''Asparagus''. Its young shoots are used as a spring vegetable. It was once classified in ...
,"
canning Canning is a method of food preservation in which food is processed and sealed in an airtight container (jars like Mason jars, and steel and tin cans). Canning provides a shelf life that typically ranges from one to five years, although u ...
purposes" * 8 °C
sunflower The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as ...
,
potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Unit ...
* 10 °C
maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. Th ...
(including sweet corn),
sorghum ''Sorghum'' () is a genus of about 25 species of flowering plants in the grass family (Poaceae). Some of these species are grown as cereals for human consumption and some in pastures for animals. One species is grown for grain, while many othe ...
,
rice Rice is the seed of the grass species ''Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima ''Oryza glaberrima'', commonly known as African rice, is one of the two domesticated rice species. It was first domesticated and grown i ...
,
soybeans The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu and ...
,
tomato The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...
,
coffee Coffee is a drink prepared from roasted coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulant, stimulating effect on humans, primarily due to its caffeine content. It is the most popular hot drink in the world. S ...
,Jaramillo R., A. and Guzman M., O. Relationship between temperature and growth in ''Coffea arabica'' L. var. Caturra. Cenicafé (Colombia) 35(3):57-65. 1984.
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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, ...
s,
snap bean Green beans are young, unripe fruits of various cultivars of the common bean (''Phaseolus vulgaris''), although immature or young pods of the runner bean (''Phaseolus coccineus''), yardlong bean ( ''Vigna unguiculata'' subsp. ''sesquipedalis' ...
s,
lima bean A lima bean (''Phaseolus lunatus''), also commonly known as the butter bean, sieva bean, double bean, Madagascar bean, or wax bean is a legume grown for its edible seeds or beans. Origin and uses ''Phaseolus lunatus'' is found in Meso- and Sou ...
s * 30 °C the
USDA The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of com ...
measure heat zones in GDD above 30 °C; for many plants this is significant for seed maturation, e.g.
reed Reed or Reeds may refer to: Science, technology, biology, and medicine * Reed bird (disambiguation) * Reed pen, writing implement in use since ancient times * Reed (plant), one of several tall, grass-like wetland plants of the order Poales * ...
(''Phragmites'') requires at least some days reaching this temperature to mature viable seeds


Pests

* 6 °C Stalk borer * 7 °C
Corn rootworm ''Diabrotica'' is a large, widespread genus of beetles in the family Chrysomelidae. Members of this genus include several destructive agricultural pest species, sometimes referred to as cucumber beetles or corn rootworms. Species * '' Diabroti ...
* 9 °C
Alfalfa weevil ''Hypera postica'', commonly known as the alfalfa weevil, is a species of beetle in the superfamily Curculionoidea; it can be found in alfalfa fields throughout Europe. Considered a destructive threat to alfalfa production in North America, sev ...
* 10 °C
Black cutworm ''Agrotis ipsilon'', the dark sword-grass, black cutworm, greasy cutworm, floodplain cutworm or ipsilon dart, is a small noctuid moth found worldwide. The moth gets its scientific name from black markings on its forewings shaped like the letter " ...
,
European corn borer The European corn borer (''Ostrinia nubilalis''), also known as the European corn worm or European high-flyer, is a moth of the family Crambidae which includes other grass moths. It is a pest of grain, particularly maize (''Zea mays''). The in ...
, standard baseline for insect and mite pests of woody plants * 11 °C Green cloverworm


Modified growing degree days

In the cases of some plants, not only do they require a certain minimum temperature to grow, but they will also stop growing above a warmer threshold temperature. In such cases, a ''modified growing degree day'' is used: the growing degree days are calculated at the lower baseline, then at the higher baseline, which is subtracted.
Corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. Th ...
is an example of this: it starts growing at 10 °C and stops at 30 °C, meaning any growing degree-days above 30 °C do not count.


Units

GDDs may be calculated in either Celsius or Fahrenheit, though they must be converted appropriately; for every 9 GDDF there are 5 GDDC, or in conversion calculation: GDDC = 5/9 * GDDF The equivalent unit compliant with the International System of Units is the
kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phys ...
-
second The second (symbol: s) is the unit of time in the International System of Units (SI), historically defined as of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds ...
. A quantity of kelvin-seconds is four
orders of magnitude An order of magnitude is an approximation of the logarithm of a value relative to some contextually understood reference value, usually 10, interpreted as the base of the logarithm and the representative of values of magnitude one. Logarithmic dis ...
higher than the corresponding degree day (1 Celsius degree-day is 8.64×104 K·s; 1 Fahrenheit degree-day is 4.8×104 K·s).


See also

*
Degree day A degree day is a measure of heating or cooling. Total degree days from an appropriate starting date are used to plan the planting of crops and management of pests and pest control timing. Weekly or monthly degree-day figures may also be used wi ...
*
Growing season A season is a division of the year marked by changes in weather, ecology, and the amount of daylight. The growing season is that portion of the year in which local conditions (i.e. rainfall, temperature, daylight) permit normal plant growth. Whil ...
*
Heating degree day Heating degree day (HDD) is a measurement designed to quantify the demand for energy needed to heat a building. HDD is derived from measurements of outside air temperature. The heating requirements for a given Architectural structure, building at ...
*
Weather derivative Weather derivatives are financial instruments that can be used by organizations or individuals as part of a risk management strategy to reduce risk associated with adverse or unexpected weather conditions. Weather derivatives are index-based instr ...
*
Winkler scale The Winkler Index, sometimes known as the Winkler Scale or Winkler Regions, is a technique for classifying the climate of wine growing regions based on heat summation or growing degree-days. In the system, geographical areas are divided into five c ...
*
Phenology Phenology is the study of periodic events in biological life cycles and how these are influenced by seasonality, seasonal and interannual variations in climate, as well as environmental factor, habitat factors (such as elevation). Examples includ ...


References

404 link


Notes

{{reflist


External links


Good explanation of Growing Degree Day calculations with examples

Current year-to-date GDDs for selected US cities



GDDs to various stages of maturity for selected crops


* ttps://web.archive.org/web/20081201050049/http://www.guaranteedweather.com/content_page.aspx?content_id=48 Online GDD calculator
Turf Growing Degree Days Calculator for sports stadia and golf courses
Climatology Horticulture Agrometeorology Pest control Seasons Meteorological indices