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 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-second. A quantity of kelvin-seconds is four orders of magnitude 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 Growing season Heating degree day Weather derivative Winkler scale Phenology References 404 link Notes External links Good explanation of Growing Degree Day calculations with examples Current year-to-date GDDs for selected US cities a table of GDDs necessary for grapes GDDs to various stages of maturity for selected crops University of Massachusetts Amherst Extension, Integrated Pest management Tools, web site accessed Jan 2005 Online GDD calculator Turf Growing Degree Days Calculator for sports stadia and golf courses Climatology Horticulture Agrometeorology Pest control Seasons Meteorological indices