below the Tbase one, there exist two variants: variant A: Do not change . Only if , set . The resulting GDD is 0. This can be written more compactly as: variant B: Change to GDDs are typically measured from the winter low. Any temperature below Tbase is set to Tbase 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. 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: ) version B: 1.5 GDDs, as: Plant development Pest control Insect development and growing degree days are also used by some farmers and horticulturalists to time their use of organic or biological pest control or other pest control methods so they are applying the procedure or treatment at the point that the pest is most vulnerable. For example: Black cutworm 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 beekeepers are now researching the correlation between growing degree-days and the life cycle of a honeybee 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, barley, rye, oats, flaxseed, lettuce, asparagus,"canning purposes" 8 °C sunflower, potato 10 °C maize (including sweet corn), sorghum, rice, soybeans, tomato, coffee, grapes, snap beans, lima beans 30 °C the USDA measure heat zones in GDD above 30 °C; for many plants this is significant for seed maturation, e.g. reed (Phragmites) requires at least some days reaching this temperature to mature viable seeds Pests 6 °C Stalk borer 7 °C Corn rootworm 9 °C Alfalfa weevil 10 °C Black cutworm, European corn borer, standard baseline for insect