Normal GDD Northeast
Corn tassels, USDA photo
Image by Scott Bauer

Grow better corn using GDD.

Growing Degree Days (GDD)

Insects are dependent on temperature to develop. Data to initiate a pest control strategy based on air temperature is collected and reported from March 1 through September 30. This is the climatological calendar used under the Cornell system for woody tree and shrub insect pests. The accumulated GDD for various locations on Long Island are reported below.

In addition to the GDD Report utilizing daily air temperatures a GDD Report utilizing soil temperatures at 2 inch and 4 inch depths is also provided.

Some horticulture industries on Long Island (i.e. the LI Grape Industry) utilize GDD data later than September 30. For this reason GDD data is collected and an extended report is provided through October 31 for those individuals.

If you would like more information on utilizing Growing Degree Days (GDD) follow the link to the online fact sheet titled Using Growing Degree Days for Insect Pest Management.


Many growers of horticultural crops monitor precipitation on their farms, but precipitation does vary widely depending where you are located on Long Island. Members of the arboricultural, landscaping and irrigation industries servicing customers over a wide range of Suffolk County realized how varied precipitation rates can be from any one rain event. It is important for homeowners to be aware of the rate of precipitation in their area to help determine the need for supplemental irrigation on their lawns, landscapes and gardens. In a response to their needs Cornell Cooperative Extension – Suffolk County started providing daily precipitation rates. In 2006 we started providing evapotranspiration rates (ET) as well. Both precipitation and ET can be used as a guide for determining when supplemental irrigation needs to be applied to crops, landscape trees and shrubs and lawns on Long Island.

Evapotranspiration (ET)

A simple definition of ET would be that it is the process by which water is discharged to the atmosphere as a result of evaporation (water converted to a vapor) from the soil and transpiration (water that evaporates primarily through stomates in the leaves) by plants.

Plants put down roots into the soil to draw water and nutrients up into the stems and leaves. Some of this water is returned to the air by transpiration. Transpiration rates vary widely depending on weather conditions, such as temperature, humidity, sunlight availability and intensity, precipitation, soil type and saturation, wind, and land slope. During dry periods, transpiration can contribute to the loss of moisture in the upper soil zone, which can have an effect on vegetation and food-crop fields.

Knowing the rate of ET can help growers and homeowners determine the potential need to apply water to plants in their fields or landscapes. The ET rates and the amount of precipitation for various locations on Long Island in the reports in the left sidebar.


To sign up for emailed Growing Degree Day reports or to report errors:


Sandra Vultaggio
Horticulture Consultant

Last updated June 13, 2024