Principles of Freeze Protection for Fruit Crops

For a long time Alabama as well as much of the rest of the United States was provided with specific agricultural forecasts by the National Weather Service (NWS). However, in April, 1996 in a budget cutting move, the NWS closed all of its agricultural weather service centers including the one located at Auburn University. As a result, growers who desire specific agricultural weather information must now subscribe to one of two private agricultural weather firms, one located in Auburn, AL and the second in the Northeast. Some growers have contracted with private meteorologists for weather information.

The NWS continues providing similar forecasts to what has been provided in past years, but this information is of a general type and is not intended for direct agricultural application. The NWS Birmingham office serves most of Alabama while the Mobile office serves several southeastern counties. Weather information from NWS can be obtained by NOAA radio, special bulletins via TV and radio, newspaper and the internet. General weather forecasts and current conditions are always available via TV and internet links provided by special weather channels and local TV stations.

Frost/Freeze warnings are issued by the National Weather Service according to forecast conditions. Table 1 explains how the wording of these warnings should be interpreted. The type of warning given will assist the grower in understanding which if any of his freeze protection methods may be effective. For example, a "Freeze" warning implies that winds may be too high for successful use of helicopters, wind machines or overhead irrigation.

Until April of 1996, Alabama's Agricultural Weather Program at Auburn University was providing over 900 individual weather products via the internet. Part of this information was originating from 15 remote weather stations located strategically throughout the state. Currently some 15 remote stations are supplying weather information (Table 2). Previously, each of these stations supplied hourly (real time) information that was made available via internet to anyone and via specific networks to university workers. Today, only information for the past 30 days and the past 24 hours (ending at 7 AM each morning) is available via the internet or internal university networks. Presently growers can only access this information via the internet through a private firm. Efforts are being made to enable growers to access real time information from the remote weather stations as could be done previously via internet or bulletin board. A voice modem that provides real time information for growers is being currently operated at one of the remote weather stations.

Growers are reminded that forecasts by the NWS are generally based on temperatures for warmer, urban areas. Many of the locations are for airports where temperatures are almost always warmer than surrounding areas. The more rural farm areas most often experience temperatures during freeze events that are three to six degrees colder than forecasts. In some cases, the very coldest locations in an area may be as much as eight to ten degrees colder than the forecast. It is also possible to have frosts in rural areas when temperature forecast for urban areas are for mid to high 30's with no frost.

When using forecasts, no matter who is issuing them, it is always wise to continue relying on the updated, latest forecast for the freeze event. In addition, it is worth noting that forecasts are given for temperatures in an area at the 5-foot height. On calm nights, temperatures at the soil surface may be several degrees below those at the 5-foot height. This is especially applicable to crops such as strawberries that are located on the soil surface.

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