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In spite of the fact that we are supposed to be in the rainy season, signs of water stress are appearing on lawns around the island. The few rain storms we have been lucky enough to get this month disappeared fairly quickly due to our sandy soil.

A good example of this process is how quickly the rain waters recede from our area roads. If you turn your sprinklers off after one of these rain storms be sure to turn them back on if there are no more soaking rains within four or five days. This is especially important if you have new sod in areas damaged by the spring drought. This sod has very shallow roots. Water is needed in large quantities by a lawn. And it's required more frequently in the summer than during the winter.

Water comprises 80 to 90 percent of the fresh weight of grass and it also plays a fundamental role in the plant metabolism. Only one percent of water absorbed by plants is utilized for metabolic activity. The majority of water absorbed is used for transpiration. This is a plant process in which water is absorbed by the roots, passed through the vascular system, and exited from the plant via the stomata into the atmosphere.

Transpiration helps maintain plant temperatures by cooling through the latent heat of vaporization. The water absorbed by the plants in the transpiration process also brings nutrients from the soil into the plant. The amount of water transferred into the atmosphere by evapotranspiration from turf surfaces is governed by a number of environmental factors. Sunlight, relative humidity, temperature, wind and available soil moisture are all controlling elements.

Minimal ET rates occur when there are dark, cloudy days with high relative humidity, low temperatures and no wind. Maximum ET rates occur on bright sunny days with low humidity, high temperatures and high winds. According to a table computed by the United States Department of Agricultural Soil Conservation Service June through September have the highest evapotranspiration rates. This means these months also have high irrigation requirements.

Don't be misled by light summer rain showers. Often these rains only wet the soil surface and evaporate rapidly. A general rule used in Florida is to apply three-fourths to 1 inch of water one to two times a week in summer. It's true that too much water can cause damage just like too little water. Most people do not pay close enough attention to their lawns to allow for the "Water on Wilt" method. The result is a lawn which goes into water stress when too little water is applied during periods when we don't have adequate rainfall.

This results in populations of chinch bugs in the dry areas and the need to apply more insecticides to prevent damage. The best remedy is to have a rain-stat installed. It will pay for itself the first summer you install it.

Installed on the edge of the house, it is a device that is wired to the sprinkler timer and will automatically turn the system off when there has been adequate rainfall. As the wick dries (as the soil would dry) it allows the system to run again. These devices are required by law on all houses.

Every home should have one. Call your sprinkler repair company and have a rain stat installed today.

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Eileen Ward and her husband, Peter, own and operate Greensward of Marco Inc., a lawn maintenance and landscaping company. Besides completing horticultural courses from the University of Florida, she has a commercial maintenance spray license and is a registered dealer in agricultural products in Florida. To reach Ward, call 394-1413.