growers used various ingenuous methods to determine the starting time. The 

 most common method was to observe and feel the formation of ice crystals on 

 the leaves in the lower part of the strawberry field. Other growers parked 

 their cars in a low area and watched for the formation of frost on roof and 

 fenders. One grower used an old car fender placed in the lowest area while 

 another used a very thin layer of water in a pie plate which was set directly 

 on the row. It should be noted, however, although frosts are usually accom- 

 panied by deposition of ice crystals, that temperatures below 32° F. may 

 occur without the formation of ice crystals. This condition is known as 

 "black frost" and may result in frozen plants. 



To avoid risks thermometers should be used. These should be placed at 

 plant level because temperature here is apt to be several degrees colder than 

 at four or five feet above the ground. The use of temperature - alarm devices 

 can save growers a great deal of sleep. 



A sprinkler irrigation system, if properly used is the most effective 

 method known to control, or greatly reduce damage caused by frost. Smudge 

 pots or burning tires work only on those rare nights when atmospheric condi- 

 tions are just right. In many cases frost protection is obtained for a 

 short distance only from the smudge pots or burning tires. 



Irrigation equipment can be placed to cover more area when used for 

 frost protection than when used for irrigation. Many irrigation systems are 

 designed so that water from one sprinkler will reach the base of the next 

 sprinkler. For frost protection, the spacing of the sprinklers can be 

 increased to cover about twice as much area. It is suggested in the Michigan 

 State University Extension Bulletin #327 that for frost protection, the wetted 

 area from one sprinkler should overlap for a few feet the wetted area from the 

 next sprinkler. To distribute the water satisfactorily over a large area 

 sprinklers should be spaced in a triangular pattern instead of a rectangular 

 or square pattern. 



Sprinklers with smaller nozzles than those used for protection against 

 drought are more efficient in frost protection, as generally ice is formed 

 more quickly than with large nozzle sprinklers. 



The Michigan State University Extension Bulletin gives the following 

 suggestions for using the irrigation equipment: 



"The water distribution in the field should be checked to make sure that 

 all the plants are sprinkled with enough water. This can be done by measuring 

 the water depth in several oil cans--with tops cut out — placed midway between 

 two sprinklers, where the water application is likely to be the least. This 

 should be done as a "test run" before the equipment is used for frost pro- 

 tection. 



The water application rate for frost protection should be just enough 

 to prevent damage to the plant. Putting on more water than is needed is a 

 waste of water and power, and may lead to waterlogging the soil. A minimum 

 water application rate of about 1/10 to 1/8 of an inch per hour, as measured 



