WEATHER IN CRANBERRY CULTURE 61 



earth. "^ This causes the air near the surface over a grass cover to be colder on 

 frosty nights than it is over bare soil. It would therefore be helpful to keep the 

 land around bogs, especially small ones, plowed and free of vegetation, for the 

 air draining onto the bogs from the slopes of the uplands would be somewhat 

 warmer on cold nights. ^^ This would also reduce the number of cranberry girdlers 

 and spittle insects that come onto the bogs from the uplands, by removing their 

 food plants from around the margins. Experience alone can tell how well these 

 advantages will pay for the trouble and expense involved. 



Moss 



Both hair-cap and sphagnum moss greatly restrict the warming of the ground 

 by the sun and the transfer of heat from the soil to the air on cold nights.''^ Their 

 removal from cranberry bogs, therefore, helps to prevent frosts. Resanding 

 tends to smother moss, but it may form an insulating felt under the sand. Hair- 

 cap moss may be killed with a spray of 20 pounds of copper sulfate in 100 gallons 

 of water, applied at the rate of 600 gallons an acre, preferably early in the spring. 



Fallen Leaves 



Thick accumulations of fallen cranberry leaves, like moss, greatly restrict the 

 flow of heat into and from the soil and form an insulating layer when covered 

 with sand. The leaves cannot be removed from dry bogs very well, but flooding 

 brings them to bog margins freely and they should always be taken from the 

 water there. ''^ 



Defrosting with Water 



Growers sometimes suggest spraying frosted cranberry bogs with water before 

 sunrise to avert injury. The writer and others have tried this and the spray has 

 always increased the injury greatly. 



Chemicals 



The effects of chemical applications on cranberry frosts and their results 

 have not been studied, but they are not used with other crops and probably 

 would have little value. 



Wind Machines 



As the air overhead is commonly warmer on frosty nights than that near the 

 ground, blowers have been used extensively in the West, especially in citrus or- 

 chards, to mix it with the lower air and so prevent frost. Some cranberry growers 

 on the Pacific coast think they are useful, over 100 acres of bog being serviced with 

 them. Their value for bog protection has been tested at the experiment station 

 at East Wareham.*" In the West, smt 11 machines are not effective beyond 300 

 feet and large ones beyond 500 feet.^i Observations in California and at East 



^^Brooks, F. A., Solar energy and its use for heating water in California, Calif. Agr. Expt. Sta. 

 Bui. 602, 1936, p. 18. (Copy in the Middleboro library.) 



"This advantage probably would often be increased if the plowed land were wet down thor- 

 oughly before frosts. 



^^Cox, op. cit., p. 44. 



■^^Mass. Agr. Expt. Sta. Bui. 371. 1940, p. 22. (Copies in the Middleboro library.) 



^''Professor C. I. Gunness, head of the department of engineering, did most of this work. 



^'Schoonover, Brooks, and Walker, op. cit., p. 21. 



