Insects, Diseases and Frost 283 



Smudging and heating. 



The object of smudging is to produce a cloud of smoke 

 which will prevent the radiation of heat from the earth ; 

 the object of heating is actually to warm the air. These 

 methods find favor in districts where no mulch is used, 

 especially in the Pacific Northwest. They are most 

 effective when the area to be protected is large and the 

 land approximately level. On hilly land the cold air 

 settles down under the smudge cloud from higher points 

 and pushes it upward. 



Piles of dry kindling are covered with wet straw, manure, 

 corn cobs or sawdust, and are lighted with kerosene ; if 

 coal tar is poured over the fires, the smoke is denser. The 

 distance between piles on the outside of the field should 

 not be less than seventy-five feet, especially on the wind- 

 ward side, but may be less inside the field. 



In recent years, heating has largely superseded smudg- 

 ing. There are a number of types of patented heaters; 

 most of these bum crude oil, but some burn coal. At 

 least 100 heaters are required to protect an acre. The 

 expense of this method is $20 to $50 an acre a season. It 

 is useless to begin without a large supply of oil to replen- 

 ish the heaters. In 1910 Charles Staib, of Missouri, 

 reported : ^ "The experiments taught us that we need 125 

 to 150 pots per acre to protect the bloom and berries fully 

 from a frost of 24 degrees above zero. One hundred 

 heaters per acre raise the temperature five degrees. The 

 cost per acre for 100 heaters, besides labor, was $20 for 

 heaters and $15.14 for oil. The temperature went to 

 24 degrees outside the field. Where we used 100 heaters 

 the yield was 245 crates per acre which sold for $551.25 

 gross. Where no heaters were used, the yield was 96.6 



1 Kept. Mo. St. Bd. Hort., 1910, pp. 47-9. 



