26 



Farmers' Bulletin 1096. 



tremely heavy frosts, like those of 1913 in California, are to be fought 

 successfully, dependence should not be placed on a much smaller 

 number. Some growers have successfully protected their orange 

 crops for several years with as few as 30 or 40 heaters to the acre, 

 but no exceptionally heavy frosts occurred during that time. (See 

 figs. 13 and 14.) 



Lemons are more susceptible to frost damage than oranges, but 

 where a large acreage is protected it is usually possible to save the 

 large fruit with 100 large capacity heaters to the acre when the tem- 

 perature falls to 19. A portion of the blossoms and young fruit is 

 likely to be frozen when the temperature remains at this point for five 

 or six hours, even with 100 heaters to the acre. 



Care of Oil Heaters. The amount of attention given to storage 

 and care of oil heaters varies greatly in different parts of the country. 

 In parts of California where the annual rainfall is light, many fruit 

 growers leave the heaters in the orchards during the entire year, 



8f>M 9PM. JOf>M. J/P.M 



SAM MM 4/t.M SAM 



M. 7/4M SAM. 30., 



'I .1 



Temperature of cnec/r statxn, not /nfA/enced ty f/r/ng. 



Temperature at stat/on H. 



___ Temperature at station C 

 Heaters /grr/ted 



FIG. 11. Continuous records of the temperature at stations H and C in figure 10 and at 

 a third station located in an unheated orchard about 500 yards to the southeast. 

 When the fires were lighted at station H about 10 p. m., the wanned air drifting 

 across to station C raised the temperature there almost as much as at station H inside 

 the fired area. At the end of the season the fruit at station C was in better condition 

 than that at station H, due to the protection afforded by the firing in the neighboring 

 grove. Note that the temperature at stations H and C ran nearly 2 lower than at the 

 third station before the fires were lighted. 



setting them up close to the trunks of the trees affer the danger of 

 frost is past. Trees are sometimes injured or even killed through oil 

 from leaky heaters penetrating the soil around the roots. For this 

 reason, heaters left in the orchard should be emptied at the end of 

 the season. Lard-pail heaters are usually covered with a film of 

 oil, which helps to prevent rusting, and the rate of deterioration is 

 little, if any, greater than is the case when they are stored under 

 cover. Where there is considerable annual rainfall, lard-pail heaters 

 should be emptied, dipped in heavy oil, and stored under cover when 

 not in use. With ordinary care heaters of this type will last 10 

 years or longer. Several orchardists have used them 14 and even 16 

 years without losing more than a small percentage through deteriora- 



