FROST PROTECTION" IN" LEMON" ORCliARDS. 



Adequate provision was made in all the protected orchards in 

 which these studies were conducted for refilling the heaters from 

 storage reservoirs, such as the one shown in figure 4, and for their 

 continuous care during the frosts. One of the methods used for 

 distributing the oil is shown in figure 5. It can be safely said that 

 in the orchards under observation the maximum efficiency of the 

 heaters was obtained during the cold periods. 



OBJECTS OF THE INVESTIGATIONS. 



The effect of the low temperatures upon the lemon trees in non- 

 heated orchards was very noticeable immediately following the freeze. 

 The trees in non- 

 heated orchards were 

 partially or com- 

 pletely defohated, as 

 shown in Plates I 

 and II. The trees in 

 heated orchards did 

 not show this con- 

 dition to any marked 

 extent except in the 

 upper branches, 

 where the leaves were 

 blown off by the 

 violent winds which 

 accompanied the low 

 temperatures, as 

 shown in Plate III. 

 In the nonheated or- 

 chards in many in- 

 stances the bark on 

 the branches and, in 

 some cases, on the 

 trunk of the trees, 

 was split more or less 

 severely. Often it 

 was necessary to cut 



off these injured branches during the spring months following the 

 low temperatures, in order to aid the trees in recovering from frost 

 injury. In nearly all cases where trees were defohated it was 

 found desirable to whitewash the trunks and main branches, in 

 order to protect the trees from further injury by exposure to the sun. 

 It was therefore possible, in a general way, to determine the amount 

 of immediate injury to the trees themselves. 



Fig. 3. — Heaters in position for use in a Corona lemon orchard. The 

 heaters are usually set on a small board or other support in order to 

 avoid as far as possible damage from rust due to contact ^\•ith the soil. 

 Great care must be used in order to prevent leakage from the heat- 

 ers, as even small quantities of oil in orchard soils have been found to 

 be injurious to the trees. As soon as the cold weather is over, the pots 

 are usually removed from the orchard, emptied, cleaned, coated vrith 

 hot oil, and stored for the summer. 



