74 



To calculate for A, total leaf surface area per tree, the follow- 

 ing formula was needed (Turrell, 1961): 

 Log A = C^ + N^ log a. 

 Constants 



C = .994 on Valencia 

 N = 1 .068 on Valencia 

 Variables 



a - age of tree 

 Log A = .994 + 1.058 log a. 

 In the calculation, 2A is used because Turrell 's formula just 

 measures the dorsal surface area. Using this set of formulas and the 

 calculated averages wherever possible, the author arrived at some es- 

 timated number of snails needed per tree (Table 10). 



The author estimated that because of the short, four month acti- 

 vity period of the snails, that a T value of 15 to 30 days should be 

 used. This means that the entire leaf surface of the tree should be 

 cleaned within this period. Several factors such as ambulatory move- 

 ment, and original snail distribution on the tree may tend to make the 

 T period longer than calculated. For this reason the snail values N 

 for 15 days were calculated. 



The trees, evaluated in Chapter II, Section 1, dealing with snail 

 population per tree, were 25 year old trees. Reference to Table 10 

 shows that up to 168 snails per tree would be needed to clean totally 

 the tree surface in a 15 day period. Even if the lower value of 

 84 snails for 30 days is used, it is quickly realized that the 1976 

 populations were too low to afford the control needed. An average of 

 only 45 snails per tree were found. At this rate the earliest the 



