226 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



Figure 105. — Trimotor spray plane in action on the 1947 tussock moth 

 control project in Idaho. 



beetle-control project may last for years or they may be of 

 extremely short duration. 



In justifying the application of measures for the control of bark 

 beetles, such factors as the value and merchantability of the 

 timber, the destruction of the forest cover in its relation to 

 watershed protection, the creation of fire hazards, and the danger 

 of the epidemic spreading into more valuable stands of timber 

 must be considered. The proper evaluation of these factors, bal- 

 anced against the cost of the operation, will determine the 

 economic justification of the project. However, it is difficult to 

 foresee the extent of the probable damage or the course the 

 epidemic may take if no control is undertaken, and conclusions 

 as to the success of a bark-beetle project can only be deduced 

 on the basis of an estimate of what would have happened had 

 no control work been undertaken. Control measures applied 

 during the decline of an outbreak often tend to place an inflated 

 value on the results obtained. On the other hand, control under- 

 taken during the time an outbreak is building to an epidemic 

 may show little reduction in damage and give the appearance of 

 failure. The best that can be done is to compare the trend of the 

 epidemic on the treated area subsequent to control with that 

 on a similar neighboring area where no work was done. 



