300 JOURNAL OF' FORESTRY 



The curve* shown in figure 4 illustrates this point. This curve 

 was constructed from counts on sample plots made near Grande, in 

 northern Isanti County, Minnesota. Up to a density of 400 trees per 

 acre, 100 per cent are infested. Above that point the percentage in- 

 fested constantly diminishes until at 4,500 per acre the infestation is 

 slightly less than 10 per cent, while at 9,000 trees per acre the infesta- 

 tion is reduced to less than i per cent. One plot, where the trees stood 

 11,200 to the acre, only 0.5 per cent were infested. This plot was 

 within 100 feet of another more open plot of the same age which had 

 an infestation of over 50 per cent. 



With this decrease in weevil attack the density increases, and with 

 a larger number of trees per acre there is a corresponding reduction 

 in the average loss per tree in height growth as shown in figure 5. This 

 curve was constructed on the basis of six-inch loss in height growth for 

 each weevil attack, which is a very conservative figure. 



Density also has a direct bearing on the per cent of unmerchantable 

 material resulting from weevil injury, as is illustrated by the curve in 

 figure 6. This is due partly to the increased stimulus to height growth 

 resulting from competition in the denser stands, which hastens recovery 

 from weevil injury, and partly the crowding out of deformed and 

 crippled trees by the healthy and vigorous individuals. 



Control Measures 



Several very good methods for the control of the white-pine weevil 

 in ornamental or other small plantings have been suggested, such as 

 spraying, collecting adults in the early spring, pruning out and burning 

 infested shoots during June and July, and others equally impracticable 

 under ordinary forest conditions. The most feasible of the above 

 recommendations, that of pruning and burning weeviled shoots, can- 

 not be done for less than $1.50 per acre each year and would neces- 

 sarily have to be carried over a period of from five to ten years in 

 order to accomplish good results. Unless regular employees can be 

 used for this work during slack seasons, the cost is prohibitive. 



From the results of this study, the most economical and eiifective 

 method for controlling the weevil is by close planting. Under present 

 Minnesota conditions the standard density of 1,210 trees per acre is 

 dense enough to insure a final crop with few or no unmerchantable 

 trees, although there will likely be a number with bad crooks or forks. 



* The number of trees per acre, as shown in this and other curves in this article, 

 represents the original number of trees before any were crowded out, and the 

 weevil injury in each case represents the condition at the time the stand is 30 

 years old. 



