ORCHARD INSECTS OF THE PACIFIC NORTHWEST 



55 



to place paradichlorobenzene ("PDB") about the tree trunks in the 

 fall. This chemical is in the form of white crystals having a charac- 

 teristic odor a little like that of naphthalene, and forming a gas that 

 is heavier than air. When properly used, paradichlorobenzene kills 

 practically all of the borers without injuring the trees, and is not 

 harmful to man or animals. 



After the ground has been leveled off, the paradichlorobenzene 

 should be placed about the tree trunk in a ring about V/ 2 inches from 

 the trunk and 1 or 2 

 inches wide (fig. 62), 

 using from % to 1 

 ounce of the crystals 

 to each tree, depend- 

 ing on its size. Care 

 should be taken not to 

 place the crystals in 

 contact with the tree 

 trunk as they may in- 

 jure the tree, and not 

 to make the ring more 

 than 2 inches from the 

 trunk, as it would not 

 be so effective at a 

 greater distance. The 

 ring of paradichloro- 

 benzene should be cov- 

 ered with several 

 shovelfuls of earth, 

 which should be packed 

 down with the back of 

 the shovel. The para- 

 dichlorobenzene should 

 be applied between 

 August 15 and Sep- 

 tember 15. At this 

 time the borers are 

 small and easily killed. 

 Later, cold weather 

 may hinder the forma- 

 tion of gas from the 

 crystals, as this pro- 

 cess requires a soil 

 temperature of at least 60° F. To prevent any possible injury to 

 the trees from the gas, the remaining crystals of paradichlorobenzene 

 should be scattered away from the tree with a shovel a month or 6 

 weeks after they are applied. If paradichlorobenzene is to be kept 

 for a time, it should be stored in airtight containers to prevent loss by 

 evaporation. 



During the past few years a new material has been found of value in 

 peach borer control. This is an emulsion of ethylene dichloride ap- 

 plied to the soil around the base of the tree. This material has the 

 advantage of being more effective than paradichlorobenzene at low 

 temperatures and of being less likely to cause injury to young trees. 



Figure 62. — Correct method of placing paradichloro- 

 benzene for controlling the peach borer. 



