6 N. J. Agricultural Experiment Stations Circular 156 



layer of tissue. Dead tissue is usually dry and tight against the hard wood. 



Para-dichlorobenzene is called or is obtainable in the market under the 

 names para-dichlorobenzene, para-dichlorobenzol, "Paracide," "Krystal 

 Gas," "P.D.B.," paradichlor, etc. 



Para-dichlorobenzene seems to be a difficult word to remember and pro- 

 nounce, consequently the author suggests the abbreviation "p-c-benzene." 

 Some companies are placing on the market compounds for the control of 

 the peach-tree borer which contain a small or large percentage of para- 

 dichlorobenzene plus a small or large amount of inert substances. Since 

 pure para-dichlorobenzene is the only chemical known which has proved 

 to be satisfactory in the control of the peach tree borer, the author sees no 

 reason for making use of, or paying for compounds containing substances 

 other than para-dichlorobenzene when one can obtain pure crystalline 

 para-dichlorobenzene. If a compound contains 25 per cent para-dichloro- 

 benzene, it will be necessary to use four times as much of the compound 

 as of the pure para-dichlorobenzene to obtain a satisfactory dose. In case 

 a compound containing substances other than para-dichlorobenzene is used, 

 the para-dichlorobenzene content of the product should be ascertained be- 

 fore it is employed. The price of pure para-dichlorobenzene ranges from 

 $.20 to $1.00 per pound. In 100-pound lots peach growers in New Jersey 

 have obtained pure para-dichlorobenzene for 20 to 30 cents per pound. 

 Trees 6 years of age or older may be treated (including the labor cost) for 

 2 to 4 cents per tree. 



Age of Trees — Short Treatments 



Our experiments and observations to date warrant us to recommend 

 the use of para-dichlorobenzene on infested peach trees (in the orchard) 

 of all varieties which are 3 years of age or older. For trees 6 years of 

 age or older the para-dichlorobenzene may be permitted to evaporate with- 

 out removal, while on trees 3 to 5 years of age we advocate the removal 

 of the crystals as soon as the larvae are dead. The length of time required 

 to kill the borers depends upon soil temperature, size of the larvae and to 

 some extent upon the moisture content of the soil. Under most conditions 

 when the soil temperature 3 to 6 inches deep averages 55° to 70°, 3 weeks' 

 exposure will kill the maximum number of the larvae (90 to 100 per cent) . 

 Average soil temperatures between 55° and 70° F. at a depth of 3 to 6 

 inches occur during May, early in June, September and early in October 

 in New Jersey. During most of June and in July and August the average 

 soil temperature is 70° F., or higher. High soil temperature brings about a 

 rapid evaporation of para-dichlorobenzene crystals and trees subjected to a 

 great concentration or distribution of the gas are apt to show the maximum 

 amount of injury. To kill large larvae a longer exposure to a given amount 

 of gas is required than with small larvae. Unless the soil is exceedingly 

 wet, so that all of the pores are filled with water, the moisture content of 

 the soil will not interfere with the results in a 3 weeks' exposure. Soil 

 texture appears to have little or no influence on the results. 



When employing a short treatment on trees 3 to 5 years of age the para- 

 dichlorobenzene is applied in the manner described. After 3 weeks when 

 the larvae are dead, the dirt of the mound and unevaporated crystals are 



