P-C-Benzene for the Peach-Tree Borer 5 



found. The author has repeatedly had the experience of returning to trees 

 which have been carefully "wormed" and examined two, three and in some 

 cases four times, and finding a few larvae if a large number of trees are 

 examined. It is almost impossible to remove all of the larvae in a heavily 

 infested tree by "worming" and at the same time produce little or no injury 

 by cutting. If it is necessary to cut the tree severely to reach a larva the 

 operation will be as detrimental to the tree as the injury the larva may 

 produce. 



When the "worming" process is complete replace the soil as soon as pos- 

 sible and mound it up around the tree about one foot. The presence of a 

 mound about the tree during the summer is desirable if the "worming" 

 process for the control of the borer is practised. The mound about the 

 tree causes most of the larvae to enter the tree above the general level of 

 the ground and this makes it easier to "worm" the trees. If para-dichloro- 

 benezene is employed as a control measure no mounds of dirt should exist 

 about the tree during the summer because the most successful results are 

 obtained with the gas treatment when the majority of the larvae are in the 

 tree at or just below the general level of the soil. The presence of a mound 

 about the tree during the winter protects the trunk from frost injury. 



Para-dichlorobenzene 



(P-C-Benzene) 



Chemically pure para-dichlorobenzene (C 6 H 4 C1 2 ) is a white crystalline 

 solid that is insoluble in water and vaporizes slowly at ordinary tempera- 

 tures. Crystals of para-dichlorobenzene small enough to pass through a 

 sieve with 10 meshes to the linear inch are most desirable. Large solid lumps 

 are not satisfactory. The crystals should be dry. If wet or partly sub- 

 merged in a liquid the substance is not chemically pure. The liquid or wet 

 condition indicates the presence of highly toxic (for plants) chlorinated 

 benzene products. The vapor of para-dichlorobenzene is heavier than air. 

 One-ounce treatments placed about peach trees when the soil temperature is 

 70* F. or higher requires about six weeks or longer for complete evapora- 

 tion, while similar treatments made late in the fall (November) when the 

 soil temperature is 50° F. or lower will remain about the trees until late 

 in the spring or early summer of the following year. 



So far as is known para-dichlorobenzene is non-poisonous to man and 

 poultry, but it is decidedly poisonous to most insects when they are exposed 

 to the fumes for a considerable period of time. The gas is also injurious to 

 tender roots and the growing tissue of most plants. Fortunately the bark 

 on peach trees, particularly on trees three years of age or older, appears to 

 act as a barrier and protects the growing tissue about the cambium layer 

 when para-dichlorobenzene is applied. Most, peach trees treated with para- 

 dichlorobenzene will show some discoloration, a dark or reddish brown 

 color, in the outer bark. This abnormality appears to be of no importance. 

 When more severe injury occurs the light-colored tissues near the cambium 

 layer contain numerous small brown specks. If the injury is serious the 

 specks become enlarged and join together forming a continuous brown dead 



