TREATING HOLLOW TREES. 187 



of France, the great heat of summer renders coal tar so liquid that 

 it is impossible to properly treat wounds made at that season. 

 In such cases another coat should be applied during the following 

 winter.* 



^Removing Shoots and Suckers. — Many street trees, espe- 

 cially elms, which have suiFered from the effects of bad 

 pruning, send forth shoots or suckers from many points of 

 the trunk. These shoots are believed to be detrimental 

 rather than beneficial to the tree, impairing the development 

 of its top and larger branches. So long as suckers are 

 allowed to remain, many of the gypsy-moth caterpillars 

 will seek shelter among them during the day in preference 

 to going to the burlap. If suckers are carefully removed, 

 no injury to the tree will result. 



Treating Holloiv Trees, — When the trunks and larger limbs 

 of trees are riddled with holes caused by neglect or bad 

 pruning, another mode of treatment becomes necessary. 

 Thousands of gypsy caterpillars which feed upon the foliage 

 at night will retire through the holes to the interior of 

 the hollow trunks and branches, where they secrete them- 

 selves during the day, emerging at night to continue their 

 destructive work under cover of the darkness. The clos- 

 ing of such cavities by filling, covering or sealing them is 

 an important auxiliary to the other means of extermination. 

 It prevents the caterpillars from hiding and the moths 

 from ovipositing within the hollow trunks and branches, 

 and drives them to the burlap for shelter. If the holes 

 are carefully covered in the winter, many eggs are en- 

 closed within. When they hatch in the spring, the young 

 caterpillars are prevented from leaving their hiding-places 

 and are thus buried alive, as it were, in the tree trunks. This 

 work must be very thoroughly done to prevent the escape 

 of the minute, newly hatched caterpillars. 



During the work of the first gypsy moth commission 

 many holes were filled with hydraulic cement. If the hole 

 was large, it was packed with stones and a coating of cement 

 put on the face of this filling at the mouth of the hole. If 

 the hole treated was in a large and otherwise sound trunk. 



* " Tree Pruning," by A. Des Cars, pages 58 and 59. 



