Tree Diseases. 



19 



trees after the middle of July. The adults feed upon the tender 

 parts of the leaf during early summer, while the larvae feed upon the 

 under surface of the leaves, eating away the more delicate portions 

 between the larger veins and taking out the green portions between the 

 epidermal layers. This causes the rusty appearance of the trees, very 

 much as though they were dying ; many of the leaves in fact, do fall. 

 Since the foliage is not usually attacked by the larvae until the middle 

 of July, when the trees have made their principal growth, the insects 

 have not so far caused a great amount of damage. The trees leaf out 

 again next spring as usual, and aside from retarding the growth in the 

 latter part of the season, and the disfigured appearance of the trees, 

 no serious consequence is the result. The disease was apparently much 

 more pronounced in 1913 and 1914 than was the case in 1915, and 

 scarcely noticeable in 1916, indicating that it passes through certain 

 cycles, in common with most insect pests. There appears to be no prac- 

 tical remedy for dealing with the disease under forest conditions, al- 

 though in the ease of shade trees spraying early in the season, to 

 poison the leaf-eating adults, is beneficial. Since the larvae feed be- 

 tween the epidermal layers of the leaf and cannot be reached by a 

 spray, it seems impracticable to attack them at that stage. 



The Two-Lined Chestnut Borer, Agrilus hilineatus, is believed to 

 have caused considerable damage to chestnut in southern Maryland, 

 and also to be responsible for killing many oak trees. The insect 

 operates just under the bark of the tree, making galleries from six to 

 ten inches long, which run more or less horizontally around it. When 

 the tree is attacked by a number of these insects it is quickly girdled. 

 The name of this borer is derived from the appearance of the adult 

 beetle, which appears during May and early June. It is about three- 

 eighths of an inch long, black in color, and marked with two yellowish 

 lines extending longitudinally along the back. It has one or more 

 parasites which apparently are holding it in check, so that the amount 

 of damage done has not been considerable as yet. 



Fungous Diseases. 



Among the fungous tree diseases of the State the only one of far- 

 reaching importance is the Chestnut Blight — Diaporthe parasitica. 

 It is not known for how many years this disease has been present in 

 Maryland, but it was observed in 1910 as a particularly virulent dis- 

 ease that was spreading rapidly in the northeastern part of the State. 



This parasitic growth was probably introduced from China, and 

 has spread more rapidly and caused more damage than any other 

 tree disease in the country. It affects only the chestnut and chinqua- 

 pin, attacking trees of all sizes, and while the attack is usually in the 



