368 



ARBORICULTURE 



ARBORICULTURE 



their eggs on the bark of the trees. The eggs soon hatch 

 into larvae which feed for a time and then over-winter 

 in a small cell beneath the bark. Next year they bore 

 through the living wood and transform in August to 

 beetles. This species can destroy 

 healthy locust trees rapidly and is 

 a very serious pest wherever the 

 tree is grown. All infested trees 

 should be pruned or felled and 

 burned to destroy the larvae, in 

 the fall or winter. Sugar maples 

 suffer from a similar insect, as do 

 practically all sorts of trees. 



White pine trees are commonly 

 deformed by the larvae of the 

 white-pine weevil which feed ex- 

 clusively beneath the bark of the 

 terminal shoots of young trees of 

 this species. (Fig. 344.) 



The carpenter moth, Prionoxys- 

 tus robinix, is a large common 

 mottled gray insect with pale 

 yellow black-headed and black- 

 speckled larvae 2 inches in length, 

 that bore in the branches of many 

 kinds of trees. Oak suffers most, but maple, ash, locust, 

 willow and cotton wood are often infested. The moth 

 lays its eggs on the bark late in the summer, and for 

 two or three seasons the larvss feed on the wood, cut- 

 ting large circular burrows. They transform in the 

 burrow, the pupa working its way partly through the 

 bark for the eclosion of the moth. The brown pupa- 

 case may then remain projecting from the mouth of 

 the burrow for some time. A related European insect, 

 the leopard moth, Zeuzera pyrina, has recently become 

 abundant along the northern Atlantic coast region, 

 attacking elm and all sorts of other trees and shrubs. 

 It feeds in the same way and bids fair to become 

 one of our worst shade-tree pests. The larvae of 

 many other moths injure trees in a more or less 

 similar way. 



The pigeon horn-tail is a large cylindrical yellow- 

 brown and black insect with grub-like larvae that bore 



344. Injury to tip of 

 white pine sapling by 

 white-pine weevil. ( Xi) 



345. Phylloxera galls on chestnut. ( X H) 



in elm, maple, and other trees. The females insert 

 their eggs deep into the tree by means of a needle-like 

 ovipositor. They frequently fail to extricate the ovi- 

 positor and may be seen dead, but still attached to the 

 tree trunks. 



E. Leaf-miners. 



Small larvae belonging to several orders of insects 

 live as miners in leaves, the most abundant forms often 

 greatly disfiguring the foliage of affected trees. 



Deciduous trees of all sorts are affected by the leaf- 

 mining larva; of various small moths, but it is very diffi- 

 cult to distinguish the different species without minute 

 study. Oaks are particularly susceptible and are com- 

 monly disfigured by the sinuous or irregularly rounded 

 mines that appear as pale streaks or blotches. Even 

 pines suffer from such larvae, which enter a needle and 

 eat out the tissue, causing the tip to dry and become 

 yellow. Occasionally insect larvae cause malformations 



or swellings of the leaves or twigs, known as galls. 

 (Figs. 345, 346.) 



Yellow locust suffers from a leaf-mining beetle larva, 

 Odontota dorsalis, that eats out almost all of the leaf 

 parenchyma, causing the leaves to dry and shrivel. 

 Related species affect oak and basswood. Members of 

 another family, belonging to the genus Brachys, also 

 mine in leaves of oak, chestnut, and so forth. 



One leaf-mining saw-fly is of considerable importance, 

 Kaliofenusa ulmi, the larva; of which eat out the paren- 

 chyma of elm leaves between the lateral veins, causing 

 them to assume a seared appearance in spots (Fig. 

 347). Another closely related species mines in the 

 leaves of the hawthorn (Cratffigus). The latter may 

 be satisfactorily killed by a spray of tobacco-water, 

 but the species on elm is more 

 resistant. The larvae of these 

 species enter the ground later in 

 the summer to spin their cocoons. 

 C. T. BRUES. 



346. Mite-galls on maple. ( X H) 



347. Leaf-miners' galler- 

 ies in elm. 



Some types of tree diseases. 



Disease in plants is the result of any derangement in 

 the normal form, structure or physiology of the organ- 

 ism. The disease condition becomes manifest by differ- 

 ent symptoms, according to the nature of the disorder. 

 Such symptoms as stag-head, cankers, leaf-spots, 

 witches' brooms, and so on, are examples of the effect 

 produced in the tree by some disease-producing agent or 

 combination of agents. The variety of functional dis- 

 orders alone that may arise in trees is large. Such 

 causes as insufficient or excessive soil water, mal- 

 nutrition, excessive heat or cold, or rapid variations 

 in temperature are capable of producing effects called 

 physiological diseases. On the other hand are those 

 diseases that are produced by the activities of para- 

 sites, such as certain of the fungi, and bacteria. Accu- 

 rately to place a new or little-known disease in one of these 

 two classes is often difficult for the expert, even after 

 much study. There is relatively less known concerning 

 the physiological diseases of trees than of those caused 

 by parasites, not because of their less importance so 

 much as of the difficulty of studying them. It is to be 

 deplored that the diseases of forest, shade and ornamen- 

 tal trees have not received their due share of study and 

 investigation by pathologists. 



How fungi cause diseases of trees. 



The fungi consist of a group of plants that do not 

 contain chlorophyll, upon which all green plants depend 

 for the synthesis of carbohydrates. Consequently, not 

 being able to manufacture their own food, the fungi 

 must secure it from their environment, by dissolving 

 and utilizing organic materials from dead or living 

 plant or animal bodies. By far the vast majority, 

 luckily, belong to the class of scavengers which attack 

 dead organic material and utilize it for food. These 

 forms are cajled saprophytes. Other species of the 

 fungi attack living plants and, through their activities, 

 produce the disorders that are termed diseases. These 

 are known as parasites or pathogens. 



