32 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



dant humus and feed on the roots of various plants. They are most 

 injurious early in the spring. At the State nursery at Corvallis, 

 Oreg., hardwood seedlings have been damaged, but conifers are 

 not seriously affected (124). Soil fumigation with D-D mixture 

 or with ethylene dibromide before planting has proved effective 

 under experimental conditions. 



APHIDS 



Aphids (see p. 56) are often found in clusters on the tender, 

 growing tips of nursery stock. Usually they are not abundant 

 enough to cause appreciable injury, but, if they are, they can be 

 easily controlled with a miscible oil or nicotine sulfate spray. 



INSECTS INJURIOUS TO YOUNG TREES 



(SEEDLINGS, SAPLINGS, AND POLES) 



Trees in plantations and forests are subject to attack by a 

 great many insect pests while they are growing from seedlings to 

 maturity. At first they may be attacked by root-feeding insects. 

 Later another group of insects feed on the rapidly growing ter- 

 minal shoots, laterals, tips, or buds. This type of damage seldom 

 kills the young trees, but it often seriously deforms or stunts them. 

 As buds and terminals are killed, the tree throws out new buds 

 and shoots, which results in much branching. The tree becomes 

 bushy, with the main trunk crooked and gnarled, and is often 

 permanently ruined for commercial use. At this stage of the tree's 

 life, leaf-eating and bark-feeding insects also begin to be im- 

 portant. 



The control of insects affecting young trees rarely calls for 

 direct control measures. A certain amount of insect damage is 

 normal in natural forests and is only a part of the natural thin- 

 ning process. When an epidemic develops as the result of some 

 disturbance of the natural balance, as through the creation of an 

 abundance of slash, windfall, or fire-injured trees, some direct 

 control action may be necessary to protect the younger trees. 

 Usually the indicated remedy is avoidance of the conditions that 

 induce epidemics or the prompt disposal of breeding material. In 

 plantations, or on trees of special value, some attention to insects 

 may be justified. 



Key to Diagnosis of Insect Injury to Young Trees 



A. Entire tree, or large part, sickly, dying, or dead; foliage fading, 

 turning yellow or red. 



1. Tunnels or borings found under the bark of the main 



trunk or larger branches Cajnbium feeders, p. 126 



2. Foliage fed upon, partially or wholly stripped from the 



trees or appearing sparse and sickly Defoliators, p. 75 



3. Insects found feeding on the roots. 



a. Bark gnawed by large black ants and dark, soft- 



bodied aphids sucking sap from wounds 



Carpenter ants and root aphids, p. 34 



b. Tunnels or borings under bark of larger roots 



Root bark beetles, p. 35 



