10 Wyoming Experiment Station. 



the tree "bleeds" injuriously. Besides, such bleeding wounds 

 are always points of attack by insects and germs. Fall and win- 

 ter pruning is all right except that it leaves the wounds for a 

 longer time unprotected by new growth and increases the loss 

 of water by evaporation during the winter months. 



INSECTS. 



Shade trees are not exempt from insect pests and fungous 

 diseases. Very few people are, however, .willing to .take the 

 trouble to spray regularly, that these may be kept in check. 

 Often it would be a matter of real economy to do so, but per- 

 haps the best we can hope for, with the present interest in 

 shade trees, is some care in the selection of species. Some are 

 less subject to insects than others, and there is also a decided 

 difference in the resistence to the attacks of fungi. 



The cottonwoods are reasonably free from fungi, but the 

 narrow leaved form is peculiarly susceptible to the attacks of 

 the small green plant lice. The broad leaved and the lance 

 leaved ("smooth-bark") species are. fairly free from lice, but 

 their leaves are in recent years greatly infested with the leaf- 

 miner. Since all three of these are very important trees, in the 

 higher altitudes of the state especially, we ought to take some 

 precautions against these enemies. 



Plant lice may be kept in check by spraying, and it is 

 quite well , established that their ravages may also be greatly 

 checked by ridding the immediate vicinity of the trees of all 

 ant nests. Ants feed upon the sweet exudation from the bodies 

 of the lice, and because of this very personal interest in them 

 the ants take great care not only in the preservation and dis- 

 tribution of the lice during the growing season, but great in- 

 genuity is displayed in the wintering of their "cows," as the 

 plant lice are often called. Destroy the ants. This may be 

 done by scalding with hot water, or by the carbon bisulphide 

 treatment.* 



*For methods see Bulletin 38. of this Station, in which will also he found directions for the 

 destruction of other insect pests. 



