MICHIGAN EXPERIMENT STATION BULLETINS 331 



INSECTS AND DISEASES AND TTIKTII TREATMENT. 



The followiuy brief deseiipliuiis of some of the more daii<;ei'ous insects 

 and diseases of fruit trees are given with the hope that they may aid in 

 the detection of the presence of these pests and secure their prompt treat- 

 ment. Especial attention is jiiven to tliose that come under the oi)eration 

 "of the orchard and nursery hiws of ]Michiy,an, in order lliat the persons 

 selected as commissioners in the different townships may have some 

 guide that will aid them in recognizing the nature of the trouble, and In 

 determining the pro])er treatment or remedy. As the remedies often fail 

 from the fact that the nature of the insect or disease is not understood, 

 it is urged that when any doubt exists specimens be mailed to State 

 Experiment Station, Agricultural College, Mich. They will be examined 

 and reuKHlies given if possible. 



SAN JOSE SCALE. 



This most dangerous of all our fruit-tree pests has been found in a dozen 

 or more places in the state and undoubtedly exists in still others. Every 

 effort should be made to destroy the colonies we now have and to prevent 

 its introduction to uninfected sections. 



The insect has little power of locomotion, but may be brought in upon 

 nursery stock, or can be carried by birds, and ants and other insects, 

 from tree to tree. It attacks all of our fruit plants and has been found 

 upon various kinds of forest trees. 



It propagates very rapidly and three or four broods may develop in a 

 season, so that it will quickly incrust the branches of a tree, which will 

 then look as if plastered with coal ashes. When they first appear, they 

 have a louse-like form and can move about, but they soon settle down, 

 insert their slender beaks into the bark and develop scale-like coverings. 

 During the winter the partially developed scales are black in color, nearly 

 round, flattened; and in most cases, as can be seen with a magnifying 

 glass, have a small nipple at the center, surrounded by a well-marked 

 sunken ring. The size is such that a single scale to the unaided eye looks 

 like a small black spot. The full-grown scales are of a grayish-brown 

 and reach one sixteenth of an inch in diameter. The scales are but loosely 

 attached to the tree and can be readily scraped off. Beneath the shell- 

 like covering the true insect can be found. These are yellow in color and 

 on being crushed will be found to contain a yellow oily substance. 



When the scales are scattered upon the young twigs a purplish color of 

 the bark will be noticed and on cutting into the bark it will be found 

 much discolored. This discoloration of the inner bark is caused by no 

 other scale, and if this is present and the ring-like depression can be made 

 out, it indicates that it is the San Jos^ scale. This insect will ruin, if it 

 does not kill young fruit trees, and will render large trees unfruitful, and 

 is to be dreaded ])articularly on account of its rapid reproduction and 

 small size, which render it possible for it to obtain a foothold, and even 

 spread to adjoining trees before it is discovered, as well as because it is 

 difficult to leach and destroy every specimen upon a tree with a spraying 

 solution, while the cost of the materials will nuike it an expensive under- 

 taking. 



