85 



THE COTTONY MAPLE SCALE: AN UNUSUAL OUTBREAK, AND 

 EXPERIMENTS WITH INSECTICIDES. 



By S. Arthur Johnson, Fort CoUiiu, Colo. 



Contrary to general experience the cottony maple scale (Pulvinaria 

 inninneixiMlis Rath v.) has done serious injury in Denver for several 

 years past and gives promise of renewed ravages during the coming 

 summer. The scale is widely distributed over the city on the soft 

 liiaple {Acer saccJiariniDn) shade trees in the paries and streets. In 

 a number of localities the permanent injury has been severe. Two 

 winters ago the time of one man was employed for two weeks cutting 

 out and removing the dead limbs from a park covering one block. 

 In this same park last winter the under surfaces of many limbs on the 

 soft maples and black locusts {Rohiiua p^eudacafrhi) were literally 

 coated with the scale. Here the Colorado Agricultural College, in 

 conjunction witli the superintendent of parks, conducted a number of 

 experiments for the pm-jjose of discovering an ell'cctiv^e winter treat- 

 ment. So far as the writer is aw^are very little tliorough work has 

 been done in this line. 



The advantages of a winter treatment are indicated both by the 

 condition of the trees and by the life history of the insect. The im- 

 mense numbers of the pest would make it necessary to spray thor- 

 oughly both surfaces of the leaves in summer, Avhich is a prac- 

 tical impossibility Avith trees of dense foliage which are often 30 

 or more feet in height. Moreover, it would seem that the life 

 history of the insect would necessitate more than one application of 

 the spray. Doctor Howard,*^ in giving the life history, says: 



TbG young hatch early in sniumer. usually in the month of June, but occasion- 

 ally at least as early as May 22. The hatching period usually extends on into 

 early July, but may last until August. * * * jj^ ^jjg course of a month they 

 undergo a molt and begin to secrete a certain amount of wax from the dorsal 

 surface of the body. 



It thus appears quite possible that some of the first-hatched insects 

 may molt and become protected with scales before the last of the 

 eggs have hatched. Professor Gillette ^- has expressed the opinion that 

 after the wax is formed sprays of greater strength will be necessary. 

 The leaves of the soft maple appear to be quite sensitive to the greater 

 strengths of contact insecticides. 



EXPERIMENTS WITH INSECTICIDES. 



Shortly after I came to this station a quantity of badly infested 

 maple twigs were received from Colorado Springs. At that time, 

 under the direction of Professor Gillette, I made a number of experi- 



a Bui. 22. n. s., Div. of Ent., U. S. Dept. Agric, pp. 7-16. 

 6 Bui. 47, Colo. Exp. Sta., p. 33. 



