April, ’20] 
GLENN: OYSTER-SHELL SCALE 
177 
shell scale, we may infer that this is also true in other states. It is 
much more destructive than the other forms and observations made 
during the last six years lead us to believe that it will eliminate the 
poplar and the ash and possibly all of its favorite host plants from 
parks and lawns, unless systematic control measures are adopted, 
or some parasite or other nautral enemy appears to keep it under 
control. The only evidence of such an enemy which has come to our 
attention was the receipt some time ago from the northern part of 
Illinois of some lilac which had been heavily infested by the scale, 95 
per cent of wdiich had been destroyed evidently by a bird or some 
predacious enemy. 
This insect can be controlled by spraying with the lime sulphur 
wash, but the spraying of large shade trees is expensive and requires 
apparatus built especially for this kind of work. Spraying large street 
trees and trees in lawns is in many cases impracticable, because it is 
impossible to spray them with the lime sulphur wash without ruining 
the paint on nearby buildings and this wash is by far the most effective 
dormant spray for this insect. Miscible oils have not proven satis¬ 
factory. The only practicable method of procedure is to cut down 
infested trees which cannot be sprayed and replace them with others not 
susceptible to this pest. Poplars are especially objectionable because 
the scale multiplies so rapidly on them. Because of their tall growing 
habit they are exceedingly difficult to spray, and because of their hardi¬ 
ness they resist the attack of the scale and serve as disseminating 
centers for it for many years. For these as well as for other good 
reasons the poplar should be eliminated from city plantings, and other 
trees, not susceptible to the scale substituted. A very careful inspec¬ 
tion should be made of nurseries and all infested stock destroyed at 
once. Since the control of this pest is for the most part a city problem, 
the attention of city authorities should be called to it, and drastic 
measures recommended, if necessary. 
Mr. Childs: I might say that in Hood River, Oregon, there oc¬ 
curs conditions relative to the habits of the oyster shell scale of much 
the same nature as Mr. Glenn speaks. We often find dogwood being 
killed by the scale in ravines running through orchards and no scales 
will be found on the apple trees adjoining. I have also noted this 
difference in the texture of the scale on different host plants. 
Mr. J. S. Houser: I was interested in what Mr. Glenn said as to 
the probable injury to ash by this scale. Several years ago, about 
fifteen, we had a very severe attack of this scale on ash in Northern 
Ohio. The attack was virulent for a number of years, and then it 
disappeared almost entirely. It required a period of something like 
