A NEW SUMMER SPRAY 
FOR OYSTER-SHELL SCALE 
C. L. BURKHOLDER 
Purdue University 
Protecting Your Lilacs, Dogwoods, and a Score 
of Other Favorite Ornamentals from this Persist¬ 
ent Pest Commonly Seen Both North and South 
H E most wide-spread and oftenest seen of the scale in- 
sects infesting shade trees and ornamental shrubbery 
is the oyster-shell. It is readily distinguished from all 
other scale insects infesting deciduous trees by its gray¬ 
ish brown color and peculiar shape, resembling a miniature 
oyster shell. The female scale is about an eighth of an inch 
long and tapers to a decided point at one end. The male 
scale is much smaller, of a lighter color, and thread-like 
in shape; they are seldom found in the areas infested bv 
the female and are of little importance as far as direct in¬ 
jury to the tree or shrub is concerned. 
During the later part of the sum¬ 
mer the female scale deposits from 
30 to 100 minute, white eggs un¬ 
der the broad end of scale covering. 
The body of the female shrivels up 
into a small area in the tip of the 
scale covering and dies in the late 
fall. The eggs remain under the old 
scale till the following spring and be¬ 
gin to hatch from the seventh to twenty- 
first of June, in the latitude of Colum¬ 
bus, Ohio. The hatching period is 
retarded or advanced north or south 
of this point, about one day for each 
fifteen miles. Local weather conditions 
will vary the hatching date several 
weeks. The young scale are pale 
yellow in color and very active. They 
can be seen easily with the naked eye 
as they scurry around looking for 
a suitable spot for their permanent 
home. 
T HERE is a single generation of 
oyster-shell scale each summer in 
the North, but in the latitude of 
southern Pennsylvania and far¬ 
ther south there are two genera¬ 
tions, the second hatching in August 
or September. 
The fact that the scale passes the 
winter in the egg stage makes it a 
difficult insect to control. The ordin¬ 
ary insecticides used during the dorm¬ 
ant season for scale insects, such as 
San Jose scale, kill only a small 
percentage of the eggs of the oyster- 
shell scale. This is because the eggs 
are so well protected by the so-called 
armor or covering that it is almost impossible to get the 
spray in direct contact with the eggs. In the North a daily 
inspection must be made for hatching scale beginning 
about June 1st. In the South it is often necessary to watch for 
the second generation in August and spray again as soon as the 
young “ crawlers ” are discovered. 
S UMMER spraying just at the time the eggs are hatching has 
been practised, using kerosene emulsion, but this material 
sometimes injures the foliage of both the shrubs and trees, and 
is generally unsatisfactory because kero¬ 
sene emulsion is difficult to prepare 
properly. Recently a much better 
summer spray has come into use. It 
is made up as follows: dissolve one 
pound of whale oil, or fish oil soap 
by heating in a small quantity of 
water; stir this into five gallons of 
water to which has been added 1 oz. 
of Black Leaf 40 tobacco extract. 
Ordinary laundry soap is sometimes 
used in place of the fish oil soap, but 
is not as effective. 
Successful control depends on ap¬ 
plying the spray just after the insects 
hatch and while they are still in the 
crawling stage. They very soon settle 
down, insert their long thread-like suck¬ 
ing beaks into the bark of the tree and 
commense to secrete a roof over their 
backs. The females never move from 
this spot and the cover is soon suffici¬ 
ently thick to protect the body of the 
scale beneath from injury by a spray 
material. 
Lilacs and Dogwoods are particu¬ 
larly susceptible to oyster-shell scale. 
All varieties of Ash and Poplar trees 
are especially attractive to this insect 
and are frequently entirely killed by 
them. Over twenty-five varieties of 
ornamental trees are known to be hosts 
to this pest. Many fine old shrubs and 
trees are killed or injured by this insect 
every year. This loss could be entirely 
prevented by a timely application of 
the tobacco-fish-oil spray. Examine 
the ornamental plantings about your 
grounds and plan to destroy this pest 
before it is too late. 
A female oyster-shell scale from 
beneath, filled with over-wintering 
eggs. The dead, shriveled female 
appears at one end. Spraying at 
this stage is not effective and control 
measures should be employed very 
soon after the eggs hatch. (Actual 
size about one-eigth of an inch) 
ATTACKING THE LILAC 
A typical manifestation of oyster-shell scale on a 
branch of L.ilac. This shrub will be killed before the 
end of the summer unless given timely spraying 
333 
