1 ounce of mercuric cyanide in 4 gallons of 
water. Both of these chemicals can be obtained 
at drugstores. Corrosive sublimate is sold in 
tablet form with directions for making up a 
1-to-1,000 solution. These chemicals are deadly 
poisons and should be treated as such. Since 
these solutions will corrode metals they should 
be kept in glass or wooden containers, and all 
tools should be carefully cleaned after use. 
Removing blighted blossoms and twigs as 
they appear in the spring is usually impracti- 
cable, except when only a few trees are affected. 
Even then, unless great care is taken to cut well 
below the infected areas and to sterilize the 
tools between cuts, this practice may result in 
-new infections. Unless the trunk and main 
limbs are threatened, it is better to postpone 
cutting until late summer or fall, when blight 
is no longer active. 
Where only a few blossoms and tips of 
branches are affected, as is so often the case 
with apple trees, little damage is done. The 
dead parts should be removed before the next 
growing season, because they often harbor 
other organisms that cause disease. 
The wounds and cuts larger than 2 inches in 
diameter may be painted with a good white-lead 
paint, with a prepared tree paint, or with a coal- 
tar-creosote paint, which may be made at home 
by thinning ordinary commercial coal tar with 
creosote oil until it has the consistency of a 
thick paint. Usually this requires about 1 part 
of creosote oil to 8 parts of coal tar. This paint 
disinfects and protects the wound or cut, but 
care should be taken not to cover live bark with 
it. Although removing holdover blight is the 
most important control measure, it will not pro- 
tect the trees of an individual orchard from be- 
coming infected if adjoining orchards contain 
holdover cankers. Old and usually worthless 
pear trees are often sources of infection for 
nearby apple orchards because of numerous 
holdover cankers. 
A chemical solution containing zinc chloride, 
which penetrates the tissues and kills the bac- 
teria, has been successfully used in some States 
as a substitute for canker removal. 
In addition, many growers use weak bordeaux 
mixture (2 pounds copper sulfate, 6 pounds 
hydrated lime in 100 gallons of water), dilute 
solutions of commercial copper spray prepara- 
tions, copper-lime dust (20 parts copper sulfate, 
80 parts hydrated lime), or zineb (1144 to 2 
pounds in 100 gallons of water) for blight con- 
trol. Streptomycin, an antibiotic, or a mixture 
of it with a small quantity of Terramycin also 
has given promising blight control. These 
materials should be applied when 25 to 30 per- 
cent of the blossoms are open and again at 7 
and at 14 days later. 
The amount of active antibiotic ingredient 
varies in the different preparations. There- 
fore, the manufacturer’s directions should be 
carefully followed in preparing these spray 
solutions. 
The application of copper-containing sprays 
or dusts during the blossom period is very apt 
to cause fruit russeting. This risk of injury 
can be avoided by the use of zineb or antibiotics 
mentioned above. No insecticide should be 
used with any of these blight-control sprays or 
dusts because of danger to bees. 
Trees of susceptible varieties are less likely 
to be seriously injured if not stimulated to rapid 
succulent growth by heavy fertilization and 
heavy pruning. 
Since the practical methods of control will 
vary somewhat in different parts of the country, 
growers should consult their county agents or 
experiment stations for methods applicable to 
their localities. 
Washington, D. C. Revised September 1954 
U. S. GOVERNMENT PRINTING OFFICE 16—70821-1 
For sale by the Superintendent of Documents, U. S. Government 
Printing Office, Washington, D. C. - Price 5cents 
