4 LEAFLET 187, U. S. DEPARTMENT OF AGRICULTURE 



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 when blight is no longer active.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, but the dead 

 parts should be removed before the next growing season, not only 

 because they are unsightly but 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 thin- 

 ning 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 3 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 hold-over blight is the most important 

 control measure, it will not protect the trees of an individual 

 orchard from becoming infected through the medium of hold-over 

 cankers in adjoining orchards. Old and usually worthless pear trees 

 are often sources of infection for near-by apple orchards because of 

 numerous hold-over cankers. 



A chemical solution containing zinc chloride, which penetrates the 

 tissues and kills the bacteria, has been successfully used in some 

 States as a substitute for canker removal. Chemical treatment is a 

 rapid method of eliminating infected tissues, but it requires great 

 skill and care. For specific directions growers should consult county 

 agents or State experiment stations. 



In recent years a weak bordeaux mixture composed of 1 pound of 

 copper sulfate, 3 pounds of hydrated lime, and 50 gallons of water, 

 applied as a spray at least once during the blossoming season, has been 

 widely tested as a supplement to the "cutting-out" control measure. 

 Although this spray has not always proved useful and is apt to cause 

 injury that later may develop into fruit russeting, it is worthy of trial 

 on trees that in previous years have been so subject to blight that 

 they have not been profitable. If a single application is made, it 

 should be made when 75 to 80 percent of the blossoms are open; if two 

 applications are made, the first should be made when 25 to 35 percent 

 of the blossoms are open, and the second as above. These applica- 

 tions will also aid in the control of scab. No arsenate of lead should 

 be used in either application, because of the danger to bees. The 

 sprays usually applied for the control of sucking _ insects, such as 

 aphids, are useful in cutting down the number of insect carriers of 

 blight. 



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 dif- 

 ferent parts of the country, growers should consult their county 

 agents or experiment stations for methods applicable to their localities. 



158505° — 39 U. S. GOVERNMENT PRINTING OFFICE: 1939 



For sale by the Superintendent of Documents, Washington, D. C. - - - - Price 5 cents 



