BUREAU OF PLANT INDUSTRY. 217 



diseases caused by fungi, microbes, and insects. The matter is one 

 of much greater importance than is even yet commonly supposed, 

 and the establishment of definite facts connected with the problem is 

 highly desirable, in order that laws, regulations, and other remedies 

 may be devised, amended, and applied. 



During the course of these investigations several exceedingly seri- 

 ous diseases caused by ncmas have been detected Avhen about to be 

 imported into this country. The matter is therefore not one of theory 

 but of conditions definitely known to exist. 



FRUIT-DISEASE INVESTIGATIONS. 



FRUIT DISEASES. 



Apple scab, apple leaf-spot, cherry leaf-blight, and many other 

 fungous diseases of deciduous orchards in the eastern half of the 

 United States were very nuicli less severe in the spring of 1920 than 

 the previous year, mainly on account of favorable weather, a rather 

 drv and sunny April and May. 



!t*ear-bliglit over a large part of the country both east and west, 

 but particularly over the eastern half of the United States, showed a 

 great falling off in severity during the spring of 1920. It was less 

 serious than normal in most sections during 1919, but the great out- 

 break which began in 1914 gradually declined until there is much 

 less trouble than normal from this disease. It still has caused seri- 

 ous destruction in certain localities. 



The form known as collar blight was unusually severe in the sum- 

 mer of 1919 in the Pacific Xorthwest, and research and service work 

 was carried out in that section. Serious losses have occurred from 

 collar blight in apple orchards, particularly on the Grimes and 

 Esopus. Assistance was rendered in diagnosing and eradicating the 

 disease. Advice has previously been given in planting new orchards 

 to circumvent this disease by planting resistant varieties and then 

 top-working. This can be done in tlie nursery by biulding 2 or 3 

 feet above the ground, or, still better, it can be done in the orchard 

 by top-working six or moro branches after the trees have grown two 

 to four years. Immune or resistant varieties have little or no trouble 

 from collar blight, and experience is gradually accumulating on top- 

 worked Grimes in the East showing the success of this plan. 



To solve the collar-blight problem of the trees of these susceptible 

 varieties already growing in the orchard a neAV method has been de- 

 vised and proposed by which bridge grafting is utilized and the bark 

 of the susceptible sort removed and replaced by scions of the resistant 

 sorts. The susceptible collars of these trees, therefore, will be 

 worked over until a result equivalent to the resistant stocks is ob- 

 tained. Tliis method will be tested next spring. 



Aj)ple ( edar rust in the eastern United States continues to be an 

 inipoitaut problem. Tlie disease was unusually severe last season 

 and therefore renewed attention was given during the fall and winter 

 to the removal of cedar trees, Avhich are dangerous in the vicinity 

 of orchards Avhen this fungus is })resent. Last year's experience 

 showed that 1 mile was not sufficient where abundant cedars occur, 

 a greater distance for cedar removal being re(]uired. This season, 

 in common with otlier spring fungous diseases, cedar ru.st was much 

 less abunthint than it has been for several years past. 



24435— AGB 1920 15 



