26 MASS. EXPERIMENT STATION BULLETIN 369 



wettable sulfurs emphasizes the importance of proper timing and thorough spray- 

 ing rather than the material usea. When the fruit was examined for apple scab, 

 a record of injury by the plum curculio was also made and the results show that 

 bentonite sulfur, as represented b\' Kolofog, which provided the heaviest deposit 

 and the most persistent adherence of residue, gave the best control of the curculio. 

 2. Copper Sprays for Vegetables. The cucumber plots were destroyed by 

 mosaic before there were any appearances of downy mildew. Some rows re- 

 mained green longer than others but the untreated plot outyielded all others. 

 Higher yields were not necessarily associated with low percentages of mosaic 

 cucumbers. With melon, downy mildew appeared late and in spite of the disease 

 the highest yield was obtained from the unsprayed row. Drought conditions 

 were unfavorable for tomato foliage diseases; nevertheless, there were wide 

 differences in yield among the dilTerent treatments. With celery, 67.4 percent 

 of the leaflets in the unsprayed rows were affected with late blight, as compared 

 to less than 1 percent in the sprayed rows. 



Diseases of Trees in Massachusetts. (M. A. McKenzie and A. Vincent Osmun.) 



The Dutch Elm Disease Problem. In view of the imminence of the Dutch elm 

 disease, which has increased in 1939 with the steady encroachment of the disease 

 to a point in New York less than five miles from the southwestern border of 

 Massachusetts, studies of tree diseases in the field and in the laboratory have 

 accorded special attention to those diseases of elms which superficially are not 

 to be distinguished from the Dutch elm disease. 



Present studies of the spread of the Dutch elm disease in the United States 

 indicate new locations for the causal fungus in parts of the States of New York, 

 Connecticut, Pennsylvania, and Maryland in Eastern United States; and at 

 stations in Ohio and Indiana in the Midwest. Connecticut, with 348 affected 

 trees reported for the year, remained the only New England State in which the 

 Dutch elm disease is known to occur. Since the first discovery of the disease in 

 America, approximately 57,000 trees have been removed in the United States 

 because they were afflicted with the pestilence, and about 4,109,300 additional 

 undesirable or dead elms have been removed from zones immediately surrounding 

 infestations. The 1939 figures for the entire country show a decrease of 40 per- 

 cent in the number of diseased trees as compared with 1938. From the standpoint 

 of Massachusetts, however, the pro.ximity of the disease is particularly discon- 

 certing in spite of the decrease in the number of diseased trees. 



Interested agencies, groups, and individuals, including the Federal Bureau of 

 Entomology and Plant Quarantine, the Massachusetts Forest and Park Associa- 

 tion, arboriculturists, employees in other State and Municipal departments, and 

 private citizens have supplemented the work of this organized project in collecting 

 specimens from trees showing symptoms resembling those of the Dutch elm disease. 

 On two occasions during the summer, the elms in Berkshire County were the 

 subject of intensive scouting by trained scouts from this Laboratory. Samples of 

 trees suspected of harboring the disease were collected also in Hampden, Hamp- 

 shire, and parts of Franklin and Worcester Counties. Up to the present time 

 (November 28, 1939) the Dutch elm disease has not been found in Massachu- 

 setts. All reports that the disease was present in the State have been investigated 

 and found to be without basis in fact. 



Considerable confusion exists as to what constitutes the Dutch elm disease. 

 Any accurate statement relative to the occurrence of the disease must include 

 the laboratory report of cultural isolation of the causal fungus from affected trees. 

 Because of the close association of certain carrier insects with the spread of the 

 causal fungus and the control measures directed against them, statements con- 

 cerning these insects have sometimes been misinterpreted as relating to the 



