8 BULLETIN 712^ U. S. DEPAETMENT OF AGEICULTURE. 



to watersprouts and terminals and has not been observed to be as 

 severe as that often met with in the irrigated regions. Wliere apple 

 scab is prevalent, as in these more humid sections of the Northwest, 

 the ordinar}' sprayings with lime-sulphur solution for scab control 

 are effective against mildew, and its control in these sections, there- 

 fore, presents no unusual difficulty. In such districts as the Spokane 

 Valley, Wash., the Hood Elver valley, Oreg., and other sections 

 where natural rainfall can be relied upon for part of the mois- 

 ture necessary for tree growth and where spraying for apple scab is 

 generally practiced, the growers and horticultural inspectors are 

 agreed that apple powdery mildew is of little or no economic im- 

 portance. However, in the hot interior valleys, where irrigation 

 is entirely depended upon for moisture supply and where fungicidal 

 spraying has been regarded as unnecessary, the disease has demanded 

 serious attention, and the development of a safe and effective spray- 

 ing schedule has been attended with peculiar difficulties. Reports 

 of the State horticultural inspectors indicate that serious loss is often 

 experienced. Mr. C. W. Gilbreath, State horticultural inspector in 

 the Walla Walla (AVash.) district, is authority for the following 

 statement regarding the disease : 



The damage from apple powdery mildew in this district grew heavier each 

 succeeding year and reached its maximum in 1915. As a result many orcliards 

 showed a reduction in crop of 25 to 50 per cent. Jonathan and Newtown are the 

 most susceptible varieties. 



That the disease is equally serious in the Yakima Valley, Wash., 

 where the largest acreage of apple orchards in the Northwest is 

 found, is indicated by the following statement of Mr. H. E. Water- 

 bury, State horiticultural inspector for the district: 



Mildew, is prevalent all over the valley on certain varieties, such as Jona- 

 than, Spitzenburg, Newtown, and Rome. The loss occasioned is chiefly loss in 

 vitality, which can scarcely be measured. I do not know of any orchards that 

 do not have some mildew. There has been considerable loss from the so-called 

 mildew scratches (russeting) on the fruit, which has reduced the grade. In 

 some places the Black Ben Davis was so badly marked that fully 25 per cent 

 had to be culled. 



Observations by the writer in the Wenatchee Valley indicate that 

 orchards often have shown a reduction of fully 75 per cent of the 

 crop as a result of mildew infection and that frequently nearly all 

 of the new wood growth is attacked, while foliage infection may 

 reach 75 to 90 per cent. Its damage was most severe in many parts 

 of the valley in 1914 and 1915, but each year sees appreciable losses 

 in some orchards due to mildew infection. In 1915 many crops of 

 Jonathan and Black Ben Davis were complete failures, due to the 

 severity of the 1914 infection, while many other varieties were 

 seriously damaged through fruit russeting, foliage infection, and 

 twig blighting. Alarm over impending damage became so general 



