. Bulletin of the Department of Agriculture. Agriculture; Agriculture. BULLETIN No. 712 Contribution from the Bureau of Plant Industry WM. A. TAYLOR, Cliief. Washington, D. C. PROFESSIONAL PAPER October 29, 1918 APPLE POWDERY MILDEW AND ITS CONTROL IN THE ARID REGIONS OF THE PACIFIC NORTHWEST.^ By D. F. Fisher, Assistant Pathologist, Fruit-Disease Investigations. CONTENTS. Economic importance of powdery mildew 1 Review of the literature 2 The causal organism 4 Dissemination of the fungus 5 Description of the disease 6 SusceptibUity of varieties 7 Importance of the disease in the Pacific N
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. BULLETIN No. 712 Contribution from the Bureau of Plant Industry WM. A. TAYLOR, Cliief. Washington, D. C. PROFESSIONAL PAPER October 29, 1918 APPLE POWDERY MILDEW AND ITS CONTROL IN THE ARID REGIONS OF THE PACIFIC NORTHWEST.^ By D. F. Fisher, Assistant Pathologist, Fruit-Disease Investigations. CONTENTS. Economic importance of powdery mildew 1 Review of the literature 2 The causal organism 4 Dissemination of the fungus 5 Description of the disease 6 SusceptibUity of varieties 7 Importance of the disease in the Pacific North- west 7 Spray injury .â 9 Orchard spraying experiments 10 Sprayiug experiments in 1915 12 Orchard spraying experimentsâContd. Spraying experiments in 1916 15 Spraying experiments in 1917 17 Injury to fruit and foliage 20 Spray materials 21 Summary of control measures 23 Dormant sprays 23 Pruning experiments 24 General notes on the control of the disease 25 Conclusions 26 Literature cited 28 ECONOMIC IMPORTANCE OF POWDERY MILDEW. Apple powdery mildew is usually considered as of only minor im- portance and principally affecting nursery stock in the eastern part of the United States, only becoming serious in restricted localities. Occasionally it is severe in Utah, Colorado, New Mexico, and the East on old trees, but in the apple-growing districts of the Pacific coast the conditions are such that it often becomes serious. The arid climate of the hot interior valleys of the Pacific Northwest has proved an effective safeguard against fungous diseases in general, but apple powdery mildew is endemic. In these regions, where deciduous-fruit growing, and especially apple growing, has become such an important industry, orcharding is generally carried on under very intensive conditions and the in- 1 Acknowledgment is due Dr. Charles Brooks, of the Office of Fruit-Disease Investiga- tions, Bureau of Plant Industry, for many helpful suggestions during the course of the work, and to M
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