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A Brief Handbook of the Diseases of Cultivated Plants in Ohio

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A Brief Handbook of the Diseases of Cultivated Plants in Ohio Cornell "University OF THE flew jporfe State (Tolleoe of Horiculture \^.^r23.a Cornell University Library SB 624.03S4 diseases of cult A brief handbook of the Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003214529 BULLETIN OF THE Ohio Agricultural Experiment Station Number 214 ' March, 1910. A BRIEF HANDBOOK OF THE DISEASES OF CULTIVATED PLANTS IN OHIO By A. D. SELBY INTRODUCTION The idea of disease is not a simple one, though it may seem so before trying to define it. In reality the term "disease" as applied to plants, means any change in that plant toward reduced vigor, etc., from the ordinary or average behavior. To put it another way, a plant is said to be "diseased" when it shows any deviation from the ordinary or average behavior of that plant in respect to appearance, growth, color of bark, foliage, fruitfulness, time of dropping leaves or length of life; in short, when the plant fails to conform to those averages which we have established by extended observation for the species and variety in question, we say it is diseased. Under such a general definition, variegated or purple hued sports would be included, although potentially rather than actually in diminished succumb easily to parasitic attack and, as - vigor. Variegated sports later investigations show, are really suffering from enzymatic troubles. The more usual symptoms of disease are marked by evident curled or differences in the plant. The leaves become spotted, the fruit may develop discolored, or may even drop prematurely; twigs may blight, unevenly or be marked by decayed spots, or the a manifest loss of vigor and wilt or die. In all such cases we have attribute all these to parasitic reduced profit. Yet we may not physical or chemical agencies fungi or to parasitic insects; purely troubles. Plants may be as- may be at the bottom of certain excludes the air supply; they phyxiated by too much water which gases, especially in the case may likewise, be strangled by escaping protoplasm may be attacked by chemi- of city shade trees, or their (307) 308 OHIO EXPERIMENT STATION: BULLETIN 214 cal agents such as strong acids and alkalis. Quick growing plants appear to fall in drought, as with cucumbers when started during a period of excessive rains. Plants, and especially trees, may be locally injured by winter freezing, by hail, by overbearing with ex- haustion of water supply, and by a variety of causes. While we must keep our minds open to these varying causes of impaired vigor, by far the larger number of the diseases described in this bulletin are directly attributable to parasitic fungi which attack the plant or host in some vital part and rob it of its substance. The conditions of injury arising from the attacks of insects alone are not included. These fungus parasites of particular plants are of differing sorts, which produce, each, its more or less particular effects. It must follow, therefore, that the diseases produced differ in nature and that the names applied will vary accordingly. The names are not simply blight, rust, etc., indiscriminately applied—they are given with reference both to the parasite and its effect on the host plant.* Parasitic fungi and bacteria which cause disease, being plants, though of lower class, have differences among themselves which may be clearly designated and defined. The names applied to them are accompanied by specific and generic descriptions which mark off the sort as definitely as do the descriptions on higher plants such as ferns, flowering plants and trees. The extreme minuteness of the parts of parasitic fungi and bacteria make necessary the use of the microscope in their description and detection. The parts called spore's which reproduce these minute plants have special form, size, etc., by which these are recognized when found. The agencies for the spread of parasitic diseases are those operations in which we engage or those which surround and envelop the plants as well as ourselves. Light spores will be carried by currents of air like particles of dust. All spores or germs of these lower plants may be carried by numerous agencies such as insects, higher animals, and man. They will also find entrance into plants by whatever openings exist at the time. The epidermis of a green leaf or stem has breathing pores or stomatesinit; the leaves of mustard plants have water pores in them and wounded plants have these fresh openings to invite the entrance of the disease conveying spores or germs. The remedies for plant diseases are based upon the character and life history of the particular parasitic growth with which we have to deal and upon the nature of the host plant itself—some hosts being very different from others in respect to permitting of sprays of fungicides or insecticides. Common sense inferences are * See naming of diseases. DISEASES OP CULTIVATED PLANTS 309 always of use in dealing with plant diseases. If the soil is too wet, drain it; if late growth predisposes to winter injury, avoid such growth; if overbearing weakens plants, prevent, it by thinning the fruit. The philosophy of seed treatments is stated under diseases which infest the seed; that of soil treatments or disinfection, under soil infesting disease, and the general doctrines of sprays, fungi- cides, etc., under that heading further on. The progress made in plant disease prevention throughout the world during the period of about 26 years which has elapsed since the discovery of Bordeaux mixture in France shows how well adapted that discovery was to the needs of the times. The progress made in recent years in the study and control of plant diseases has been made possible by the agencies recently developed in the United States in the Agricultural Colleges, the Agricultural Experiment Stations and the United States Depart- ment of Agriculture. It is not expected that this advance in our knowledge of the diseases of plants or of the methods of disease control will soon wane. Efforts like the present one to present briefly the doctrines of disease and the philosophy of disease con- trol together with brief descriptions of prevailing diseases in our state, have for their purpose the wider dissemination of the body of present day knowledge in f/x 2 lines. Such a statement will not close the march of progr nor make less the need for more knowledge. It is hoped t i cultivators of plants, whether farmers, gardeners, horticulturists or florists v/ill find suggestive statements of information in the bulletin by which they can direct their own efforts to better advantage and correct or broaden their own in- ferences from observed conditions about them. All such results will not only increase the need for more knowledge, but will furnish impetus to the movements by which we will gain the desired information. In the preparation of the revised edition of the original Bulletin, No. 121, the general part immediately following this introduction has been considerably enlarged and brief discussions are now given concerning groups of plant diseases as well as those concerning parasitic fungi. It is fully apprehended that the host plant is the center of practical as well as economic interest and these statements concerning enzymatic diseases as in the case of peach yellows and mosaic disease of tobacco, diseases transmitted in the seed, soil infesting diseases, and the relation of the spread of certain diseases to leaf biting insects are given as aids in mastering the principles involved. The same aim has governed the discussions upon wounds 310 OHIO EXPERIMENT STATION: BULLETIN 214 and wound fungi so especially dangerous with orchard, shade and forest trees. Somewhat fuller discussion of atmospheric agencies as affecting ;the occurrence and spread of plant diseases, of remedies for diseased conditions and of the application of the latter in combatting diseases and a presentation of storage troubles has also seemed desirable. Special attention is called to the host plant in the matter of breeding or selection for disease resistance and in the contrasts offered by American and European points of view in plant disease study. ACKNOWLEDGMENTS The illustrations in this bulletin have been drawn from wider sources than in the previous hand book. A large number, including perhaps, a larger portion of the cuts, are taken from previous pub- lications of this Station by Weed, Miss Detmers, and the writer; small cuts have been at times made from certain larger illustrations while with others only portions of the original cut have been used. A great many of the illustrations are new, and I am deeply in- debted to Messrs. J. M. Van Hook and Thos. F. Manns for many of the photographs from which these have been made. I am also in- debted to Professors Halsted of New Brunswick, N. J., and Atkin- son of Ithaca, N. Y., and to the Bureau of Plant Industry of the U.S. Department of Agriculture for many favors in the matter of cuts which are used in the Bulletin. Figures 24, 25, and 26 are from Dr. Freeman's "Minnesota Plant Diseases." For permission to reproduce these, I am indebted to Prof. Frederick E. Clements, of the University of Minnesota. In all cases where it is not otherwise obvious, it has been the aim to state the source of the illustrations in the descriptions. The same applies to illustrations reproduced from standard works. In many matters connected with recent investigations of the Department bearing upon diseases included in this present bulletin, and upon current examinations, I am under many obligations to Thos.
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