Trap and Buffer Crops

A final category in the area of cultural control as it pertains to host species other than the primary crop concerns trap crops and buffers.

Plantings used as buffers are in reality a special instance of the general category of physical barriers introduced under Section V, B, 3;

strictly speaking, the species utilized are not even hosts to the pathogens or vectors. One might go so far as to consider isolated plots, seed beds, etc., as extreme examples of protection by barriers, wherein the areas occupied by the buffer species far exceed that occupied by the host.

A more useful concept would confine the term to situations where the preponderance of area is occupied by the principal crop and the buffer is truly marginal. Forest windbreaks have been employed in part for disease control (Beilin, 1951) and presumably reduce the overland movement of air-borne inoculum. Their effect on microclimate, especially as they increase temperature and retard drying up of surface moisture, is often to increase disease hazard.

Barriers are reported effective in some instances against spread of insects to seedbeds and cropped areas. Stakman and Harrar (1957, p.

442) find some evidence that legumes sown with Hevea brasiliensis form root barriers which retard the growth of subterranean mycelium of fungi causing root rot of the rubber tree, and they suggest that similar relations might pertain to citrus, grapes, and orchard fruits. Sideris (1955) re­

counts the occurrence of a leaf tip necrosis of pineapple appearing within 1.5 miles of the sea in plantings exposed to wind-blown sea water; partial control can be achieved by establishing multiple rows of Casuarina equisetifolia on the seaward side in order to trap wind-blown sea water. The effects on pineapple can also be partly overcome by ample applications of nitrogen and potassium. Chester (1946) mentions the possibility of a rust barrier zone in the south central plains of the United States.

Use of trap or catch crops is based on the notion of providing a host species other than the primary crop, which is particularly susceptible to the pathogen, and, at an appropriate later time, destroying both host and pathogen in a single operation. By so doing it is hoped that the more valuable host will be left relatively free of the inroads of the pathogen.

In field and greenhouse trials with pineapple root knot nematode in Hawaii, Godfrey and others (Godfrey and Hagan, 1934; Godfrey and

Hoshino, 1934) found that the population could be very greatly reduced by one or more plantings of a crop such as tomato if the latter were killed at the most favorable time either by mechanical means or by poisons. Decay or destruction must come before eggs are produced or

10. CULTURAL PRACTICES IN DISEASE CONTROL 423 the net result will be to worsen rather than to reduce the population problem. These studies seemed to indicate that the best that can be hoped for is a quick reduction of heavy infections, not complete eradica-tion, and that to plant the trap crop beside the pineapple row was in-effective. Weed killers appear to be a satisfactory means of destroying the catch crop.

Berkeley (1944) includes a somewhat different type of catch or trap crop in pointing to the use of indicator plants of three different varieties in areas of Ceylon about to be replanted to Hevea rubber. The chief purpose here is not to destroy the soil pathogen but quickly to establish its presence and extent of infestation in order that diseased material may be identified, removed, and burned.

VII. S U M M A R Y AND PROGNOSIS

Several points emerge conspicuously from our consideration of cultural control. In the first place, cultural measures are a miscellany. A few are well recognized and widely adopted; many are obscure or so intricately tied in with other steps in the agricultural program that they are not accorded full credit for their contributions to crop production.

Curious anachronisms show up as one studies disease control by cultural means. It has, on the one hand, been characteristic of primitive agri-cultures, poverty of scientific information, and inadequate supplies of agricultural chemicals and equipment; on the other hand, it requires the most exacting, critical, and detailed knowledge of the biology of disease—far beyond that needed for more orthodox operations. In one sense these can be the least expensive and most rewarding of disease control efforts; in another, because the full cost is often immediately apparent and chargeable to the individual producer, cultural control is avoided as being too expensive and troublesome. Reduction of disease damage by cultural means involves more variables, is more difficult to evaluate by controlled experimentation, requires more extensive co-operative action, and impinges on the complex structure of agricultural and forest practice at more points than any alternative pathway open to the pathologist and producer.

No one can possibly say with certainty what the future will bring.

It is more than likely that there will be no sudden shift in the popularity of cultural control measures as a whole, although we can expect con-tinuing change and improvement in individual techniques. As time goes on and the knowledge of disease as a pathologic phenomenon accumu-lates, there is every likelihood that new and provocative cultural control devices will be developed and that more and more producers will take advantage of what this sector of plant pathology has to offer. More

424 RUSSELL Β. STEVENS

particularly, cultural control will continue to be important in situations where other methods prove inadequate, in cases where the biology of pathogenic disease is particularly well known, in the preservation of harvested materials and produce, in forest pathology, as an adjunct to chemical control, and, of course, in alleviating many nonpathogenic troubles. We can also hope that the economy of cultural practices will in time be more realistically evaluated and this obstacle to their wider adoption removed.

It will be immediately apparent that no complete review of the literature of disease control by cultural methods has been attempted.

In selecting the few titles to be cited in the bibliography, at least four points were emphasized: ( 1 ) where possible, reference is made to survey and review articles, thus affording access to the often very complete and far-ranging literature compilations included there and materially reducing the number of bibliographic entries in the present paper; ( 2 ) recent papers were given priority over older publications, particularly from the works of a single author; ( 3 ) emphasis was upon readily obtainable material from established sources; and ( 4 ) an effort was made to strike some sort of balance among the multiplicity of subtopics comprising the very diverse subject of cultural control.

We are greatly indebted to recent texts and monographs by Chester (1946, 1947), Stakman and Harrar (1957), and Stevens and Stevens (1952), to which a number of page references are made; and to reviews by Ν. E. Stevens (1938a) and Ν. E. Stevens and Nienow (1947).

R E F E R E N C E S

Aberg, E. 1945. Effect of vernalization on the development of stripe in barley.

Phytopathology 3 5 : 367-368.

Addicott, F. T., and R. S. Lynch. 1957. Defoliation and desiccation: harvest-aid practices. Advances in Agron. 9 : 67-93.

Allen, P. J. 1954. Physiological aspects of fungus diseases of plants. Ann. Rev.

Phnt Physiol. 5 : 225-248.

Arndt, C. H. 1945. Viability and infection of light and heavy cotton seeds. Phyto­

pathohgy 3 5 : 747-753.

Arndt, C. H. 1946. Effect of storage conditions on survival of Colletotriehum gossypii. Phytopathohgy 3 6 : 24-29.

Amy, D. C , and C. Leben. 1955. The effect of the water-soak seed treatment on the germination of certain barley varieties grown at different locations. Phyto­

pathohgy 4 5 : 518-519.

Avery, G. S., Jr., and B. F. Thompson. 1947. Chemical control of plant growth.

Econ. Botany 1 : 176-187.

Ayers, Τ. T., and Ε. B. Lambert. 1955. Controlling mushroom diseases with chlorinated water. Phnt Disease Reptr. 3 9 : 829^-836.

Baker, K. F., and committee. 1956. Development and production of pathogen-free propagative material of ornamental plants. Phnt Disease Reptr. Suppl. 2 3 8 : 57-95.

10. C U L T U R A L P R A C T I C E S I N D I S E A S E C O N T R O L 425 Baker, K. F., and W. C. Snyder. 1950. Plant diseases; restrictive effect of California

climate on vegetables, grains and flowers. Calif. Agr. 4 : 3, 15-16.

Bawden, F. C. 1954. Inhibitors and plant viruses. Advances in Virus Research 2 : 31-^57.

Bawden, F. C , and N. W. Pirie. 1952. Physiology of virus diseases. Ann. Rev. Phnt Physiol. 3 : 171-188.

Beilin, I. G. 1951. In regard to the effectiveness of forest plantings in protecting young crops from fungus diseases. Nauch. Voprosy Pohzashchitnogo Leso-Razvedeniia Inst. Lesa, Akad. Ν auk S. S. S. R. 1 : 252-264.

Berkeley, G. H. 1944. Root-rots of certain non-cereal crops. Botan. Rev. 1 0 : 67-123.

Boyer, C. A. (undated) Bramble fruit plant inspection in Michigan. 3 pp. mimeo.

Bratley, C. O., and J. S. Wiant. 1950. Diseases of fruits and vegetables found on the market, and means of controlling them. Econ. Botany 4 : 177-191.

Broadbent, L. 1957. Insecticidal control of the spread of plant viruses. Ann. Rev.

Entomol. 2 : 339^354.

Brooks, C. 1935. Some botanical aspects of perishable food products. Sci. Monthly 4 0 : 122^137.

Brown, J. G., and D. M. Heep. 1946. Effect of streptomycin on budwood infected with Phytomonas pruni. Science 1 0 4 : 208.

Brown, W. 1936. The physiology of host-parasite relations. Botan. Rev. 2 : 236-281.

Buchholtz, W. F. 1944. Crop rotation and soil drainage effects on sugar beet tip rot and susceptibility of other crops to Aphanomyces cochlioides. Phytopathohgy 3 4 : 805-812.

Chester, K. S. 1946. "The Nature and Prevention of the Cereal Rusts." Chronica Botanica, Waltham, Massachusetts. 269 pp.

Chester, K. S. 1947. "Nature and Prevention of Plant Diseases." 2nd ed. Blakiston Div., McGraw Hill, New York. 525 pp.

Chester, K. S. 1950. Plant disease losses: their appraisal and interpretation. Phnt Disease Reptr. Suppl. 1 9 3 : 191-362.

Chinn, S. H. F., R. J. Ledingham, B. J. Sallans, and P. M. Simmonds. 1953. A mechanism for the control of common rootrot of wheat. Phytopathology 4 3 : 701.

Chitwood, B. G., and B. A. Oteifa. 1952. Nematodes parasitic on plants. Ann. Rev.

Microbiol. 6 : 151-184.

Christensen, C. M. 1957. Deterioration of stored grains by fungi. Botan. Rev. 2 3 : 108-134.

Christie, J. R. 1942. The influence of chrysanthemum propagation methods on dis­

semination of the foliar nematode. Proc. Helminthol. Soc. Wash. D. C. 9 : 1—4.

Cochrane, V. W. 1949. Crop residues as causative agents of root rots of vegetables.

Conn. Agr. Expt. Sta. Bull. 5 2 6 : 34 pp.

Colwell, R. N. 1956. Determining the prevalence of certain cereal crop diseases by means of aerial photography. Hilgardia 2 6 : 223-286.

Cooley, J. S. 1946. Root diseases of deciduous fruit trees. Botan. Rev. 1 2 : 83-100.

Coons, G. H. 1953. Some problems in growing sugar beets. Yearbook Agr. U. S.

Dept. Agr. 1 9 5 3 : 509-524.

Coons, G. H., and J. E. Kotila. 1935. Influence of preceding crops on damping off of sugar beets. Phytopathology 2 5 : 13.

Darpoux, H., and A. Vuittenez. 1949. Role des peritheces de Venturia pirina dans la region parisienne. Influence de Telimination des fuilles mortes par le bechange sur Tintensite des premieres contaminations et sur revolution ulterieure de la

426 R U S S E L L Β . S T E V E N S

tavelure du Poirier. Compt. rend. acad. agr. France 3 6 : 592-594; 1950. Rev.

Appl. Mycol 2 9 : 217.

Demaree, J. B. 1948. Yellows or xanthosis in strawberries in eastern United States.

Plant Disease Reptr. 3 2 : 428-432.

DiMarco, G. R., and Β. H. Davis. 1957a. Prevention of decay of peaches with post-harvest treatments. Phnt Disease Reptr. 4 1 : 284-288.

DiMarco, G. R., and Β. H. Davis. 1957b. Prevention of decay of strawberries with post-harvest treatments. Phnt Disease Reptr. 4 1 : 460-464.

Dimock, A. W. 1951a. The dispersal of viable spores of phytopathogenic fungi by fungicidal sprays. Phytopathohgy 4 1 : 157-163.

Dimock, A. W. 1951b. Bud transmission of Verticillium in roses. Phytopathohgy 4 1 : 781-784.

Dobromyslov, P. N. 1932. Degree of infection with bunt of spring wheat grown in ridges as against flat rows. In "Diseases of Grain Crops/' Siberian Scientific-Research Institute of Cereal Economy/' Omsk. pp. 72-79; 1933. Rev. Appl.

Mycol. 1 2 : 155.

Eide, C. J. 1955. Fungus infection of plants. Ann. Rev. Microbiol 9 : 297-318.

Emmons, C .W. 1940. Medical mycology. Botan. Rev. 6 : 474-514.

Fischer, G. W., and C. S. Holton. 1957. "Biology and Control of the Smut Fungi/' Ronald Press, New York. 622 pp.

Foister, C. E. 1946. The relation of weather to fungus diseases of plants. II. Botan.

Rev. 1 2 : 548-591.

Galakhov, P. N. 1946. Measures for control of "zakuklivanie" virus disease on oats in the Subtaiga Zone of East Siberia. Dokhdy Vsesoyuz. Akad. SeVskokhoz.

Nauk im. V. I. Lenina 9 - 1 0 : 16-18; 1948. Field Crops Abstr. 1 : 34.

Gaumann, E. 1950. "Principles of Plant Infection." Hafner, New York. 543 pp.

(Engl. ed.).

Gaskill, J. O. 1950. Drying after harvesting increases storage decay of sugar-beet roots. Phytopathohgy 4 0 : 483-486.

Gillespie, W. H., A. L. Shigo, and R. P. True. 1957. The degree of mat-production control obtained by girdling oak wilt trees in West Virginia and some factors influencing mat formation in girdled trees. Phnt Disease Reptr. 4 1 : 362-367.

Godfrey, G. H., and H. R. Hagan. 1934. A study of the root-knot-nematode trap crop under field soil conditions. Phytopathohgy 2 4 : 648-658.

Godfrey, G. H., and Η. M. Hoshino. 1934. The trap crop as a means of reducing root-knot-nematode infestation. Phytopathohgy 2 4 : 635-647.

Goldsworthy, M. C , J. C. Dunegan, and R. A. Wilson. 1949. Control of apple scab by ground and tree applications. Phnt Disease Reptr. 3 3 : 312-318.

Graham, S. A. 1951. Developing forests resistant to insect injury. Sci. Monthly 7 3 : 235-244.

Graham, S. A. 1956. Ecology of forest insects. Ann. Rev. Entomol. 1 : 261-280.

Greaney, F. J. 1946. Influence of time, rate, and depth of seeding on the incidence of root rot in wheat. Phytopathohgy 3 6 : 252-263.

Groves, A. B. 1958. Root diseases of deciduous fruit trees. Botan. Rev. 2 4 : 25-42.

Hardison, J. R. 1948. Field control of blind seed disease of perennial ryegrass in Oregon. Phytopathohgy 3 8 : 404r-419.

Hart, H. 1949. Nature and variability of disease resistance in plants. Ann. Rev.

Microbiol 3 : 28&-316.

Hildebrand, Ε. M. 1953. Fruit virus diseases in New York in retrospect. Phnt Disease Reptr. Suppl. 2 2 2 : 185-223.

10. C U L T U R A L P R A C T I C E S I N D I S E A S E C O N T R O L 427 Hopkins, E. F., and K. W. Loucks. 1948. A curing procedure for the reduction

of mold decay in citrus fruits. Florida Agr. Expt. Sta. Bull. 4 5 0 : 26 pp.

Hubert, F. P. 1957. Diseases of some export crops in Indonesia. Phnt Disease Reptr.

4 1 : 55-63.

Hunt, N. R. 1946. Destructive plant diseases not yet established in North America.

Botan. Rev. 1 2 : 593-627.

Imshenetskii, Α. Α., and E. S. Nazarova. 1937. The action of ultrashort waves on wood-destroying fungi (Merulius lacrymans Schum. and Poria vaporaria Pers.).

Izvest. Akad. Nauk S. S. S. R. Ser. Biol. 1 : 221-230; 1937. Rev. Appl. Mycol.

1 6 : 721.

Kassanis, B. 1957. Effects of changing temperature on plant virus diseases. Ad­

vances in Virus Research 4 : 221-241.

Katznelson, H. 1937. Bacteriophage in relation to plant diseases. Botan. Rev. 3 : 499-521.

King, N. J. 1953. Progress in control of ratoon stunting disease. Australian Sugar J.

4 5 : 484, 486; 1954. Rev. Appl. Mycol. 3 3 : 503.

Krochmal, A. 1956. Apple storage in Northern Greece. Econ. Botany 1 0 : 174-175.

Kuijt, J. 1955. Dwarf mistletoes. Botan. Rev. 2 1 : 569-627.

Kunkel, L. O. 1955. Cross protection between strains of yellows-type virus. Advances in Virus Research 3 : 251-273.

Kuntz, J. E., and A. J. Riker. 1950. Oak wilt in Wisconsin. Wisconsin Agr. Expt. Sta.

Stencil Bull. 9 : 9 pp.

Large, E. C. 1940. "The Advance of the Fungi." Holt, New York. 488 pp.

Lear, B., and W. F. Mai. 1952. Methyl bromide for disinfesting burlap bags and machinery to help prevent spread of golden nematode of potatoes. Phyto­

pathology 4 2 : 489-492.

Leben, C , R. W. Scott, and D. C. Arny. 1956. On the nature of the mechanism of the water-soak method for controlling diseases incited by certain seed-borne pathogens. Phytopathology 4 6 : 273-276.

Leighty, C. E. 1938. Crop rotation. Yearbook Agr. U. S. Dept. Agr. 1 9 3 8 : 406-430.

Levy, B. G. 1948. Certification schemes for fruit plants. Ann. Rept. East Mailing Research Sta. Kent 1 9 4 7 : 178-181; 1949. Rev. Appl. Mycol. 2 8 : 34CM541.

Loehwing, W. F. 1937. Root interactions of plants. Botan. Rev. 3 : 195-239.

McGrath, H. and P. R. Miller. 1958. Blue mold of tobacco. Phnt Disease Reptr.

Suppl. 2 5 0 : 1-35.

Mader, E. O. 1947. A corrective measure for "soil sickness" occurring in sand media.

Phytopathohgy 3 7 : 682-683.

Martin, W. J., J. M. Lutz, and G. B. Ramsey. 1949. Control of black rot in washed, uncured sweet potatoes. Phytopathology 3 9 : 580-582.

Mather, S. M. 1952. Strawberry plant certification and registration in California.

Calif. Dept. Agr. Bull. 4 1 : 3-8.

Metlitskii, L., and V. Soboleva. 1936. The lethal action of high frequency field on Sclerotinia Libertiana and Botrytis cinerea. Zashchita Rastenfi 1 0 : 32-36.

Milbrath, D. G. 1948. Control of Western celery mosaic. Calif. Dept. Agr. Bull. 3 7 : 3-7.

Miles, L. E. 1939. Effect of type and period of storage on cotton seed after treatment with organic mercury dust. Phytopathology 2 9 : 986-991.

Miller, Ε. V. 1946. Physiology of citrus fruits in storage. Botan. Rev. 1 2 : 393-423.

Moore, W. D. 1949. Flooding as a means of destroying the sclerotia of Sclerotinia sclerotiorum. Phytopathology 3 9 : 920-927.

428 R U S S E L L Β . S T E V E N S

Morgan, Ε. P. 1948. Food's paradise. Colliers 1 2 1 : (18) 18-19, 40-42.

Morris, C. L. 1955. Control of mat formation by the oak wilt fungus by early felling of diseased trees. Phnt Disease Reptr. 3 9 : 258-260.

Newhall, A. G. 1955. Disinfestation of soil by heat, flooding and fumigation. Botan.

Rev. 2 1 : 189-250.

Newton, N. 1951. Some effects of high-intensity ultrasound on tobacco mosaic virus.

Science 1 1 4 : 185-186.

Painter, R. H. 1958. Resistance of plants to insects. Ann. Rev. Entomol. 3 : 267-290.

Parkin, E. A. 1956. Stored product entomology (the assessment and reduction of losses caused by insects to stored foodstuffs). Ann. Rev. Entomol. 1 : 223-235.

Pentzer, W. T., and P. H. Heinze. 1954. Postharvest physiology of fruits and vegetables. Ann. Rev. Phnt Physiol. 5 : 205-224.

Peterson, P. D., and H. W. Johnson. 1928. Powdery mildew of raspberry. Phyto­

pathohgy 1 8 : 787-796.

Piemeisel, R. L. 1954. Replacement control; changes in vegetation in relation to con­

trol of pests and diseases. Botan. Rev. 2 0 : 1-32.

Pound, G. S. 1946. Control of virus diseases of cabbage seed plants in Western Washington by plant bed isolation. Phytopathohgy 3 6 : 1035-1039.

Rodenwaldt, E. (ed.) 1952-1955. "World Atlas of Epidemic Diseases," Vols. 1, 2, 3.

Falk, Hamburg.

Schomer, Η. Α., and L. P. McColloch. 1948. Ozone in relation to storage of apples.

U. S. Dept. Agr. Circ. 7 6 5 : 24 pp.

Schultz, E. S., R. Bonde, and W. P. Raleigh. 1944. Early harvesting of healthy seed potatoes for the control of potato diseases in Maine. Maine Agr. Expt. Sta. Bull.

4 2 7 : 19 pp.

Sideris, C. P. 1955. Effects of sea water sprays on pineapple plants. Phytopathohgy 4 5 : 590-595.

Simmonds, P. M. 1953. Rootrots of cereals. II. Botan. Rev. 1 9 : 131-146.

Smith, F. F., and P. Brierley. 1956. Insect transmission of plant viruses. Ann. Rev.

Entomol 1 : 299-322.

Smith, H. S., E. O. Essig, H. S. Fawcett, G. M. Peterson, H. J. Quayle, R. E. Smith, and H. R. Tolley. 1933. The efficacy and economic effects of plant quarantine in California. Calif. Agr. Expt. Sta. Bull. 5 3 3 : 276 pp.

Smock, R. M. 1944. The physiology of deciduous fruits in storage. Botan. Rev. 1 0 : 560-598.

Snelling, R. O. 1941. Resistance of plants to insect attack. Botan. Rev. 7 : 543-586.

Stakman, E. C , and J. G. Harrar. 1957. "Principles of Plant Pathology." Ronald Press, New York. 581 pp.

Steinbauer, G. P., and F. H. Steinmetz. 1945. Eradication of certain Maine weeds, an important step in control of potato diseases spread by aphids. Maine Agr.

Expt. Sta. Misc. Publ. 6 0 2 : 21 pp.

Stevens, Ν. E. 1938a. Departures from ordinary methods in controlling plant diseases.

Botan. Rev. 4 : 429-445, 677-678.

Stevens, Ν. E. 1938b. Problems involved in control of plant diseases and insects. J.

Econ. Entomol 3 1 : 39-44.

Stevens, Ν. E. 1940. Recent trends in plant disease control. Trans. Illinois State Acad.

Sci. 3 3 : 66-67.

Stevens, Ν. E. 1942. How plant breeding programs complicate plant disease prob­

lems. Science 9 5 : 313-316.

Stevens, Ν. E. 1949. Characteristics of some disease-free ornamental plants. Science 1 1 0 : 218-219.

10. CULTURAL PRACTICES IN DISEASE CONTROL 429 Stevens, Ν. E., and I. Nienow. 1947. Plant disease control by unusual methods.

Botan. Rev. 13: 116-124.

Stevens, Ν. E., and R. B. Stevens. 1952. "Disease in Plants." Chronica Botanica, Waltham, Massachusetts. 219 pp.

Stevens, R. B. 1949. Replanting "discarded" varieties as a means of disease control.

Science 110: 49.

Stoner, W. N., and W. D. Moore. 1953. Lowland rice farming, a possible cultural control for Sclerotinia sclerotiorum in the Everglades. Phnt Disease Reptr. 37:

181-186.

Stout, G. L. 1950. New methods of plant disease control. Calif. Dept. Agr. Bull. 39:

129-136.

Tandon, I. N., and E. D. Hansing. 1957. Control of loose smut of barley by water-soak and anaerobic treatments. Phnt Disease Reptr. 4 1 : 202-204.

Tapke, V. F. 1948. Environment and the cereal smuts. Botan. Rev. 14: 359-412.

Tyner, L. E. 1953. The control of loose smut of barley and wheat by Spergon and by soaking in water at room temperature. Phytopathohgy 43: 313-316.

Valleau, W. D. 1953. Suggestions for more complete control of downy mildew or blue mold of tobacco. Phytopathohgy 43: 616-618.

Vaughan, Ε. K. 1956. A method for eliminating the red-stele fungus from valuable strawberry stocks. Phytopathohgy 46: 235-236.

Verrall, A. F. 1945. The control of fungi in lumber during air-seasoning. Botan. Rev.

11: 398-415.

Wagener, W. W., and R. W. Davidson. 1954. Heart rots in living trees. Botan. Rev.

20: 61-134.

Waggoner, P. E. 1958. Private communication.

Walker, J. C. 1941. Disease resistance in the vegetable crops. Botan. Rev. 7: 458-506.

Weiss, F. 1949. Weeds, fungi, and the education of botanists. Sci. Monthly 68: 257-261.

Wilson, Ε. E., and G. A. Baker. 194Q. Some features of the spread of plant diseases by air-borne and insect-borne inoculum. Phytopathohgy 36: 418-432.

Wilson, J. D. 1932. Environmental factors in relation to plant disease and injury:

a bibliography. Ohio Agr. Expt. Sta. Tech. Ser. Bull. 9: 203 pp.

Wingard, S. A. 1941. The nature of disease resistance in plants. I. Botan. Rev. 7:

59-109.

Wood, J. I., and P. R. Miller. 1949. Losses from plant diseases: effects on crop industries and on farm life. Phnt Disease Reptr. Suppl. 186 : 254r-282.

Yarwood, C. E. 1945. Copper sulphate as an eradicant spray for powdery mildew.

Phytopathohgy 35: 895-909.

Yarwood, C. E. 1957. Powdery mildews. Botan. Rev. 23: 235-301.

In document Cultural Practices in Disease Control (Pldal 66-73)