2Disease ProgressDisease on plants usually starts out at a low level, a small number of plants affected and a small amount of plant tissue affected, and it becomes of concern to us only when its incidence and severity increases with time.
3Disease ProgressWhen we look at some examples of plant disease epidemics from the published literature, we not only notice that the incidence or severity starts near zero and then increases dramatically, but we also can discern some distinct patterns of development with time.
4Disease ProgressFor example, in Phytophthora blight of pepper seedlings (Phytophthora capsici) and Fusarium kernel rot (Fusarium moniliforme) of maize, disease progress is roughly linear (allowing for some minor deviations that we can consider random error)
7Disease ProgressOn the other hand, in bean rust (Uromyces phaseoli) and grey leaf spot of corn (Cercospora zeae-maydis), there is a definite upward curve; that is, disease increases at an increasing rate, a curve we could call exponential.
10Disease ProgressObviously plant disease cannot continue to increase forever, and as the level of disease approaches 100%, the disease progress curve gradually flattens out. For example, in epidemics such as the infection of beans by Sclerotium rolfsii or the infection of tobacco by Phytophthora parasitica var. nicotianae, disease progress starts out looking linear but slows down as it approaches a maximum.
13Disease ProgressLikewise, the disease progress curves of Puccinia graminis subsp. graminicola on ryegrass and Pyrenophora teres f. sp. teres on barley appear exponential at first, but as time goes on and the incidence and severity of disease approach 100%, the rate of disease progress gradually slows to zero, giving both curves a somewhat sigmoid shape ("S" shape).
16To be sure, not all examples of disease progress can be as neatly categorized as these, but in general plant disease epidemics tend to be either roughly linear or exponential in the early stages, and they tend to level off as they approach some limit.
17The impact of plant disease and the losses that it causes are a function of disease progress. To reduce this impact, we need not eliminate the disease, we merely need to keep disease development below an acceptable level. That means that the progress of disease and the factors that influence disease progress must be understood in quantitative terms.
18We have to know :what kinds of diseases lead to linear disease progress and what factors affect the slope of the line (the rate of disease progress) what kinds of diseases tend to produce exponential disease progress curves and how we can reduce both the starting level of disease and the rate of epidemic development why epidemics sometimes level off and what imposes limits to their development.
19The Cyclical Nature of Plant Disease Plant disease epidemics are cyclical phenomena, that is, they consist of repeated cycles of pathogen development in relation to the host.
20The inoculum, which might consist of fungal spores, bacterial cells, nematodes, viruses within an aphid vector, or some other propagules of a pathogen,gains entry into and establishment within the host tissues through the process of infection.
21The pathogen develops within the host and eventually begins to produce new inoculum, which, in turn, can be dispersed to new susceptible sites to initiate new infections.
22Pathogens that produce only one cycle of development (one infection cycle) per crop cycle are called monocyclic, while pathogens that produce more than one infection cycle per crop cycle are called polycyclic.
23Generally in temperate climates there is only one crop cycle per year, so the terms "monocyclic" and "polycyclic" are based on the number of cycles per year. In tropical or subtropical climates, however, there can be more than one crop cycle per year, and it is important to remember that "monocyclic" and "polycyclic" are based on a single crop cycle. These same terms are used to describe the epidemics as well as the pathogens, so we often speak of a "monocyclic epidemic" or a "polycyclic epidemic".
24Epidemic:"Change in disease intensity in a host population over time and space.“
25Change : often increase -- a dynamic process Disease : dealing with diseases, not just the pathogen (or plant/crop)Host : Organism infected (or potentiallyinfected) by another organismPopulation : a population phenomenonTime and space : two physical dimensions of interest.
26Epidemiology:• Study of epidemics.• Science of disease in populations.• Ecology of disease.• Study of the spread of diseases, in space and time,with the objective to trace factors that areresponsible for, or contribute to, epidemicoccurrence.• The science of populations of pathogens inpopulations of host plants, and the diseasesresulting therefrom under the influence ofthe environment and human interferences.
28All plant diseases result from a three-way interaction between the host, the pathogen and the environment.An epidemic develops if all three of these factors are favourable to disease development.Therefore, disease can be controlled by manipulating one or more of these factors so that conditions are unsuitable for replication, survival or infection by the pathogen.
29Since the beginning of agriculture, generations of farmers have been evolving practices for combating the various plagues suffered by our crops. Following our discovery of the causes of plant diseases in the early nineteenth century, our growing understanding of the interactions of pathogen and host has enabled us to develop a wide array of measures for the control of specific plant diseases.
30From this accumulated knowledge base, we can distill some general principles of plant disease control that can help us address the management of new problems on whatever crop in any environment.
31One such set of principles, first articulated by H. H One such set of principles, first articulated by H. H. Whetzel in 1929 and modified somewhat by various authors over the years, has been widely adopted and taught to generations of plant pathology students around the world. These "traditional principles", as they have come to be known, were outlined by a committee of the US National Academy of Sciences, 1968.
32Traditional Principles of Plant Disease Control Avoidance—prevent disease by selecting a time of the year or a site where there is no inoculum or where the environment is not favorable for infection. Exclusion—prevent the introduction of inoculum. Eradication—eliminate, destroy, or inactivate the inoculum. Protection—prevent infection by means of a toxicant or some other barrier to infection. Resistance—utilize cultivars that are resistant to or tolerant of infection. Therapy—cure plants that are already infected.
33While these principles are as valid today as they were in 1929, in the context of modern concepts of plant disease management, they have some critical shortcomings.First of all, these principles are stated in absolute terms (e.g., "exclude", "prevent", and "eliminate") that imply a goal of zero disease. Plant disease "control" in this sense is not practical, and in most cases is not even possible. Indeed, we need not eliminate a disease; we merely need to reduce its progress and keep disease development below an acceptable level. Instead of plant disease control, we need to think in terms of plant disease management.
34A second shortcoming is that the traditional principles of plant disease control do not take into consideration the dynamics of plant disease, that is, the changes in the incidence and severity of disease in time and space. (See: Disease Progress.)
35Furthermore, considering that different diseases differ in their dynamics, they do not indicate the relative effectiveness of the various tactics for the control of a particular disease. They also fail to show how the different disease control measures interact in their effects on disease dynamics. We need some means of assessing quantitatively the effects of various control measures, singly and in combination, on the progress of disease.
36Finally, the traditional principles of plant disease control tend to emphasize tactics without fitting them into an adequate overall strategy.Does this mean that we should abandon the traditional principles? Of course not! We merely have to fit them into an appropriate overall strategy based on epidemiological principles.
37The Epidemiological Basis of Disease Management Plant disease epidemics can be classified into two basic types, monocyclic and polycyclic, depending on the number of infection cycles per crop cycle. (See: The Cyclical Nature of Plant Disease.)
38The early stages of a monocyclic epidemic can be described quite well by a linear model, while the early stages of a polycyclic epidemic can be described with an exponential model. Since we are concerned with keeping disease levels well below 100%, there is no need to adjust the models for approaching the upper limit, and we can use the simple linear and exponential models to plan strategies:
39Examining these models, we can see that in both there are three ways in which we can reduce x at any point in the epidemic:Reduce the initial inoculum (Q in the monocyclic model and xo in the polycyclic model). (Actually xo is the initial incidence of disease, which is proportional to the initial inoculum.)Reduce the rate of infection (R in the monocyclic model and r in the polycyclic model)Reduce the duration of the epidemic (the time, t, at the end of the epidemic)
40These can be used as three major strategies for managing plant disease epidemics, and we can organize our plant disease control tactics under one or more of these overall strategies.Furthermore, by means of the model we can assess the quantitative impact of each strategy, not only by itself, but in its interaction with others.
41The monocyclic modelIt is clear from the above model of a monocyclic epidemic that Q, R, and t have equal weight in their effect on x. A reduction in the initial inoculum or the rate of infection will result in a reduction in the level of disease by the same proportion at any time, t, throughout the epidemic. If t can be reduced (for example, by shortening the season), disease will be reduced proportionately.
42The polycyclic modelIf r is very high, the apparenteffect of reducing xo is to delaythe epidemic.If r is very high, xo must be reduced to very low levels to have a significant effect on the epidemic.Reducing r has a relatively greater effect on the epidemic than reducing xo.Reducing xo makes good strategic sense only if r is low or if r is also being reduced.
43The Traditional Principles Revisited To make the conceptual leap from disease control to disease management, the traditional principles can be modified by fitting them as tactics within each of the three major disease management strategies and by slightly changing the wording to reflect the quantitative impact of the action rather than an absolute effect:
44PRINSIP PENGELOLAAN PENYAKIT TUMBUHAN Pada prinsipnya, untuk mengelola penyakit tumbuhan ada strategi dan ada taktik yang dapat digunakan.Taktik dipakai untuk mencapai tujuan berdasar strategi yang dicanangkan.Secara umum, ada tiga strategi yang dapat dilakukan untuk pengendalian penyakit tumbuhan yaitu :(1) strategi untuk mengurangi inokulum awal,(2) strategi untuk mengurangi laju infeksi, dan(3) strategi untuk mengurangi lamanya epidemi.Sedangkan taktik pada prinsipnya ada enam, yaitu avoidan, ekslusi, eradikasi, proteksi, resistensi, dan terapi.
45Tactics for the Reduction of Initial Inoculum Avoidance—reduce the level of disease by selecting a season or a site where the amount of inoculum is low or where the environment is unfavorable for infectionExclusion—reduce the amount of initial inoculum introduced from outside sourcesEradication—reduce the production of initial inoculum by destroying or inactivating the sources of initial inoculum (sanitation, removal of reservoirs of inoculum, removal of alternate hosts, etc.)Protection—reduce the level of initial infection by means of a toxicant or other barrier to infectionResistance—use cultivars that are resistant to infection, particularly the initial infectionTherapy—use thermotherapy, chemotherapy and/or meristem culture to produce certified seed or vegetative planting stock
46Tactics for the Reduction of the Infection Rate Avoidance—reduce the rate of production of inoculum, the rate of infection, or the rate of development of the pathogen by selecting a season or a site where the environment is not favorableExclusion—reduce the introduction of inoculum from external sources during the course of the epidemicEradication—reduce the rate of inoculum production during the course of the epidemic by destroying or inactivating the sources of inoculum (roguing)Protection—reduce the rate of infection by means of a toxicant or some other barrier to infectionResistance—plant cultivars that can reduce the rate of inoculum production, the rate of infection, or the rate of pathogen developmentTherapy—cure the plants that are already infected or reduce their production of inoculum
47Tactics for the Reduction of the Duration of the Epidemic Avoidance—plant early maturing cultivars or plant at a time that favors rapid maturation of the cropExclusion—delay the introduction of inoculum from external sources by means of plant quarantine
48PENGENDALIAN PENYAKIT TUMBUHAN MENGURANGI LAJU INFEKSIMENGURANGI LAMANYA EPIDEMIMENGURANGI INOKULUM AWALPENGENDALIAN PENYAKIT TUMBUHANEKSLUSIAVOIDANSTRATEGIWaktu tanam, lahan, lingkungan yg tak cocok untuk patogenMengurangi jumlah inokulum awal yang berasal dari luar lahanSanitasi, buang sumber inokulum, musnahkan inang antara, dsb.Aplikasi fungisida, atau buat penghalang infeksi pd tanamanKultivar yang tahan terhadap infeksi inokulum awalTerapi panas, kimia, benih / bag. tan. vegetativ bebas penyakitTERAPIERADIKASIRESISTENPROTEKSITAKTIKLaju dikurangi dg waktu tanam, lahan, lingkungan yg tak cocokKurangi masuknya inokulum selama terjadinya epidemiTebang, pangkas, musnahkan inokulum saat terjadinya epidemiKurangi laju infeksi dengan fungisida atau penghalang lainKultivar yang mengurangi laju in-feksi/perkemb.patogen/inokulumSembuhkan tanaman yang telah terinfeksiTanaman cepat dewasa agar terhindar dari infeksiHambat introduksi inokulum dari luar dengan karantina
49Peranan pengendalian penyakit tumbuhan Ditujukan untuk mencegah atau mengurangi terjadinya penyakit sehingga tanaman dapat memberikan hasil yang menguntungkan.Usaha ini biasanya ditujukan terhadap tanaman sebagai populasi dan tidak terhadap tanaman sebagai individu.Kebanyakan dari usaha pengendalian penyakit memerlukan perpaduan dari berbagai cara.
50Cara pendekatan pendekatan terhadap tanaman pendekatan yang ditujukan terhadap penyebab penyakit tertentuTerintegrasi ke dalamMETODA PENGENDALIAN
51Penghindaran patogen Pemilihan daerah pertanian. Pemilihan waktu tanam.Penggunaan benih yang bebas penyakit.
52Eksklusi patogen Perawatan bahan tanaman. Karantina tumbuhan. Pembasmian serangga vektor.
53Eradikasi patogen Pergiliran tanam. Membuang atau menghancurkan tanaman atau bagian tanaman yang terserang.Perlakuan tanah.
54Perlindungan tanaman Pengendalian serangga pembawa patogen. Mengubah keadaan lingkungan.Mengubah keadaan zat hara.
55Mengembangkan tanaman yang resisten Resistensi fisiologisResistensi mekanisResistensi fungsionalResistensi oleh Khemoterapi
56a. Resistensi fisiologis yang biasanya didasarkan kepada adanya zat di dalam protoplasma yang menghambat infeksi patogen dan perkembangannya lebih lanjut di dalam tanaman.b. Resistensi mekanis yang berhubungan dengan struktur atau morfologi dari bagian-bagian tanaman tertentu meliputi sifat karakteristik yang dipunyai oleh tanaman yang menyulitkan patogen mengadakan kontak secara langsung dengan bagian yang akan diinfeksinya seperti adanya lapisan kutikula atau lapisan gabus yang tebal.
57c. Resistensi fungsional yang berhubungan dengan waktu penutupan stomata. d. Resistensi oleh Khemoterapi dimana terdapat kemungkinan mengubah ketahanan terhadap patogen yang terdapat dalam protoplasma dengan pemberian senyawa kimia pada tanaman. Pada umumnya cara tersebut memperlambat atau mengurangi timbulnya penyakit.
58Terapi yang diberikan kepada tanaman sakit Khemoterapi.Perlakuan panas.Menghilangkan bagian tanaman yang kena infeksi.
62Cultural controlMengusahakan tanaman terhindar dari kontak dengan patogen, mengusahakan kondisi lingkungan tidak menguntungkan bagi patogen dan melenyapkan atau mengurangi jumlah patogen pada suatu tanaman, lahan atau wilayah
63Biological controlMeningkatkan resistensi inang atau menciptakan kondisi yang menguntungkan bagi mikroorganisma antagonistik bagi patogen
64Physical and chemical control Melindungi tanaman dari inokulum patogen yang sudah ada atau akan ada, atau mengobati suatu infeksi yang sudah/sedang berlangsung
65Cultural control Regulatory control Biological control MENGURANGI LAJU INFEKSIMENGURANGI LAMANYA EPIDEMIMENGURANGI INOKULUM AWALPENGENDALIAN PENYAKIT TUMBUHANEKSLUSIAVOIDANSTRATEGITERAPIERADIKASIRESISTENPROTEKSITAKTIKRegulatory controlBiological controlCultural controlPhysical and chemical control
66PENGENDALIAN PENYAKIT TUMBUHAN SECARA KIMIAWI pestisida
67PERATURAN PEMERINTAH NO. 7 TAHUN 1973 Untuk melindungi keselamatan manusia dan sumber-sumber kekayaan alam khususnya kekayaan alam hayati, dan supaya pestisida dapat digunakan efektif, maka peredaran, penyimpanan dan penggunaan pestisida diatur dengan Peraturan Pemerintah No. 7 Tahun Dalam peraturan tersebut antara lain ditentukan bahwa:
68tiap pestisida harus didaftarkan kepada Menteri Pertanian melalui Komisi Pestisida untuk dimintakan izin penggunaannyahanya pestisida yang penggunaannya terdaftar dan atau diizinkan oleh Menteri Pertanian boleh disimpan, diedarkan dan digunakanpestisida yang penggunaannya terdaftar dan atau diizinkan oleh Menteri Pertanian hanya boleh disimpan, diedarkan dan digunakan menurut ketentuan-ketentuan yang ditetapkan dalam izin pestisida itutiap pestisida harus diberi label dalam bahasa Indonesia yang berisi keterangan-keterangan yang dimaksud dalam surat Keputusan Menteri Pertanian No. 429/ Kpts/Mm/1/1973 dan sesuai dengan ketentuan-ketentuan yang ditetapkan dalam pendaftaran dan izin masing-masing pestisida.
69What is a fungicide?Fungicides are pesticides that specifically kill fungi or inhibit fungal developmentAbout 40 different classes of fungicides used for plant protectionClasses are based on target site and biochemical mode of action
71Systemicity Non-systemic Systemic Do not penetrate into plant Redistribute on plant surfacesMulti-site inhibitorsKills spores/inhibits germinationProtectant onlyBroad spectrumPenetrate into plantRedistribute on & within plantsSingle-site inhibitorsInhibits spore germination and or mycelial growthProtectant and curativeSelective
72Non-systemics Mimimal redistribution from the point of deposition Works by contact with the fungusAdequate coverage is essentialOn the cuticleRedistributed washed off by waterEBDCs, Chlorothalanil, etc.
73Systemics Local Systemic Local redistribution from the point of depositionOn the cuticleThrough the leaf (translaminar)Extent is variable
74Systemics Limited systemic (acropetal penetrant) Good movement from the point of applicationThrough tissuesInside the vasculatureBulk movementDMIs, Phenylamides
75Systemics True Systemics (Basipetal penetrant) Only one fungcide Fosetyl-AlMoves through plantDown into rootsGood against soil-borne oomycetes
76Single Site v. Multi-site Systemic v. non-Systemic Non-systemic/Multi-SiteSystemic/Single SiteProtectant onlyCan wash offShorter application intervalsBroad spectrumLow Risk of ResistanceProtectant and curativeLess prone to washing offLonger application intervalsSelectiveHigh Risk of Resistance
77Pola Laku Kimiawi pada Pengendalian Penyakit Tanaman Biological mode of action Aksi Fungisida dapat diekspresikan melalui salah satu dari dua cara ekspresi fisikPenghambatan perkecambahanspora.Penghambatan pertmbuhan jamur.
78Physiological mode of action Apa yang terjadi pada tingkatan seluler shg dapat menyebabkan pengaruh visibel pada perkecambahan spora dan pertumbuhan jamur?
79Mengapa perlu mengenali pola laku fungisida secara fisiologis? For resistance managementand preservation of fungicide effectiveness.UntreatedTreated
80The physiological mode of action Fungicides are metabolic inhibitors and their modes of action can be classified into four broad groups.Inhibitors of electron transport chain.Inhibitors of enzymes.Inhibitors of nucleic acid metabolism and protein synthesis.Inhibitors of sterol synthesis.
81A typical cell and cell components Electron transport chainEnzymesNucleic acid metabolismand protein synthesisSterol synthesis
82Inhibition of electron transport chain (Respiration in mitochondria) SulfurDisrupts electron transport along the cytochromesStrobilurins (azoxystrobin, kresoxim-methyl, pyraclostrobin, trifloxystrobin)Inhibit mitochondrial respiration, blocking the cytochrome bc1 complex.
83Discovery and Synthesis from Natural Products Strobilurus tenacellusMyxococcus fulvusOudemansiella mucida
84Synthesis from Natural Products Strobilurin AOOudemansin AEnol ether stilbeneCNONONEnol Ether GroupOxime Ether Group
85Inhibition of enzymes Copper Nonspecific denaturation of proteins and enzymes.Dithiocarbamates (maneb, manzate, dithane, etc)Inactivate –SH groups in amino acids, proteins and enzymes.Substituted aromatics (chlorothalonil, PCNB)Inactivate amino acids, proteins and enzymes by combining with amino and thiol groups.Organophosphonate (fosetyl-Al)Disrupts amino acid metabolism.
86Inhibition of nucleic acid metabolism and protein synthesis Benzimidazoles (thiophanate-methyl)Inhibit DNA synthesis (nuclear division).Phenylamides (mefenoxam)Inhibits RNA synthesis.Dicarboximides (iprodione, vinclozolin)Inhibits DNA and RNA synthesis, cell division and cellular metabolism.
87Inhibition of sterol synthesis (Inhibit demethylation of ergosterol) Ergosterol is the major sterol in most fungi.It is essential for membrane structure and function.
88Sterol inhibiting fungicides Imidazoles (imazalil)Triazoles (propiconazole, myclobutanil, tebuconazole, triflumazole)Morpholines (dimethomorph)Inhibits sterol production at different site than imidazoles and triazoles. Affects cell wall production.
89Biological control of plant pathogens Christine Roath
90Overview What is biological control, what are the benefits to its use Mechanism of biological controlRequirements of successful biocontrolWorking example of biocontrol
91What is biological control? First coined by Harry Smith in relation to the biological control of insectsSuppression of insect populations by native or introduced enemiesGeneric termsA population-leveling process in which the population of one species lowers the number of another
92Why use biological control? WHEN :Biological control agents areExpensiveLabor intensiveHost specificWHILE :Chemical pesticides are:cost-effectiveeasy to applyBroad spectrum
93Why use biological control? WILL:Chemical pesticidesImplicated in ecological, environmental, and human health problemsRequire yearly treatmentsBroad spectrumToxic to both beneficial and pathogenic speciesBUT:Biological control agentsNon-toxic to humanNot a water contaminant concernOnce colonized may last for yearsHost specificOnly effect one or few species
94Mechanisms of biological control of plant pathogens Antibiosis – inhibition of one organism by another as a result of diffusion of an antibioticAntibiotic production common in soil-dwelling bacteria and fungiExample: zwittermicin A production by B. cereus against Phytophthora root rot in alfalfa
95Mechanisms of biological control of plant pathogens Nutrient competition – competition between microorganisms for carbon, nitrogen, O2, iron, and other nutrientsMost common way organisms limit growth of othersExampleP. fluorescens, VITCUS, prevents bacterial blotch by competing with P. tolaasii
96Mechanisms of biological control of plant pathogens Destructive mycoparasitism – the parasitism of one fungus by anotherDirect contactCell wall degrading enzymesSome produce antibioticsExampleTrichoderma harzianum, BioTrek, used as seed treatment against pathogenic fungus
97Requirements of successful biocontrol Highly effective biocontrol strain must be obtained or producedBe able to compete and persistBe able to colonize and proliferateBe non-pathogenic to host plant and environment
98Requirements of successful biocontrol Inexpensive production and formulation of agent must be developedProduction must result in biomass with excellent shelf liveTo be successful as agricultural agent must beInexpensiveAble to produce in large quantitiesMaintain viability
99Requirements of successful biocontrol Delivery and application must permit full expression of the agentMust ensure agents will grow and achieve their purposeCoiling of Trichoderma around a pathogen. (Plant Biocontrol by Trichoderma spp. Ilan Chet, Ada Viterbo and Yariv Brotman)
100Plant pathogen control by Trichoderma spp. Trichoderma spp. are present in nearly all agricultural soilsAntifungal abilities have been known since 1930sMycoparasitismNutrient competitionAgriculturally used as biocontrol agent and as a plant growth promoter
101Plant pathogen control by Trichoderma spp. How is it applied?Favored by presence of high levels of plant rootsSome are highly rhizosphere competentCapable of colonizing the expanding root surfaceCan be used as soil or seed treatment
102Plant pathogen control by Trichoderma spp. Action against pathogenic fungiAttachment to the host hyphae by coilingLectin-carbohydrate interaction(Hubbard et al., Phytopathology 73: ).
103Plant pathogen control by Trichoderma spp. Action against pathogenic fungi2. Penetrate the host cell walls by secreting lytic enzymesChitinasesProteasesGlucanases(Ilan Chet, Hebrew University of Jerusalem).
104Plant pathogen control by Trichoderma spp. Some strains colonize the root with mycoparasitic propertiesPenetrate the root tissueInduce metabolic changes which induce resistanceAccumulation of antimicrobial compounds
105Plant pathogen control by Trichoderma spp. Commercial availabilityT-22Seed coating, seed pieces, transplant starterProtects roots from diseases caused by Pythium, Rhizoctonia and FusariumInteracts with the Rhizosphere, near the root hairs and increases the available form of nutrients needed by plants.
106Plant pathogen control by Trichoderma spp. Future developmentsTransgenesBiocontrol microbes contain a large number of genes which allow biocontrol to occurCloned several genes from Trichoderma as transgenesProduce crops which are resistant to plant diseasesCurrently not commercially available
107SUSTAINABLE MANAGEMENT OF SOIL-BORNE PLANT DISEASES
108a reduction of biodiversity of soil organisms Soil-borne diseases Restoring beneficial organisms that attack, repel, or otherwise antagonize disease-causing pathogens will render a soil disease-suppressivePlants growing in disease-suppressive soil resist diseases much better than in soils low in biological diversity.Beneficial organisms can be added directly, or the soil environment can be made more favorable for them through use of compost and other organic amendments.Compost quality determines its effectiveness at suppressing soil-borne plant diseases.
109Why Disease?Plant diseases result when a susceptible host and a disease-causing pathogen meet in a favorable environmentIf any one of these three conditions were not met, there would be no disease.
110Many intervention practices (fungicides, methyl bromide fumigants, etc Many intervention practices (fungicides, methyl bromide fumigants, etc.) focus on taking out the pathogen after its effects become apparent.How to emphasizes on making the environment less disease-favorable and the host plant less susceptible.