PENGEDALIAN PENYAKIT TUMBUHAN

1. PENGEDALIAN PENYAKIT TUMBUHAN Aris Mumpuni

2. Disease Progress Disease 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.

3. Disease Progress When 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.

4. Disease Progress For 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)

5. Phytophthora blight of pepper seedlings

6. Fusarium kernel rot of maize

7. Disease Progress On 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.

8. Bean rust

9. Grey leafspot of maize

10. Disease Progress Obviously 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.

11. Sclerotium rolfsii on beans

12. Black shank on tobacco

13. Disease Progress Likewise, 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).

14. Black stem rust on ryegrass

15. Net blotch on barley

16. To 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.

17. The 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.

18. what kinds of diseases lead to linear disease progress and what factors affect the slope of the line (the rate of disease progress). 2. 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. 3. why epidemics sometimes level off and what imposes limits to their development. We have to know :

19. The 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.

20. The 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.

21. The 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.

22. Pathogens 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.

23. Generally 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".

24. Epidemic: "Change in disease intensity in ahostpopulation over time and space.“

25. Change : often increase -- a dynamic process Disease : dealing with diseases, not just the pathogen (or plant/crop) Host : Organism infected (or potentially infected) by another organism Population : a population phenomenon Time and space : two physical dimensionsof interest.

26. Epidemiology: • • 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 are responsible for, or contribute to, epidemic occurrence. • • The science of populations of pathogens in populations of host plants, and the diseases resulting therefrom under the influence of the environment and human interferences.

28. All 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.

29. Since 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.

30. From 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.

31. 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.

32. 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. Traditional Principles of Plant Disease Control

33. While 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.

34. A 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.)

35. Furthermore, 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.

36. Finally, 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.

37. The 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.)

38. The 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:

39. Examining 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)

40. These 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.

41. The monocyclic model It 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.

42. The polycyclic model • If r is very high, the apparent effect of reducing xo is to delay the 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.

43. The 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:

44. PRINSIP 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.

45. Tactics 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 infection • Exclusion—reduce the amount of initial inoculum introduced from outside sources • Eradication—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 infection • Resistance—use cultivars that are resistant to infection, particularly the initial infection • Therapy—use thermotherapy, chemotherapy and/or meristem culture to produce certified seed or vegetative planting stock

46. Tactics 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 favorable • Exclusion—reduce the introduction of inoculum from external sources during the course of the epidemic • Eradication—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 infection • Resistance—plant cultivars that can reduce the rate of inoculum production, the rate of infection, or the rate of pathogen development • Therapy—cure the plants that are already infected or reduce their production of inoculum

47. Tactics 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 crop • Exclusion—delay the introduction of inoculum from external sources by means of plant quarantine

48. PENGENDALIAN PENYAKIT TUMBUHAN STRATEGI TAKTIK AVOIDAN Waktu tanam, lahan, lingkungan yg tak cocok untuk patogen EKSLUSI Mengurangi jumlah inokulum awal yang berasal dari luar lahan ERADIKASI Sanitasi, buang sumber inokulum, musnahkan inang antara, dsb. MENGURANGI INOKULUM AWAL PROTEKSI Aplikasi fungisida, atau buat penghalang infeksi pd tanaman RESISTEN Kultivar yang tahan terhadap infeksi inokulum awal TERAPI Terapi panas, kimia, benih / bag. tan. vegetativ bebas penyakit AVOIDAN Laju dikurangi dg waktu tanam, lahan, lingkungan yg tak cocok EKSLUSI Kurangi masuknya inokulum selama terjadinya epidemi ERADIKASI Tebang, pangkas, musnahkan inokulum saat terjadinya epidemi MENGURANGI LAJU INFEKSI PROTEKSI Kurangi laju infeksi dengan fungisida atau penghalang lain RESISTEN Kultivar yang mengurangi laju in-feksi/perkemb.patogen/inokulum TERAPI Sembuhkan tanaman yang telah terinfeksi AVOIDAN Tanaman cepat dewasa agar terhindar dari infeksi MENGURANGI LAMANYA EPIDEMI EKSLUSI Hambat introduksi inokulum dari luar dengan karantina

49. Peranan 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.

50. Cara pendekatan • pendekatan terhadap tanaman • pendekatan yang ditujukan terhadap penyebab penyakit tertentu Terintegrasi ke dalam METODA PENGENDALIAN