Master Gardener training in PLANT PATHOLOGY supplemental

Transcription

1 PLPA MG1 rev Kevin Ong, PhD Associate Professor & Extension Specialist Dept. of Plant Pathology & Microbiology Director Texas Plant Disease Diagnostic Lab Master Gardener training in PLANT PATHOLOGY supplemental The following packet is a set of supplementary information to be added to your Master Gardener handbook to enhance the information contained in it. In general, the MG plant pathology training will cover the following material in a full-day training session (6 hours): Unit 1: Basic concepts in plant pathology What, why, when and how disease happens Utility of understanding basic disease concepts Unit 2: Overview survey of plant pathogens Emphasis on biotic pathogens Unit 3: General principles of managing disease problems Management strategies categorized by principles Unit 4: Basic of field/on-site plant problem diagnosis Skills identification and training for on-site diagnosis Abbreviated training sessions (3-4 hours) will cover shortened versions of units 1,2 and 3. Slide sets for the trainings will be made available on the Master Gardener Training Resources page on the plantclinic website (/mastergardener ) Please understand that in-depth understanding of plant pathology CANNOT be achieved in a short oneday training. This session aims to expose Master Gardener interns to the vast area of scientific curiosity called plant pathology, and to provide some resource for the intern to continue the learning process. If you find additional resources on the internet and are concerned about reliability of information, you can contact me via at kevo@tamu.edu (use subject header: MG-info question ) I would also encourage you to share any information that you find interesting with your fellow Master Gardeners and Extension county agents. Always remember that: PLANT PATHOLOGY is the study of plant disease aka study of the things that can kill or make a plant sick.

2 PLPA MG2 Master Gardener Training supplemental Some Principles of Plant Pathology The following are useful concepts in the field of plant pathology. They are limited to generalizations which apply to many or all groups of diseases. A. Etiology (cause) 1. Disease results from the continued irritation of plant by a living or nonliving agent. 2. Effects of microorganisms on higher plants are modified by environment. 3. Fungi are the major microorganisms responsible for disease. 4. The diagnosis of disease is based primarily on signs and symptoms. 5. Each species of plant is subject to its characteristic diseases. 6. Most diseases of economic plants have already been correctly diagnosed. 7. Unfavorable environments and genetic constitutions may cause nonparasitic disease. 8. Resistance to a specific disease is more common than susceptibility. 9. Species of pathogens exist in many physiological forms. 10. Pathogens commonly adapt themselves to resistant plant varieties. 11. The closer the genetic relation between hosts, the more similar (or closely related) their pathogens. B. Importance Several pathogens have the potential to destroy any crop but rarely do so. 13. Diseases reduce yield and quality of crop. 14. Diseases increase the variability and cost of crop production. C. Symptomology 15. Symptoms of disease are characteristic for different causal agents. 16. Some infections cause no recognized symptoms. 17. Parasites may increase the local or general growth of their host. 18. Infections and injuries increase plant respiration and permeability. 19. Fungi, bacteria, and nematodes usually cause localized infections. Viruses usually cause systemic infections. 20. Symptoms may be systemic, even if the pathogen is localized. Master Gardener Training (ONG) Some Principles of Plant Pathology Page 1 of 2

3 Master Gardener Training (ONG) Some Principles of Plant Pathology Page 2 of 2 D. Life History 21. The dormant stage of pathogens is more resistant to environment than the active stage. 22. Some pathogens have cycles requiring an alternate host. 23. Most pathogens can be cultured on nonliving substrata. 24. Most fungi and nematodes enter the plant actively, whereas bacteria and viruses enter passively. 25. The dispersal of pathogens is usually passive, but may be active and may be aided by vectors. 26. Principle vectors or pathogens are wind, water, arthropods, and man. 27. Specific pathogens enter through specific sites and colonize specific tissues. 28. Soil and plant debris are major reservoirs of plant pathogens. 29. Systemic infections increase at a slower rate than local infections. E. Predisposition 30. Resistance to a specific pathogen is more common than susceptibility. 31. Plants may increase or decrease in susceptibility with age. 32. High nitrogen fertilization commonly favors disease whereas, high potassium fertilization commonly reduces disease. 33. Several minor nutrients may be decisive for specific disease situations. F. Epidemiology 34. Pathogens increase more rapidly in pure stands than in mixed stands of plants or with rotation of crops. 35. Most fungi and bacteria require free moisture for the initiation of infection. 36. Major sources of free water are rain, dew, guttation water, and irrigation water. 37. The optimum temperature for most diseases is about 25 C(77 F). 38. Alternating light and darkness are usually necessary for normal disease development. 39. The effect of the environment is most critical during penetration of the plant. 40. Pathogens are typically more tolerant of extremes in heat or cold than are the plant host. G. Control 41. All knowledge of factors affecting disease has potential value in control. 42. Control of disease is usually directed at inhibition of the pathogen. 43. Control practices may be classified under exclusion, eradication, protection, immunization, and therapy. 44. Treatments which are therapeutic to one pathogen may predispose to another. 45. Protective measures become less effective with increasing inoculum potenti The information given herein is for educational purposes only. References to commercial products or trade names are made with the understanding that no discrimination is intended and no endorsement by Texas A&M AgriLife Extension Service personnel is implied. Educational programs of the Texas A&M AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin. The Texas A&M University System, U.S. Department of Agriculture, and the County Commissioners Courts of Texas Cooperating

4 PLPA MG3 SUPPLEMENTAL GLOSSARY OF PLANT PATHOLOGY TERMS Adapted from several sources (including Plant Pathology 4 th Ed. GN Agrios) Abiotic disease: A disease caused by a nonliving factor (i.e., hail, cold, nutrient, etc.) Anthracnose: A necrotic and sunken ulcer-like lesion on the stem, leaf, fruit, or flower of the host plant caused by a fungus. Biotic disease: A disease caused by a living organism (i.e., fungus, virus, etc.) Blight: General and extremely rapid browning of leaves, branches, twigs, and floral organs resulting in their death. Usually young growing tissues are affected. Canker: Generally a dry, discolored, sunken, or cracked area on a stem, branch, or trunk. A canker generally has a distinct border between diseased and healthy tissue whereas a rot does not. Cankers may be caused by pathogens or by injuries. Chlorosis: Yellowing or whitening of normally green leaves. May be due to a virus, nutrient deficiency, lack or oxygen in a waterlogged soil, alkaline soil, or other factors. Damping off: The rapid death and collapse of very young seedlings in the greenhouse or field. Common damping-off pathogens include the fungi Pythium, Rhizoctonia, Fusarium, and Phytophthora. Decline: Poor growth of plants; leaves small, brittle, yellowish, or red; some defoliation and dieback commonly is present. Dieback: Extensive death of twigs beginning at the tips and advancing toward the bases. Dry rot: Disintegration of fruits, tubers, roots, or stems by fungis without release of liquids (see soft rot). Enation: Malformation or overgrowth of leaves, petioles, or flowers, induced by certain viruses. Host range: The various kinds of plants that may be attacked by a parasite. Hypha (pl.= hyphae): Thread-like structure that constitutes the body (mycelium) of a fungus. Leaf spot: Discrete lesions on host leaves consisting of dead and collapsed cells. Master Gardener Training (ONG) Glossary supplemental Page 1 of 2

5 Master Gardener Training (ONG) Glossary supplemental Page 2 of 2 Mollicute: Bacterium without a cell wall. This group includes phytoplasmas and spiroplasmas which infect the phloem (food-conducting tubes) of plants. Mosaic: Leaf symptoms characterized by intermingled patches of normal and light green or yellowish color; generally viral. Mycelium (pl. = mycelia): A mass of hyphae that make up the body of a fungus. Necrosis: Death of plant parts which generally turn black or brown. Parasite: An organism living on or in another living organism (host) and obtaining its food from the latter. Obligate: Requires a living host (eg. Viruses, rust fungi, mildew fungi, plant parasitic nematodes) Non-obligate: can live on host or non-living material (eg. Most bacteria and fungi) Pathogen: An organism or agent (e.g., fungus, bacterium, nematode, virus, or viroid) capable of causing disease in a particular host or range of hosts. Pathogenesis: The sequence of processes in disease development from the time of infection to the final reaction in the host. Race: A genetically- and often geographically-distinct mating group within a pathogenic species. Ringspot: A circular area of chlorosis or necrosis with a green center; generally viral. Root rot: Decay of roots in a living plant; often caused by pathogenic fungi. Scab: Localized lesions on host fruit, leaves, tubers, etc., usually slightly raised or sunken and cracked, giving a scabby appearance. Sign: The appearance or evidence of the pathogen. Soft rot: Slimy softening and decay of fruits, roots, bulbs, tubers, and fleshy leaves; caused by fungi or bacteria (see dry rot). Symptom: The appearance of disease or injury. Witches' broom: Broom-like growth or massed proliferation caused by the dense clustering of branches of woody plants; caused by false mistletoes, fungi (rusts and Taphrinales), phytoplasmas, bacteria, viruses, and nematodes. Yellows: A plant disease characterized by yellowing and stunting of the host plant. The information given herein is for educational purposes only. References to commercial products or trade names are made with the understanding that no discrimination is intended and no endorsement by Texas A&M AgriLife Extension Service personnel is implied. Educational programs of the Texas A&M AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin. The Texas A&M University System, U.S. Department of Agriculture, and the County Commissioners Courts of Texas Cooperating

6 PLPA MG4 A. Does a plant problem exist? Master Gardener Training SUPPLEMENTAL Using a Plant Problem Diagnostic Key* Identify and inspect plant area surrounding plant community. Are plant characteristics normal for this species/cultivar at the current time of year and age of plant? 1. Abnormal - go to B 2. Normal B. Check for patterns and determine time frame for damage. Collect information and ask questions. Patterns of damage and time frame for damage are important clues for distinguishing between biotic and abiotic factors. B.1. Nonuniform damage; damage progressive over time. Go to C.1. Nonuniform plant injury occurring on one or several plants. Damage over time is progressive on plant, spreading to other similar plants and across the area. These indicate a biotic agent. B.2. Uniform damage; single event in time. Go to C.2. Uniform plant damage on either individual plants or over a designated area. Damage event occurs, but does not spread over time to other parts or inj ured plants. Patterns may vary depending on the cause. Usually clear distinction between injured and non-injured tissue. These factors indicate an abiotic agent. B.3. Several symptom patterns indicating complex problem. Go to C.3. Different patterns of distribution of symptoms within a planting suggest multiple and/or synergistic causal factors or events. C. Refine the diagnosis C.1. Distinguish between biotic agents. a. Signs and symptoms of pathogens. i. Fungi ii. Bacteria iii. Viruses iv. Nematodes v. Others - phytoplasmas, parasitic plants b. Signs and symptoms of other pests. i. Mites ii. Insects iii. Other animals C.2. Distinguish between abiotic agents. Master Gardener Training (ONG) Diagnostic Key Example Page 1 of 2

7 Master Gardener Training (ONG) Diagnostic Key Example Page 2 of 2 a. Look for signs of mechanical damage such as broken stems, crushed plants, girdling from plant ties, etc. b. Check for changes in environmental conditions or extreme environmental events i. Water stress ii. Temperature extremes iii. Windburn & sunburn iv. Lightning & hail injury v. Light intensity & quality c. Check for chemical agents. Where does the damage occur? Observe pattern on individual plants. Analyze damage patterns across the area (greenhouse, yard, field, natural area). What are these patterns showing you about the source and/or delivery methods? i.e. How did the chemical get there? i. Nutritional disorders ii. Phytotoxicity from pesticides, pollutants, or poor water quality. C.3. Complex etiology - possible contributing factors: a. Genetic abnormalities b. Soil factors c. Exopathogens - microorganisms that live outside plants and induce disease by secreting phytotoxic substances that the plants absorb. d. latrogenic problems - diseases which are increased in their severity or are the result of the use of agrichemicals or pesticides. The use of soil-applied herbicides often compound non-target seedling diseases from pathogens such as pythium, phytophthora, rhizoctonia, or fusarium. e. Predisposing factors f. Other unknown factors D. Consult references, submit sample for laboratory diagnosis. Assistance may be needed for identifying the specific responsible factor(s). Know which reference books to consult, what specialists to contact and what type of sample to collect. E. Synthesis of information and subsequent ranking of probable causes of the problem. * Modified from Assessing Plant Problems in Cropping Systems: A Systematic Approach, Fla. Dept. Agric. & Consumer Services Plant Pathology Circular No Compiled by Dr. Janell Stevens Johnk. Former Extension Plant Pathologist, Texas A&M at Dallas(January20, 1998). The information given herein is for educational purposes only. References to commercial products or trade names are made with the understanding that no discrimination is intended and no endorsement by Texas A&M AgriLife Extension Service personnel is implied. Educational programs of the Texas A&M AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin. The Texas A&M University System, U.S. Department of Agriculture, and the County Commissioners Courts of Texas Cooperating

8 PLPA MG5 The logical steps in evaluating plant problems. Plant is exhibiting ABNORMAL symptoms. EVALUATE INQUIRY or PROBLEM Is the problem(s) described or observed on the plant due to normal plant development for that particular time of the year? YES There is a likelihood of NO DISEASE PROBLEM INSECT PROBLEM Refer to an entomologist. YES NO YES Are there insects observed on the plant? Is the damage consistent with probable insect attack? NOTE: Presence of insects does not always mean that insects are the root cause of a plant problem NO Probably NOT insect problem. Are there signs of the pathogen(s) on damaged areas? NO Pathogen(s) not observed. IDENTIFY type of pathogen (fungi, bacteria, nematode) Is damage observed consistent pathogen attack? YES NO YES YES PROBABLY BIOTIC AGENT ENLIST help of the Texas Plant Disease Diagnostic Laboratory or the area plant pathologist. Is it or can it be identified? NO Is the damage scattered and is not uniformly distributed throughout tree and stand? YES NO NO PROBABLY ABIOTIC AGENT Abiotic problems are difficult to diagnose. Observed for obvious problems such as soil compaction, inadaptability of host, root disturbance. Obtain clues by understanding local environment conditions and query homeowner on tree management practices. Can problem be identified? PROBLEM IDENTIFIED! Consult Plant Disease Handbook and/or other resources for possible remedies or solutions. UNKNOWN MALADY Prescribe general care to maintain health of plant. Disease Diagnostic flow chart Page 1 of 1

9 PLPA MG6 HELPFUL THOUGHTS TO CONSIDER WHEN DIAGNOSING PLANT PROBLEMS By Dr. Larry W. Barnes - retired Extension Plant Pathologist & Diagnostician Problem: Evaluate plant and consider where leaf spots are occurring. Usually, leaf spots resulting from fungi or bacteria occur on younger tissue or older tissue, but usually not on both younger and older at the same time. Control: Avoiding foliar wetting and timely application of fungicide or bactericide should help. Problem: Consider time factor when evaluating leaf spots. Most fungal and bacterial leaf spots require several days for their development and leaf spots of different ages are usually obvious, spots that occur overnight my be the result of spray damage or pollution injury. Control: There is no feasible control after these types of spots have occurred. Problem: When the root system fails to function properly in the uptake and translocation of moisture and nutrients to the leaf tissue, marginal leaf bum, progressive development of leaf chlorosis, tip dieback, and wilting are common above ground symptoms. While other causes are possible, when any of these symptoms are evident, always check the root system. A healthy, active, functional, root system should be white (or white when root bark is scraped from its surface), of firm texture, should have no odor or at least no sour odor, and the cortex should not pull off leaving root strings. Control: Planting in well-drained areas and avoiding root injury during planting help minimize root rots. Problem: When plants wilt, several causal possibilities exist. Frequently, wilting results simply from lack of water. Under conditions of high light intensity, abundant air movement, and high temperatures, transpirational water loss from leaves can be very high. Excessive fertilization can also be responsible, especially if wilt symptoms occur soon after fertilization. Control: Root rots or soils that stay saturated with water can both induce plant wilting. Root rots are usually fungal in nature and simply result in the destruction of the ability of a root system to absorb the necessary water to maintain a turgid plant. Poor drainage and excessively wet soil can result in plant wilting because plant roots must have oxygen to respire and absorb water. If the soil pore space stays full of water, insufficient oxygen reaches and roots, respiration decreases, water uptake by roots stops, and plants wilt. Saturated soils also create ideal conditions for fungal root rots to get started. Make sure that drainage is adequate, and that plants are adequately watered. Avoid over fertilization and water to excess at each watering to help dissolve accumulated salts and to leach them from the root zone. Master Gardener Training (ONG) Helpful Thoughts by Barnes Page 1 of 1

10 PLPA MG7 Root symptoms Master Gardener Training Material SUPPLEMENTAL DISEASE SYMPTOMS Quick reference list (From Martha Mikkelson, Plant Disease Diagnostician, Montana State University) Injury to the root system often includes yellowing, stunting, or wilting of above-ground parts. Wash off the roots when possible and look for the following: - Small discolored or dead areas (fungi). - General death of the feeder roots or the entire root system (fungi). - Discoloration of the vascular tissue in the crown and lower stem (fungi, such as Verticillium spp. and Fusarium spp., bacteria). -Galls on roots (crown gall (caused by bacterium Agrobacterium tumefaciens, fungal diseases such as club rot of cabbage, root knot nematodes) Symptoms on storage organs Storage organs include tubers, bulbs, and corms. Symptoms on these organs include: - Discolored or dead areas that go deep into storage organs (fungi, bacteria) - Dry rots (fungi). - Soft rots accompanied by strong, repulsive odors (bacterial pathogens, such as Erwinia spp.) (Frequently, bacterial soft rots move into tissue originally attacked by pathogenic fungi, making diagnosis of the original pathogen difficult.) - Scabby lesions on potato skins (bacteria such as common scab). - Galls on storage organs (fungi, nematodes). - Internal problems (several viruses or bacteria, such as ring rot of potato). Seedling diseases - Seedlings fail to emerge, or fall over and die (damping-off caused by fungi such as Rhizoctonia, Pythium, and Fusarium) - Dead areas on cotyledons or stems (fungi, bacteria). Master Gardener Training (ONG) Symptoms supplemental Page 1 of 2

11 Master Gardener Training (ONG) Symptoms supplemental Page 2 of 2 Leaf symptoms - Leaf discoloration or yellowing in localized or distinct patterns (viral). - Necrotic (dead) areas on leaves, often containing fruiting bodies (fungi) - Necrotic areas on leaves, often with water-soaked margins (bacterial) - Small rusty-red, brown or black spots and stripes (fruiting bodies of rusts and smut fungi) - Leaf distortion (elongated, dwarfed, thickened, etc.) (viral). - Leaf galls (fungi such as peach leaf curl and oak leaf blister, insects). - White, powdery substance on leaves (powdery or downy mildew). - Wilting (vascular wilt fungi, root rot pathogens, bacteria, drought). Stem, branch, and trunk disorders - Cankers and complete or partial death of woody stems or branches (fungi and bacteria) - Sticky ooze from trunks and branches (bacteria, mechanical injury, stress, boring insects, sapsuckers (birds)) - Large conks and bracket-like fruiting structures on trunks and branches (wood-rotting fungi) - Galls or swellings on lower trunk and/or branches (crown gall bacterium, white pine blister rust) - Witches' brooms or excessive branching (fungi, mistletoes, phytoplasmas). - Extreme distortion, enlargement, and flattening of stems or branches (physiological/genetic condition known as fasciation). Flower symptoms - Odd color changes (often in a mosaic pattern) and/or distortion (viruses). - Death of flower parts (fungi such as gray mold (Botrytis spp., bacteria) - Individual flowers or seeds converted into masses of black spores (corn smut). - Flowers that are green and smaller and more dense than normal (phytoplasma) Fruit symptoms - Fruit decays, rots, and superficial spotting or russetting (fungi). Important diagnostic symptoms include specific color of rotted tissue, firmness of the tissue, and signs such as spores or fruiting structures. - Discolorations and malformations (viruses). - Discrete spots on fruit or soft rots in storage (bacteria). The information given herein is for educational purposes only. References to commercial products or trade names are made with the understanding that no discrimination is intended and no endorsement by Texas A&M AgriLife Extension Service personnel is implied. Educational programs of the Texas A&M AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin. The Texas A&M University System, U.S. Department of Agriculture, and the County Commissioners Courts of Texas Cooperating

12 PLPA MG8 Characteristic of some foliar problems: MASTER GARDENER TRAINING SUPPLEMENTAL Master Gardener Training (ONG) Foliar problems supplemental Page 1 of 1

13 PLPA MG9 Master Gardener Training Reference Material RESOURCES SUPPLEMENTAL Plant Disease Diagnosis 1. Identifying the plant (not all inclusive) a. Sunset Western Garden Book. b. Landscape Plants for Texas and Environs, M. Arnold. c. Audubon Field guide to North American Trees, E. Little d. Shinners & Mahler's Illustrated Flora of North Central Texas George M. Diggs, Jr., Barney L. Lipscomb, Robert J. O'Kennon e. Horticulture Agent or other Master gardeners f. Extension Horticulturist 2. Define the Problem a. Gathering information i. Master Gardener handbook: 1. plant health history acquisition questions 2. disease diagnostic key ii. Observations 1. your senses record observation physically 3. Develop list of potential disease causing agent a. Disease diagnostic flow charts 4. Refine the diagnosis a. Gather known information on suspects i. Textbooks ii. Reliable websites iii. Plant Disease compendium 5. Getting additional help: Diagnostic confirmation a. Reference literature i. Master gardener handbook ii. Extension publications ( iii. Wescott s Plant Disease Handbook iv. Disease of Trees and Shrubs, Sinclair, Lyon and Johnson v. APS plant disease compendia vi. Ortho s Plant Problem Solver (only so-so) vii. Foliage Plant Disease: Diagnosis and Control, Chase. b. TX Plant Disease Diagnostic Laboratory website Master Gardener Training (ONG) Resource Supplemental Rev Page 1 of 1

14 PLPA MG10 Addendum: This document is a historical one showing the various LD50 value of some chemicals (conventional & natural). A smaller LD50 # means the product is more dangerous. This document is to illustrate that both conventional & natural products for pest/pathogen control are CHEMICALS! and should be treated and used with care & jurisprudence. - K.Ong Master Gardener Training (ONG) - Chemical LD50 eg. Page 1 of 1