Disease Management

1. Disease Management Terry Kirkpatrick, Plant Pathology M. Elena Garcia, Horticulture University of Arkansas

2. PlantDisease A malfunction of one or more plant systems due to continuous irritation that results in some symptom – Horsfall &Cowling, 1977

3. At least 90% of plant disease control is accomplished through proper cultural methods and sanitation. Unfortunately, modern agriculture sometimes ignores the fundamental concepts for convenience.

4. Types of Diseases • Biotic: result of infection of plant by a pathogen; able to spread to healthy plants • Types of pathogens: fungi, bacteria, viruses, nematodes, parasitic plants • Abiotic: result of environmental or cultural problem; cannot be transmitted • Types: light, temperature, hail, lightning, fire, wire girdling, pot-bound roots, air pollution, chemical injury, herbicide injury, nutrient deficiencies, chemical toxicity

5. Biotic Diseases • Fungi ------ ~80% • Bacteria ----- ~15% • Nematodes ----- <5% • Viruses ------ <5%

6. The Disease Triangle Disease development depends on: • Presence of pathogen (source of inoculum) • Host- Plant susceptibility • Environmental conditions must be favorable (light, moisture, temperature, soil fertility) PATHOGEN Total of virulence, abundance, etc. ENVIRONMENT Total of conditions favoring disease Amount of disease HOST Total of conditions favoring susceptibility

7. HOST Immune-no association other than coincidental causal entity (pathogen) has no effect. Susceptible – unable to suppress a pathogen; adverse response of plant to causal organism Resistant-ability to suppress the activity of a pathogen; may or may not have adverse effect on plant. Resistant Susceptible

8. Pathogen – an organism that is capable of causing disease Virulence – relative ability of the pathogen to cause disease Avirulence – inability of a pathogen to cause disease Avirulent Virulent In order for disease to occur, both a susceptible host and a virulent pathogen must be present

9. Host Environment Pathogen Environmental Manipulation You can’t control the weather…… But you can control the plant’s environment, at least to some degree

10. Environmental management for disease control • Irrigation: availability; quality; type • Site selection • Pruning; thinning; trellising; plant spacing; row spacing • Beds vs. flat planting • Annual vs. perennial (strawberry) • Mulching • Fertility; pH; overall plant nutrition balanced • Timely harvest

11. How do diseases Spread? • Soil-borne diseases • Wind-borne diseases • Seed-borne diseases • Vector-transmitted diseases

12. Soil-Borne Diseases • Introduced into soil • Inoculation • Wind • Infected seeds • Infected transplants • Other infected plants • Contaminated tools • Water • Crop residues provide an environment for pathogen • Can affect roots or any part of the plant • Smut, bacterial wilt, fusarium wilt, dampening-off

13. Wind-Borne Diseases • Spore transportation • May be great distances • Transport directly to aerial potions of plants • Inoculate soil • Rusts, powdery mildew, late and early blight of tomato, apple scab

14. Seed-Borne Diseases • Recommended to purchase certified disease-free seeds • Seed sterilization • Bacterial blights and anthracnose of peas • Potato ‘seeds’ • Viral diseases may spread by seeds

15. Vector-Transmitted Diseases • Insects • Carried from plant to plant on the mouth parts of insects • People • Pruning • Nematodes • Fungi

16. Epidemiology • 1. Single cyclic disease – most soilborne pathogens. Time

17. Epidemiology • 1. Multicyclic disease – Foliar pathogens stationary exponential lag Time Moisture on foliage is a primary factor.

18. Symptoms caused by fungi: • May be local or general • Necrotic symptoms • Leaf spots • Blight • Canker • Dieback • Root rot • Damping-off • Basal stem rot • Soft or dry rot • Anthracnose • Scab • Decline • Excessive growth symptoms • Clubroot • Galls • Warts • Witches’ brooms • Leaf curls • Additional symptoms • Wilt • Rust • Smut • Mildew

19. Fungal Symptoms Anthracnose- Pumpkin Anthracnose- Strawberry Sherrie Smith, University of Arkansas, Cooperative Extension Sherrie Smith, University of Arkansas, Cooperative

20. Symptoms caused by bacteria: • Galls: crown, twig, or cane • Hairy root • Soft rots • Cankers • Wilt • Scab • Blight • Leaf spots • Root nodules of legumes • Fire blight Sherrie Smith, University of Arkansas Cooperative Extension

21. Bacterial Symptoms Cabbage Black Rot • Watermelon Bacterial Fruit Blotch Sherrie Smith, University of Arkansas, Cooperative Extension

22. Symptoms caused by viruses: APLPV - American Plum Line Pattern Virus - Plums • May occur on any part of plant • Stunting • Premature death • Mosaics • Mottling • Streak • Ring or line pattern • Vein clearing • Vein banding • Chlorotic spots • Ring spots Sherrie Smith - University of Arkansas, Cooperative Extension

23. Pictures of Viral Symptoms Bean- Yellow Mosaic Virus • Tomato-Tobacco Mosaic Sherrie Smith, University of Arkansas, Cooperative Extension http://www.avrdc.org/LC/tomato/tomv/html

24. Some Symptoms caused abiotic diseases: • Low temperature • Late frost tip or bloom necrosis • Bark split • Internal branch necrosis • Winter drying of evergreens • Cold water rings • Leaf margin necrosis • Frost injury to fruits • High temperature • Sunscald on fruit • Water core • Blossom end rot (citrus) • Light • Etiolation (low light) • Scald (high light) • Low moisture • Leaf scorch • Wilting • High moisture • Flood damage • Oedema • Rot • Low oxygen • Black heart of tubers

25. Some Symptoms caused abiotic diseases: • Herbicide injury • Leaf or fruit deformities • Chlorosis • Necrosis • Stunting • Death • Air pollution • Chlorosis • Bleached leaves • Stunting • Leaf margin necrosis • Premature defoliation Ozone-damaged plant (left) and normal plant (right) Grazon Damage Sherrie Smith, University of Arkansas, Cooperative Extension Photo courtesy NARA, photographer Gene Daniels/U.S. EPA

26. Managing Plant Diseases • Manage cropping system in a way that prevents disease from occurring • Identify disease • Biotic or abiotic • Fungi, bacteria, virus, or nematode • Foliar or soil-borne • Take disease triangle into consideration: • Improve quality and ability of host to withstand disease • Reduce or eliminate populations of pathogens • Encourage environmental conditions favorable for hosts and unfavorable for pathogens

27. Why is Disease ID Important? • Altering irrigation system to reduce leaf wetness will help against foliar disease, but not soil-borne disease • Crop rotations affect soil-borne disease, but not wind- or insect-dispersed diseases • Fungicides control fungal disease, but not viruses

28. Sanitation: A Key Strategy to Disease Prevention • Plant in sites free of disease • Clean equipment to prevent spread of disease through fields • Clean pruning tools in 10% bleach solution between cuts • Remove crop residue to reduce inoculum buildup • Remove weeds that may serve as pathogen host • Prune diseased portion from plants • Remove severely infected plants from field • Prevent further spread of viruses • Properly dispose of infected debris • Place infected debris in center of hot compost heap • Burn debris • Place in sealed container in trash

29. Cultural Practices to Improve Host Health • Choose resistant cultivars • Avoid excess or deficient crop nutrition • Use transplants rather than seeds to avoid exposure to soil-borne seedling diseases • Plant seeds shallowly to limit pathogen exposure • Correctly prune woody plants to improve air circulation and light infiltration • Scab resistant apple cultivar ‘Liberty’ (left) with susceptible cultivar ‘McIntosh’ (right)

30. Cultural Practices that may reduce pathogen presence • Adjust soil pH • Liming negatively affects some fungal pathogens (e.g. club root ) • Increasing pH inhibits survival of some bacteria (e.g. scab, cotton root rot) • Prune out diseased portion of plants to avoid further spread • Crop rotations break cycle of certain pathogens • Spatially: move location of species within field • Temporally: grow different species from year to year • Keep in mind many pathogens attack numerous species within a plant family

31. Cultural Practices that affect environmental conditions • Use appropriate types of irrigation • Overhead irrigation encourages spread of foliar disease • Avoid overwatering • Improve soil drainage • Improve air circulation through wider row spacing, decreased planting density, and pruning • Time tasks appropriately • Cool soils slow germination of many seeds (e.g. corn, beans), increasing susceptibility to soil-borne disease • Late-season pruning or fertilization discourages hardening-off, increasing occurrence of abiotic disease (e.g frost injury) • Post-harvest cold storage to delay growth of soft rots

32. Physical Control • Soil solarization • Increased temperatures due to solar heat kill many soil-borne pathogens near soil surface • Cover soil with clear plastic • Soil temperatures may reach 52°C

33. Biological Control • Limited options for disease control • Increase diversity of soil microbes through proper soil management and addition of organic matter • Cross-protection • Inoculation of plant with mild strain of disease to provide protection against more virulent strains • Example: Galltrol-A®; nonpathogenic strain of Agrobacterium; protects against crown gall • Coniothyriumminitans • Fungal pathogen of Sclerotiniasclerotiorumand S. minor (cause of white mold on cole crops, carrots, and beans • OMRI-Listed product: Contans® WG • Other control

34. Chemical Control • Potassium-, Sodium-, or Aluminum-Bicarbonates • Formulations differ in efficacy against certain diseases (e.g. Potassium bicarbonate more effective in control of powdery mildew) • Studies have found a variety of concentrations most effective, ranging from 0.5-2% • Some benefit seen from addition of surfactants • Foliar burning resulted when concentration too high • OMRI-Listed products: Kaligreen® and MilStop® broad spectrum foliar fungicide

35. Chemical Control • Sulfur : prevents fungal spores from germinating; phytotoxic • Also has some insecticidal and acaricidal properties • Toxic to beneficial insects, fish, mammals • Should not be used if oil has been sprayed in the previous month

36. Chemical Control • Lime-sulfur: kills recently germinated fungal spores • phytotoxic • Spraying during high temperatures (>85F) increases phytotoxicity • Toxic to mammals • Copper: inhibit growth and germination of spores • phytotoxic • Labeled for use on over 100 crops to control fungal and bacterial diseases • Should be used with care due to toxicity to several non-target species • OMRI-Listed products: Champion WP ®, Crop Clean COCS ®, Britz Copper Sulfur 15-25 Dust ®, Nordox 75WG ®, Concern® Copper soap Fungicide, Cueva Fungicide Concentrate ®, Cueva Fungicide Ready to Use ®, Lilly Miller Ready to Use Cueva Copper Soap Fungicide®

37. Resources http://www.longislandhort.cornell.edu/vegpath/photos/index.htm http://ipmnet.org/plant-disease/glossary.cfm http://plantpathology.uark.edu/2539.htm http://plantclinic.cornell.edu/ http://www.ag.auburn.edu/hort/landscape/exam_pics.html#diseases http://www.nysaes.cornell.edu/pp/resourceguide/

38. Acknowledgements This presentation address general organic production practices. It is to be to use in planning and conducting organic horticulture trainings. The presentation is part of project funded by a Southern SARE PDP titled “Building Organic Agriculture Extension Training Capacity in the Southeast” Project Collaborators • Elena Garcia, University of Arkansas CESHeather Friedrich, University of ArkansasObadiah Njue, University of Arkansas at Pine BluffJeanine Davis, North Carolina State UniversityGeoff Zehnder, Clemson UniversityCharles Mitchell, Auburn UniversityRufina Ward, Alabama A&M UniversityKen Ward, Alabama A&M UniversityKaren Wynne, Alabama Sustainable Agriculture Network