Plant disease. Plant Diseases: Learning objectives: Plant Disease: Any physiological or structural abnormality that is harmful to the plant

Transcription

1 Plant disease Plant Diseases: Identification and Control Melodie Putnam Extension Plant Pathologist Learning objectives: Difference between biotic and abiotic diseases and their manifestation Difference between fungi, bacteria, nematodes, and viruses Concepts embodied by the disease triangle Principles of disease control Plant Disease: Any physiological or structural abnormality that is harmful to the plant s biotic (infectious) s abiotic (non-infectious) 1

2 The expression of disease on a plant Symptoms are related to plant function Signs are visual manifestations of a disease (fungus, virus, bacteria, etc.) 2

3 Signs: The physical evidence of a pathogen Abiotic factors are noninfectious Examples. Characteristics of an abiotic disease Regular or uniform manifestation Sunburn on blueberries 3

4 Uniform pattern except some flats had symptoms and other flats did not possibly P disorder. 4

5 Nectria canker Silk Tree (sin) Winter damage Nutrient disorders: calcium N deficiency Youngest Oldest Apple: Bitter pit Tomato: Blossom End Rot 5

6 Scaveola Dracena Petunia What is this? Symptom not always diagnostic. 6

7 Injury does not progress over time Will not move from plant to plant Weather related: Sunscald on tree and scorch on dogwood leaves 7

8 May affect many different species of plants Abiotic injury Pattern of problem? Possible causes? Pattern of problem? Abiotic injury Tends to uniform expression on plants Can affect a variety of different plants in an area Not caused by a living pathogen Possible causes? Mechanical injury Nutrient disorder Temperature or other weather phenomena like hail Herbicide injury Others Biotic agents of disease Fungi Bacteria Viruses Nematodes 8

9 10% of fungi are pathogens Most reproduce via spores. Fungi 9

10 Siricoccus fruiting body A needle fungus of spruce and hemlock Fungi are spread by: Infected plants, plant debris, & soil Wind Equipment Water splash Seed Insects Bacteria Require natural openings to infect Do not produce spores; reproduce by division Do not move on their own 10

11 Bacteria are spread by: Nematodes Infected plant material & soil Water splash Pruning tools Insects Seed 11

12 Nematodes Are microscopic unsegmented roundworms. Reproduce via eggs. Nematodes Infected plants, plant debris, and soil Anything that moves soil Control Fungi, Bacteria, Nematodes v Clean planting material v Removal of affected tissue v Crop rotation (soil-borne) v Seed treatment (seed-borne) v Plant resistance v Biological control v Chemical control 12

13 Viruses t t t Viruses Are submicroscopic Are obligate parasites Can t reproduce on their own Viruses Are spread by: Infected plants and plant debris Grafting Insects Nematodes Humans Control v v Viruses Clean planting material Removal of affected plants Viral diseases are systemic: Once infected there is no cure 13

14 Parasitic plants t Reproduce via seeds. t Are spread by: Exploding fruit Birds Infested crop seed lots Lichens are NOT parasitic Irregular or nonuniform manifestation = biotic infection, usually. But it can spread to cover the whole area as it progresses. 14

15 Affects few species of plants Principles of disease control Host Host Disease Environment Pathogen Environment Pathogen 15

16 Exclusion v Pathogen-free planting material Very important with perennial plants Exclusion v Quarantines, e.g. Sudden Oak Death Environment Host Pathogen Avoidance Resistance v Plant material adapted to the area (oranges are out) - right plant, right place Susceptible Tolerance Host Healthy v Plant properly v Twisted roots Environment Pathogen 16

17 Diseases Red thread resistance Apple scab fungus. Resistant varieties available Red Fescue Ensylva Hard Fescue Eradication (Sanitation) Goal: Reduction of the inoculum load P. Mildew on zinnia and SEM photo of conidia from lesions Protection v Is a tool used in conjunction with other methods. Examples: s Chemicals s Biocontrol agents s Seed treatments 17

18 Biological Control NoGall (bac.) PlantShield (fungi) Contans (bac.) Messenger (bio) Principles: Competitive exclusion Predation Antibiosis Plant growth promotion Biological Control Limitations: - Must be in place prior to planting - Do not act the same as chemicals - Not universally effective Advantages Less toxic May be only option 1. Protectant/contact no systemic activity v v Fungicides are of two types: Coats leaves to prevent infection captan chlorothalonil (Daconil 2787) copper compounds Kills pathogen on contact horticultural oils, soaps sulfur compounds, salts 2. Curative/systemic v Must be applied before or soon after infection occurs v Kills the pathogen once infection has occurred Ex: Immunox 18

19 Understanding the pathogen and how it survives on its host: Key to control Aerial fungal diseases - Fungi that overwinter on leaves, branches, twigs or buds Scab 19

20 Incense-cedar rust Brown Rot 20

21 Black spot Powdery mildew on grapes 21

22 Powdery mildew on grapes cont. Powdery mildew on squash Powdery mildew Not a disease: Mites Bladder gall mite on maples Erineum mite on grapes 22

23 Cankers Management of aerial fungal pathogens? Apple : Anthracnose Fungal problems Damping-off - Soil-borne fungi 23

24 Sclerotinia 24

25 Phytophthora root rot: raspberries Verticillium Verticillium wilt 25

26 Management of soil-borne fungal pathogens? Resistant varieties and good cultural techniques Bacterial blight of lilac Bacterial Diseases 26

27 Bacterial canker of stone fruits Crown gall Crown gall biology 27

28 Crown gall biology cont. Insect galls Viral diseases 28

29 Nematodes Plant Disease Handbook 29