Module 3: Diagnosis

Requirements to do diagnostics

• Organized, logical approach• Able to ask the “right” questions• Access to reference materials• Knowledge of local soil and weather

characteristics• Common sense and a “detective” enthusiasm

Steps in diagnosing plant diseases

1. Identify the plant2. Define the problem3. Develop list of potential disease candidates4. Refine diagnosis5. Confirm the Diagnosis: Get additional help

Step 1: Identifying the plant

• ALWAYS identify the plant to most appropriate level possible (Species, Variety, etc.)

• KNOW what it is suppose to look like at the current time of year.

• Learn about difference characteristics among cultivars.

Normal plant development is NOT a disease problem

Is there a problem?• Normal development or plant problem?

Step 2: Define the problem

• Tissue affected: Leaves, Stems, Roots, etc.• Symptom Description: Leaf Spots, Canker, Blight, etc.• Part of the Plant affected: Top, Bottom, New Growth, Old

Growth, etc.• Timing and duration of problem: Spring, Summer, 3 wks ago, etc.• Site of problem: Front or back yard, shade or sun, low or high

ground, etc.• Stressful Conditions: Excessive water, etc.

• Collect as much information as possible during the initial contact, follow up with more questions as necessary

• Ask questions that are applicable to the situation

Step 2: Define the problem

Step 3: List of suspects

• BIOTIC– Symptoms is usually

scattered– Symptoms develops

gradually over time (on individual and whole plantings)

– Sign of pathogen is observable

• ABIOTIC– Symptoms are uniformed– Generally appear all at one

time– Does not appear to spread– Affects more than 1 type

of plant in immediate area

List of Suspects

• Biotic– Bacterial– Fungal– Nematode– Virus– Arthropod (Insect,

Mites, etc.)

• Abiotic• Cultural:

– Improper management– Chemical Toxicity

• Environmental / Physiological– Soil, Water, Light,

Temperature– Nutrient Imbalances

Gathering information and use keys to find potential suspects

• Review:– Master Gardener Handbook– Extension Publications– Extension, University, or Government Websites– Text books– Plant Disease Compendium (available from apsnet.org)

• Use a key or diagnostic tool – Plant Problem Diagnostic Key (J. Johnk – see handout)– Tomato or Cucurbit Problem Solver (aggie-horticulture.tamu.edu)

– Web search: ‘name of the plant’ diseases extension

Step 4: Refining diagnosis

• Gather known information and Compare with gathered information

– Did what I see and find out about the problem MATCH what I read about this suspect?

Step 5: Confirm Diagnosis:Get additional help

– Other Master Gardener– County Agent– Plant Pathologist– The Texas Plant Disease Diagnostic Lab– Use Additional literature (books/reliable websites)

The Diagnosis

• Did you find a perfect match?• Many times we have to use the available information to

select the most likely causal agent• Diagnosis are not always definitive • Take the opportunity to educate the client about proper

plant care and horticultural practices • Teach them ways to avoid disease• Promote the Earth Kind Environmental Stewardship

Program to avoid future problems

Scenario

Time: Late May, 2002

My oak tree is dying. It is covered in yellow brown spots and the leaves are somewhat curled.

OAK LEAF BLISTER

Scenario

Time: Early SeptemberConditions: Wet spring, hot

summer. Soil are alkaline and heavy.

My pittosporum just turn brown and died within 1 week. What happened? Are my other plants going to die?

Cotton Root Rot

Scenario

Time: SpringI just notice that the rose I planted

last year had some funny stuff growing at the soil line. It feels hard and stony. What is it? It is going to kill my plant?

Crown Gall

ScenarioTime: AugustThe leaves of my cucumber vine looks spotty. Soon

after they have reddish-brown (dead) spots on them. On the back is fuzzy.

Downy Mildew

Scenario

Time: Late October

I was clearing out my garden when I pulled out my tomato plants and notice that their roots were galled. I also remember that my tomatoes did not do too well this year.

Root Knot Nematode

Scenario

Time: Late August

My maple tree is showing scorching symptoms at the margin of the leaf. It is all over the tree especially at the tips. I read on the internet that it may be a bacterial disease.

Physiological/Environmental

ScenarioTime: Mid September

I had a pretty nice stand of tomatoes. It was ripening just nicely, but then it started to have big white blotches then it just rotted. It occurs on many of the fruits but not all of them. My eggplant also started to look bad about the same time. What is going on?

Sun Scald

Scenario

• Time: Summer My Zinnias are having

this spots that begins at the lower leaves and seems to be traveling upwards. Is it a bacteria?

Xanthomonas campestris pv. zinniae

Define the problem (Information gathering)

1. When did the symptoms first appear?2. Have the same or similar symptoms occurred before?3. Is there any pattern to symptom occurrence: in the landscape

(perhaps in low areas only), or on the plant (both old and new foliage affected equally)?

4. Is more than one kind of plant (species or cultivar ) affected?5. What is the appearance of the roots?...6. Are cankers, holes, or wounds evident on the stems?

- Do the holes or wounds follow a pattern or are they random?

Define the problem (Information gathering)

7. What percentage of leaves are affected on the plant?8. Where are the leaves affected? Top, Bottom, Inner, Outer9. What is the appearance of the leaves? Color?10. Are the flowers or fruit normal in appearance? Are any spots or

deformed areas apparent?11. Where is the plant located?12. How many hours of sun does the plant receive?13. Has there been any significant disturbance or compaction that

has occurred recently?

Define the problem (Information gathering)

14. Has the soil or plant been exposed to:pool water, soil sterilant, fence stain, heat from appliances, etc.

15. What is the condition of the soil?dry (how long), wet (how long), compacted, etc.

16. What is the soil texture: sand, silt or clay?17. What is the soil pH? Organic Matter content? Mulch?18. Is the soil well drained?19. How often and how much fertilizer do you use?20. Was there any application of pesticides in the vicinity: herbicides,

insecticides, fungicides, etc.21. Did you follow the labeled instructions?

Define the problem (Information gathering)

22. How many inches of rainfall did you receive during the past ________?

23. Have you provide supplemental irrigation? How much and how often?

24. Do you have a sprinkler system? Do you know what it is programmed for?

25. Do you have overhead sprinklers watering you landscape plants? Or just the turf grass?

26. Do you have city water or well water? What is the quality of the water? Is there high levels of total soluble salts?

What is wrong here?

Module 4: Solutions to disease problems

Disease Control Principles

• Resistance • Exclusion• Protection • Eradication• Avoidance• Therapy

ResistanceUsing inherent traits of the

plants against diseases– Resistant traits– Adapted traits

• Fast growing

– Quality traits• High yields

ExclusionKeeping the pathogen out– Using only healthy plants– Buying certified plant material– Aware of what materials are brought into

your garden– Filtered greenhouse– Maintaining clean equipment– Quarantine & Inspection

Protection

Using a barrier to protect plants from diseases– Chemical barrier– Biological barrier– Physical barrier–Modified environments

EradicationKilling or getting rid of the pathogen– Removing and/or destroying diseased plant

debris (Sanitation or roguing)– Fumigating area of planting– Do not plant a host for some time (rotation)– Solarization

Avoidance

Avoiding the pathogen or situation that cause disease– Different planting sites– Different planting times– Using adapted varieties– Carefully watering

Therapy

Helping the plant to heal– Pruning out diseased

material– Systemic chemicals

Cultural controls– Proper Horticulture Practices !!!!– Improve soil quality

• “Healthy Soil, Healthy Plants”• Cover crops, compost, mulch• Ensure proper drainage• Fertilization• Reduces splashing of soil borne diseases• Helps regulate soil moisture• Helps encourage beneficial microbes

– Irrigation• Proper watering methods to minimize plant stress• Reduce leaf wetness

Cultural controls

• Sanitation– Removing disease plant material from growing area. • Pruning out disease branches• Raking and destroying leaves with fungal spots• Weed control

• Crop Rotation

What is Landscape IPM?

• Integrated Pest Management is a strategy of managing pests that is designed to meet individual goals in the most economically and environmentally sound manner possible using a combination of control tactics.

http://txipmnet.tamu.edu/

http://earthkind.tamu.edu/

IPM Tactics

• Cultural control • Biological control • Mechanical control • Chemical control

IPM Decision-Making6 step process:1. Identify the problem or pest2. Determine the severity of the problem and determine if the action

threshold has been reached.3. Assess the management options (do nothing, cultural, biological,

chemical control)4. Select and apply one or more options5. Measure the success of options employed6. Record the results

Pesticides TerminologyProtectant:

to be applied and is most effective prior to infectionCurative:

can be applied post infection and is capable to curing plantBroad spectrum:

affects many different pathogensNarrow spectrum:

affects only one or few specific pathogensContact fungicide:

is only effective when in contact with fungiSystemic fungicide:

is able to be taken up and moved through out a plant

When prescribing chemical treatments

• Maximize pesticide performance– Use the least amount in the most efficient way

“More is NOT always better!”– Consider environmental condition when spraying– Use proper spraying techniques– Follow the label, It’s the Law!

Extension publication of interest

• E-159 Chemical for Plant Disease Control at Home.

• L-2016 Non-Chemical Control of Plant Diseases in the Home Garden

• Additional Extension Publications can be found at:

Agrilifebookstore.org Click Advanced Search

Internet Resources

• Plantclinic.tamu.edu• Plantpathology.tamu.edu• Aggiehorticulture.tamu.edu• Apsnet.org• Web Search: Plant Disease Extension• Web Search: “Plant Name” Disease Extension

Plant Pathology Images

Anemone sp. Little Princess

Myrothecium leaf spot (Myrothecium

roridum)

Cold Injury from drops of cold dew

Happy Master Gardening!