Diagnosing Plant Problems

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Diagnosing Plant Problems

The Art and Science of Diagnosing

Plant Problems



• Adapted from “Plant Disease Diagnosis” by M. B.

Riley, M. R. Williamson and O. Maloy. In: The Plant Health

Instructor . DOI:10.1094/PHI-I-2002-1021-01

• Used by permission of the American

Phytopathological Society



• http://coloradoipmcenter.agsci.colostate.

edu



Plant Problem Diagnosis

Diagnosis –process used for the

identification of problems; consider it

‘CSI’ for plantsTools:

– Plant sciences, especially plant pathology

and entomology – Arts of investigation and detective work



Field Sample Collection for Diagnosis

• Items that are handyin your toolbox:

– Hand lens/ magnifyingglass;

–

Pocket knife; – Soil probe;

– Shovel;

– Small notebook

w/pencil; – Plastic baggies;

– Small saw/handpruners



Plant Problem Diagnosis:

Preliminary Considerations

Know Normal Appearance

of Plant

–

Plant identification.• Scientific vs. common

names

• Variety or cultivar

– Recognize healthy plant

appearance.

• What’s normal?



Plant Problem Diagnosis Steps

Consider the Possible Agents:

– Abiotic – non-living agent

• Damage from chemicals,

weather, mechanical• Nutritional problems

– Biotic – living agent

• Pathogens - parasitic

microorganisms that cause

diseases• Pests – insects or mammals

feeding on or damaging plants



Plant Problem Diagnostic Steps

Review cultural

practices:•

Proper plantingtechnique

• Fertilizer and pesticide

application

• Irrigation frequency




Review environmental

conditions:•

Temperature extremes• Drought or excess rain




Ask questions (for example):

• When was the problem noticed?

• Was the damage sudden or gradual?

• How old are affected plants?

• Percentage of plants affected?

• What is the degree of injury?






Observe patterns:

– Determine prevalence

of problem

Large area/All plants

– generally abiotic

– Scattered, localized –

generally biotic – Check for distribution of

symptoms



Observation of Patterns

Hot spots or pockets

biotic or abiotic



Observation of Patterns

Symptoms distributed in a

large area.Damage pattern is

uniform.

Winged Euonymus damaged

by excessive soil moisture





What part of the plant is damaged?

• Leaves, stems, roots,

fruit etc.



Check for Symptoms and Signs

Symptoms

• Plant reactions or alterations of a plant’s

appearance due to a disease or disorder

Signs

• actual pathogen, parts or by-products seen on

a diseased host plant



Symptoms

Identify and classify symptoms:

• Underdevelopment

• Overdevelopment

•Necrosis or death

• Alteration of normal appearance

• Wilting



Symptoms

Underdevelopment

• Stunting of plants,

leaves• Shortened internodes

• Inadequate

chlorophyll production• Caused by many types

of pathogens

Root knot nematodes cause

stunting of tomato plants



Symptoms

Overdevelopment

• Overgrowth of leaf

tissue causesthickening and

distortion

– Example: Leaf curls

caused by the fungusTaphrina

Peach leaf curl

Chokecherry leaf curl



Symptoms

Overdevelopment• Galls form on all plant

parts, caused by manypathogens.

• Swelling

Crown gall

Root knot nematode



Symptoms

Overdevelopment

• Witches broom

• Fasciation

Juniper broom rust

Bacterial fasciation of

geranium



Symptoms

Overdevelopment

• Blisters

– Oedema or edema is

caused by water

accumulation in tissue

resulting from high

relative humidity andhigh soil moisture

Oedema of camellia, a

physiological disorder

Used by permission of M. Willliamson



Symptoms and Signs

Tissue Necrosis

• Fungal leaf spots

• Usually round, notvein-limited

• Sporulation or

mycelium may beevident

Anthracnose diseases of cucurbits



Symptoms and Signs

Tissue Necrosis

• Bacterial leaf spots

– Often water-soaked or

transluscent

– Often vein-limited,

giving angular shape

– Bacterial “flow”

observed under

microscopeBacterial leaf spot of Pumpkin and

squash



Symptoms and Signs

Tissue Necrosis

• Fruit rots

–Firm or soft andwatery

– Colors vary

– Fungal spores may be

present – Fungal and bacterial

causes Brown rot of peach, caused by

Monilinia fruticolaPhoto: Clemson University - USDA Cooperative Extension

Slide Series, , www.ipmimages.org



Symptoms

Tissue Necrosis

• Cankers = localized

necrotic lesions – Sunken or swollen or

both

– Mainly caused by fungi

and bacteria



Symptoms

Tissue Necrosis

• Blight = rapid death or

dieback.

Photo: Robert L. Anderson, USDA Forest Service, www.ipmimages.org

Fire blight caused by Erwinia amylovora



Symptoms

Tissue Necrosis

• Dieback - many causes

– Girdling cankers. Follow

dieback to detect

– Dieback pathogens w/out

cankers

– Root problems

–

Mechanical, chemical orcold damage

Pitch canker of Virginia pine, caused by

Fusarium subglutinansPhoto: Edward L. Barnard, Florida Department of Agriculture and

Consumer Services, www.ipmimages.org



Symptoms

Tissue Necrosis

• Root Rots

– Root lesions

– Darkening and softening of

roots

– Sloughing off of outer root

tissue

–

Yellowing of foliage andstunting of plants



Symptoms

Tissue Necrosis

• Damping off

–Rapid death ofseedlings and cuttings

– Stem infected at soil

line, seedling topples

–Spreads rapidly undercrowded conditions

– Mainly fungal agentsDamping off of tobacco, caused by

Rhizoctonia spp. and Pythium spp.

Photo: Clemson University - USDA Cooperative Extension SlideSeries, www.ipmimages.org



Symptoms

Wilting

• Biotic Factors –

Root, crown, stem rots• Mainly fungal and bacterial

causes

– Vascular wilt pathogens

• Mainly fungal and bacterial

causes

– Root, crown, or stem

damage from insects or

animals



Symptoms

Abnormal Color or

Appearance

–

Mottling – Mosaic

– Crinkling

– Stunting

– Vein clearing – Flower break

– Ringspots

T. Lundsgaard, Dept Biology,

KVL, Denmark



Symptoms

Alteration of normal

appearance distortion

• Abiotic causes• Chemical damage

• Nutritional deficiencies

Used by permission of M. Williamson

Cotton damage by the herbicide 2,4-D



Changes in ColorYellowing (Chlorosis)

• Generalized degeneration

or disorganization of

chloroplasts• Multiple causes (abiotic,

infectious agents)

• Yellowing symptoms are

often not diagnostic butcan be used in

conjunction with other

symptoms

Symptoms



Reddening

• Phosphorus deficiency

• Cold temperatures

• Viruses andPhytoplasmas



Symptoms

– Be aware of symptom variability.

– May have more than one problem.

– More than one pathogen may be involved.

– Environmental conditions can affect symptom

expression.

– Host genetics and physiology can effect symptom

expression. – Primary vs. secondary symptoms



SignsFungal signs

– Evidence of pathogen

on tissue.

– Spores, mycelium or

fruiting bodies

White mycelium of Armillaria sp. on

tree trunk affected by Armillaria root

and stem rot.Photo: USDA Forest Service Archives, USDA Forest Service,

www.ipmimages.org



Signs

Fungal signs

– Powdery mildew fungiform mycelia and

spores on tissuesurface.

– Powdery material rubsoff.

–

Leaves often distorted,discolored

Dark, round fruitingbodies form in fall

Oidium sp. causing powdery

mildew on Viburnum suspensum.Used by permission of M. Williamson



Signs

Bacterial signs

– “Streaming” from freshly

cut stem in water.

– “Stringing” from cut stemspushed together, then

pulled apart.

– Bacteria “flow” observed

from tissue mount on

compound microscope. – Bacterial ooze can be

observed on-site with some

diseases

Bacterial streaming from tomatoinfected by Ralstonia solanacearum.Used by permission of M. Williamson




• Consult literature resources for

possible diseases and disorders:

– Host and pathogen indexes

–Websites providing information (be careful withyour sources)

– Books with background info and host/pathogen

lists

–Compendia for information on specific crops

– CSU fact sheets

– Other Land Grant University publications



Final Diagnosis

• Indicate confidence of diagnosis

– Certain, probable, etc.

• Provide a management strategy (This is what your

client really wants!)• Provide options – let the client make the final

decision

– Can the problem be managed by cultural practices alone?

– Are chemicals necessary?

• Organic vs Synthetic?

Diagnosing Plant Problems

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