Objectives

• To identify plant diseases common to horticulture and agronomic crops.

• To reveal the impact plant diseases can have on fruits, plants and agricultural crops.

• To analyze methods of plant disease control.

Table of Contents• Introduction to Diseases• Bacterial Diseases

o A-Bo C-Z

Main Menu

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Disease• Is any condition interfering with normal

growth and development• Is caused by living or non-living agents• Can affect any area on a plant

Disease: Living Agents• Are referred to as plant pathogens

o anything causing harm to plants• Include microorganisms, such as:

o fungio bacteria

Fun Fact : Another term for living agent is biotic agent.

Fungal Diseases• Spread from plant-to-plant via

wind, insects, rain, soil and machinery

• Can be transmitted by seeds• Can be waterborne• Are most common and easiest to

treat• Treatment can include:

o sanitationo reduce wateringo increase air flow

Fungal Diseases• Usually start with spotted or discolored

leaves and stems o dry, brown margins and dead tissue

or necrotic lesions• Are controlled with dusts or sprays• Are nearly impossible to eliminate if not

treated immediately, especially soil-borne disease

Mildews• Are a form of mold• Are commonly found in damp, moist,

shaded places• Affect leaves, stems, buds, flowers and

fruitso leaves will turn pink, blue or purple

and drop prematurely• Are usually white, gray, green or black

Life Cycle of Fungi• Includes four stages:

o spore productiono sporeo spore germinationo hyphal growth

Life Cycle of Fungi

Bacterial Diseases• Are easier to prevent rather than cure• Enter plants through wounds or natural

openings, such as the stomata• Easily occur under the following

conditions:o high humidity o poor air circulationo irregular wateringo poor soil drainageo fluctuating temperatures

Bacterial Diseases• Spread by:

o infected seedso animals and birdso irrigation water and raino machinery

• Have symptoms such as:o leaf spotso blightso wilting

Life Cycle of Bacteria

Disease: Non-Living Agents• Include:

o environmental stress on plants, such as:

• air pollution• drought• hail• wind

o cultural careo toxic chemicalso viruses

Fun Fact : Non-living agents are also referred to as abiotic agents.

Viruses• Are microscopic, infectious agents

consisting of a protein coat surrounding nucleic acid

• Multiply in cells of living hosts• Are recognized by the following

symptoms:o leaf curlingo leaf discolorationo ring spots on leaveso stunted growth

Viruses• Can be prevented by:

o planting disease-resistant varieties

o controlling pests carrying viruses

o removing and destroying infected plants

o controlling weedso handling foliage when dry

• Can be spread by:o infected insects, plants and

microorganisms

Fungicides• Are specific pesticides for fungal diseases

in plants• Are used to:

o control fungi in crop standso increase productivity of cropso increase storage life of plants and

produce

Fungicides• Should be applied as soon as symptoms

occur or with coated seeds• Can be applied in the following forms:

o dusto gaso granuleo liquid

Fungicides• Are applied on:

o bulbso foliageo harvested produce o rootso seedso soil

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Assessment1. Which area of a plant can be affected by disease?

A. All areasB. Only the stemC. Only rootsD. Only leaves

2. What is another term used when referring to a living agent?

A. Living specimenB. Bacterial agentC. Fungal agentD. Biotic agent

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Assessment3. All but which of the following are treatment methods for fungal diseases?

A. Increasing air flowB. Increasing waterC. Reducing waterD. Sanitation

4. Which of the following can NOT spread bacterial diseases?

A. WindB. Infected seedsC. BirdsD. Machinery

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Assessment 5. What type of disease is the easiest to treat?

A. BacterialB. FungalC. VirusesD. All are equally treatable

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Angular Leaf Spot • Scientific Name: Pseudomonas

lachrymans• Characteristics:

o infects cucumbers, melons and squash

o usually appears on fruit in middle stage of development

Angular Leaf Spot o causes small, saturated areas to

develop on stems and fruit• areas appear tan, but turn

gray and white as disease progresses

o forms holes in leaf as dead tissue falls off

o causes lesions between water-saturated veins

Angular Leaf Spot • Environmental conditions:

o humidityo strong windo splashing watero infected irrigation water

Angular Leaf Spot

• Prevention methods:o choose plant varieties suitable for

climateo practice crop rotationo destroy infected plants o avoid overhead watering systemso provide proper amounts of fertilizer

Angular Leaf Spot • Treatment methods:

o fungicides which contain:• copper hydroxide-based, such

as Champion®, Kocide® 101 and Bordeaux® mixture

Bacterial Blight

• Scientific Name: Xanthomonas campestris

• Characteristics:o affects a variety of crops, such as:

• lima beans• soybeans• snap beans

o forms saturated spots on leaves• spots turn pale-green or yellow

then dark-brown

Bacterial Blight o causes leaves to die and fallo causes stems to wilt as disease

progresses• Environmental conditions:

o high humidityo wet weather

Bacterial Blight • Prevention methods:

o use crop rotationo provide space for air circulationo use seeds from non-infected plantso avoid handling plants when wet

Bacterial Blight • Treatment methods:

o fungicides which contain:• copper hydroxide, as found in

Champ® or Kocide® 200

Bacterial Leaf Scorch • Scientific Name: Xylella fastidiosa• Characteristics:

o commonly affects trees, such as:o elmo mapleo walnut

o dries leaves outo turns margins browno affects outer leaves severely

Bacterial Leaf Scorch • Prevention methods:

o deep root systemso prune regularlyo water regularly

• soil should be deeply watered

• fertilize trees of low vigor

Bacterial Leaf Scorch

• Treatment methods:o no available treatment

• follow prevention methods

Bacterial Soft Rot

• Scientific Name: Erwinia carotovora• Characteristics:

o affects many vegetable plants, such as:

• carrots• corn• onions• potatoes

Bacterial Soft Rot

o affects potatoes in the following ways:

• tissue becomes saturated and wet

• rotten tubers acquire odor in later stages of disease

Bacterial Soft Rot

o affects onions in the following ways:• symptoms occur inside onion

during storage• infected bulbs are soft and

pale-brown• contaminated onions produce

a foul odor• infected onions have a soft

neck o causes taproots of carrots to decay

and become soft

Bacterial Soft Rot

o affects corn in the following ways:• uppermost leaf tips dry out • decay starts at top of plant and

moves down• stalks turn brown, become

water-soaked and eventually fall over

• produces an odor

Bacterial Soft Rot • Environmental conditions:

o warm weathero humidityo high level of soil moistureo insect wounds

Bacterial Soft Rot • Prevention methods:

o use crop rotationo handle gentlyo mix compost with soil to increase

beneficial bacteria populations• Treatment methods:

o seed treatments which contain:• thiophanate-methyl or

thiophanate-methyl, with the addition of mancozeb, such as Tops® MZ®

Bacterial Spot • Scientific Name: Xanthomonas

campestris pv. vesicatoria• Characteristics:

o irregular spots on tomato plants and pepper leaves

o younger leaves more susceptibleo weakens plantso causes decayo common in midwestern and eastern

United States

Bacterial Spot • Environmental conditions:

o very warm, wet conditions

Bacterial Spot • Prevention methods:

o use disease-free seedso remove weedso fertilize o use crop rotationo provide space for air circulationo use drip irrigation and soaker hoses

to maintain dry foliageo cover soil with mulcho remove infected plants

Bacterial Spot • Treatment methods:

o fungicides which contain:• mancozeb and copper, such as

Yates™

Bacterial Wilt

• Scientific Name: Ralstonia solanacearum• Characteristics:

o leaves turn brown as disease spreads

o streaking in vascular tissueo causes cucumber and squash leaves

to droopo effects young plants firsto results in plant deatho bacteria clogs vascular system

Bacterial Wilt • Environmental conditions:

o infected insects feed on leaves• Prevention methods:

o plant wilt-resistant varietieso sustain proper plant healtho remove infected plants

Bacterial Wilt • Treatment methods:

o no available treatment• follow prevention methods

Blackleg • Scientific Name: Pectobacterium

carotovorum var. atrosepticum• Characteristics:

o forms dark spots on base of stems and roots in cabbage plants

o plants turn yellow, wilt and dieo spread by rain, wind and human

activity

Blackleg

• Environmental conditions:o cool, moist weather

Blackleg • Prevention methods:

o provide space for air circulationo remove weeds o remove infected plantso use crop rotationo prevent injury to cropo choose resistant cultivars

Blackleg

• Treatment methods:o fungicides which contain:

• iprodione, such as Rovral®

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Crown Gall • Scientific Name: Agrobacterium

tumefaciens• Characteristics:

o occurs on roots and stems of many plants

• most destructive in fruit trees and shrubs

• commonly seen in roses

o forms galls at crown and lateral roots

• galls are one-quarter inches to one foot in diameter

• young are tan and have a soft surface

• mature are black and have a very hard surface

o stunts plant growtho turns leaves yellow or brown

Crown Gall

Crown Gall

• Environmental conditions:o cool, humid weather

Crown Gall • Prevention methods:

o avoid plant injuryo avoid contaminated toolso inspect plants carefully and

regularlyo destroy infected plantso plant gall-resistant varieties

Crown Gall • Treatment methods:

o products which contain:• meta-cresol, such as Gallex®

Fireblight

• Scientific Name: Erwinia amylovora• Characteristics:

o destroys trees and shrubso common among fruit treeso identified by tan liquid seeping out

of branches and twigs• liquid darkens with air

exposure, called “bacterial ooze”

Fireblight o causes infected flowers to wilt and

turn black or brown • dead, blackened leaves will

cling to branches during springo forms orange-red streaks on barko dries out and kills wood

Fireblight

• Environmental conditions:o wet, humid weather

Fireblight • Prevention methods:

o avoid heavy pruningo monitor trees regularlyo remove infected plants o plant resistant varietieso provide adequate fertilization

Fireblight • Treatment methods:

o fungicides which contain:• copper products, such as

Bordeaux®

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Galls• Characteristics:

o known as cecidiao abnormal tissue growthso formed by microorganisms and

insects• insects cause galls when laying

eggs or feedingo form on buds, leaves, flowers, twigs,

bark and rootso unattractive, but causes no harm

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Gallso appear in two forms: open or closed

• open are formed by insects with piercing mouthparts

• closed are formed by insects with mandibles

• Environmental conditions:o cool, humid weather

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Galls

• Prevention methods:o use insecticides to control

insect populations

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Galls

• Treatment methods:o no available treatment

• follow prevention methods

Potato Scab • Scientific Name: Streptomyces scabies• Characteristics:

o appears on skin of potato tubers• turns dark brown or black

o forms large circular scabs on potatoes, called “scab lesions”

o usually noticed after harvest or late in growing season

o reduces marketability of potatoes o transmitted by wind and water

Potato Scab

• Environmental conditions:o soil with high organic mattero coarse, textured soilso warm, dry weathero wounded plants

Potato Scab • Prevention methods:

o use crop rotationo do not use compost mixeso keep soil cool and moisto plant disease-resistant varieties

• Treatment methods:o before planting, treat seed tubers

with a seed fungicide which contain:• captan or mancozeb

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Assessment1. On which plant does angular leaf spot NOT occur?

A. CucumbersB. SquashC. MelonsD. Corn

 2. Under which environmental conditions does bacterial blight spread?

A. High humidityB. Low humidityC. High temperaturesD. High winds

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Assessment3. Which prevention method is NOT used to prevent bacterial blight?

A. Crop rotationB. Proper irrigationC. Use non-infected seedsD. Provide space for air circulation

 4. Which of the following can be used to treat bacterial spot?

A. CopperB. SulfurC. ZincD. Lime

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Assessment5. Which region of the country is bacterial spot most prevalent in?

A. NorthwestB. MidwestC. SouthwestC. South

6. Which environmental conditions are best for blackleg to occur?A. Cool, moist weatherB. Warm, wet weatherC. Cool, dry weatherD. Warm, dry weather

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Assessment7. Which part of the plant is affected by crown gall?

A. LeavesB. ThornsC. RootsD. Fruit

 8. Which plant is crown gall commonly seen in?

A. RosesB. Bermuda grassC. Oak treesD. Pine trees

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Assessment9. How does gall harm the plant?

A. Wilts leavesB. Destroys fruitC. Removes fluidsD. Causes no harm

 10. Potato scab is usually noticed when?

A. Before plantingB. During plantingC. During growthD. After harvest

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Final Assessment1. Which type of diseases can be waterborne?

A. FungalB. BacterialC. ViralD. Non-living

 2. Environmental stress on a plant is what type of pest?

A. Non-livingB. ViralC. FungalD. Bacterial

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Final Assessment3. Which type of disease is commonly found in damp, moist and shaded areas?

A. BacterialB. FungalC. VirusesD. Mildews

 4. Which symptom is NOT caused by bacterial diseases?

A. BlightsB. Leaf spotsC. MildewsD. Wilting

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Final Assessment5. Under which environmental condition does angular leaf spot occur?

A. Dry climatesB. Strong windC. Cold weatherD. Standing water

6. Which tree is NOT commonly affected by bacterial leaf scorch?A. ElmB. PecanC. MapleD. Walnut

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Final Assessment7. Which of the following is NOT a characteristic of bacterial soft rot?

A. Foul odorB. Tissues become saturatedC. Leaf tips dry outD. Bacteria clogs vascular system

 8. How can bacterial wilt be treated?

A. FungicidesB. Proper irrigationC. Crop rotationD. No treatment available

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Final Assessment9. On which part of the plant does fireblight cause orange-red streaks?

A. LeavesB. FruitC. BarkD. Roots

 10. How can galls be treated?

A. Remove by handB. Herbicides C. FungicidesD. No treatment available

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ResourcesBiggs, A. R. & Hickey, K. D. (1997). Apple Scab. Retrieved from http://www.caf.wvu.edu/kearneysville/disease_descriptions/omapscab.html

North Dakota State University. McMullen, M. & Stoltenow, C. (May 2002). Ergot. Retrieved from http://www.ag.ndsu.edu/pubs/plantsci/crops/pp551w.htm

Cranshaw, W.S. (August 29 2011). Insect and Mite Galls. Retrieved from http://www.ext.colostate.edu/pubs/insect/05557.html

National Arborists. (2011). Apple Scab. Retrieved from https://natlarb.com/html/apple_scab.html

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ResourcesVann, S. Ph.D.(2006) Plant Diseases. Retrieved from http://www.aragriculture.org/diseases/image_library/default.htm

United States Department of Agriculture. Retrieved from http://www.ars.usda.gov/is/graphics/photos/

Kansas Department of Agriculture. Retrieved from http://www.ksda.gov/plant_protection/

Broome, J. C. & Ingels, C. A. Produced by UC Statewide IPM Program, University of California. (January 2011). Peach Leaf Curl. Retrieved fromhttp://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7426.html

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ResourcesGrove, Gary, Ph.D., Washington State University Extension. Apple Scab. Retrieved from http://gardening.wsu.edu/library/tree005/tree005.htm

Rosenthal, S., Grau, C. & Hudelson, B. (December 28, 2005). Ergot. Retrieved from http://pddc.wisc.edu/factsheets/Full%20Color%20PDF%20Format/Ergot.pdf

Schuster, J. (2011). Cedar Apple Rust. Retrieved from http://urbanext.illinois.edu/focus/cedarapplerust.cfm

Oklahoma State University. Entomology and Plant Pathology. Retrieved at http://entoplp.okstate.edu/ddd/

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ResourcesUniversity of Illinois. Field Crop Diseases. Retrieved from http://cropdisease.cropsci.illinois.edu/index.html

Stack, R. W. & Lamey, H. A. (November 1995). Deciduous Tree Diseases. Retrieved from http://www.ag.ndsu.edu/pubs/plantsci/hortcrop/pp697-1.htm

Lamey, H. A., Ash, C. L., & Stienstra, W. C. (July 1996). Lawn Diseases. Retrieved from http://www.ag.ndsu.edu/pubs/plantsci/landscap/pp950w.htm#fairy

PAN Germany, OISAT. Retrieved from http://www.oisat.org/pests/diseases/viral.html

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ResourcesMcGrath, M.T. (2004). What are Fungicides. The Plant Health Instructor. Retrieved from ://www.apsnet.org/edcenter/intropp/topics/Pages/Fungicides.aspx

Iowa State University, Entomology Department. Retrieved from http://www.ent.iastate.edu/imagegal/plantpath/

University of Kentucky, Department of Plant Pathology. Retrieved from http://www.ca.uky.edu/agcollege/plantpathology/extension/links.html

Byers, J. A. (2006). Gall-Making Insects. Retrieved from http://www.chemical-ecology.net/insects/gallmake.htm

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