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HORT 1003MASTER GARDENER CORE COURSE Horticulture for the Home & Garden

Item # 086112011 Edition

DiagnosticsDiseases, Insects & Other Plant Problems

Item #08611 HORT 1003 Master Gardener Core Course Textbook series

Copyright © 2008, Regents of the University of Minnesota. All rights reserved. Send copyright permission inquiries to: Copyright Coordinator, University of Minnesota Extension, 405 Coffey Hall, 1420 Eckles Avenue, St. Paul, MN 55108-6068. E-mail to [email protected] or fax to: (612) 625-3967.

CreditsEditor / graphic design: Julie WeisenhornProduction coordinator: Linda WasemMaster Gardener Volunteer Manual: David Moen, Julie Weisenhorn, Mary MeyerBotany: Gary Johnson, Cindy TongSoils: Carl Rosen, Peter Bierman, Harlan FinneyHerbaceous Plants: David Zlesak, Mary MeyerWoody Plants: Nancy Rose, Kathy ZuzekTurf: Robert Mugaas, Karyn VidmarWeeds: Robert Mugaas, Karyn Vidmar, Randy NelsonEntomology: Jeffrey HahnPlant Pathology: Michelle GrabowskiDiagnostics: Jeffrey Hahn, Michelle GrabowskiFruits: Emily Hoover, Terry Nennich, Doug Foulk, Karl FoordVegetables: Vince Fritz, Beth JarvisIndoor Plants: Carl Hoffman, Deborah BrownLiving with Wildlife: James Kitts, John Loegering

Thanks to Washington and Virginia Master Gardener Programs for allowing use of information and illustra-tions from their Master Gardener Core Course outlines.

Find more University of Minnesota Extension educational information at http://www.extension.umn.edu/gardeninfo

The information given in this publication is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by University of Minnesota Extension is implied.

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Diagnostics - Hort 1003 Master Gardener Core Course: Horticulture for Home and Garden

Traits of a Good DiagnosticianTraits of a Good Diagnostician

Knowledge of plants, horticulture, soil, Knowledge of plants, horticulture, soil, water, and pest managementwater, and pest management

Access to relevant resourcesAccess to relevant resources

Knowledge of diagnostic techniquesKnowledge of diagnostic techniques

An inquiring, open, logical mindAn inquiring, open, logical mind

Patience and thoroughnessPatience and thoroughness

From Abiotic Disorders of Landscape Plants by Costello et al

DiagnosisDiagnosis

Is a skill, you will improve with practice Is a skill, you will improve with practice and experienceand experience

Not about memorizing a list of problemsNot about memorizing a list of problems

A series of steps taken to identify the A series of steps taken to identify the cause of the problemcause of the problem

Often a process of eliminationOften a process of elimination

What do you do when you What do you do when you encounter a plant with a encounter a plant with a

problem?problem?

www.silentkimbly.com

Diagnostics 1 12/2008


Identify the PlantIdentify the PlantWhat are the common problems What are the common problems of the plant?of the plant?

Know what a normal healthy Know what a normal healthy plant looks likeplant looks like

Pests Have a Host Range Pests Have a Host Range

Broad Broad

Moderate Moderate

Narrow Narrow

JapaneseBeetles

Colorado Potato Beetles

Birch Leafminers

Dutch Elm Disease

Early Blight

Gray Mold

Describe the SymptomsDescribe the Symptoms

Examine the whole plantExamine the whole plant–– Upper & lower surface of leavesUpper & lower surface of leaves

–– BranchesBranches–– TrunkTrunk

–– Fruit & flowersFruit & flowers

What plant parts are affected? What plant parts are affected?

What type of symptoms are present? What type of symptoms are present? What is the pattern of the problem?What is the pattern of the problem?



Look for Signs of the PestLook for Signs of the Pest

Fungal spores, insects, bacterial ooze, Fungal spores, insects, bacterial ooze, insect droppings etc.insect droppings etc.

Will the pests seen cause the damage?Will the pests seen cause the damage?

Tools to Aid Your Tools to Aid Your ExaminationExamination

MagnificationMagnificationAllows you to see Allows you to see Signs betterSigns better

Can show mites, Can show mites, insects, mycelia, insects, mycelia, spores, etc.spores, etc.

Fully examine the Fully examine the plant sample plant sample



Slice it OpenSlice it Open

SuppliesSuppliesRazor Blades or KnifeRazor Blades or KnifeCutting BoardCutting BoardBandBand--aids aids (just in case)(just in case)

www.indigo.com

When to Slice it OpenWhen to Slice it OpenWilt, dieback, marginal Wilt, dieback, marginal necrosis necrosis No visible symptoms on No visible symptoms on branches or trunksbranches or trunksUnknown GallUnknown GallExit holes or Exit holes or FrassFrass Signs & symptomsSigns & symptoms

Discolored veinsDiscolored veinsSclerotiaSclerotiaTunnelingTunnelingInsectsInsects

Consider Timing & Progression Consider Timing & Progression of the Problemof the Problem

When were the symptoms first seen?When were the symptoms first seen?Is the problem spreading?Is the problem spreading?Consider recent and past events. Ask about Consider recent and past events. Ask about –– Pesticide/fertilizer applicationsPesticide/fertilizer applications–– Planting date or age of the plantPlanting date or age of the plant–– ConstructionConstruction–– Weather eventsWeather events



Examine the Surrounding AreaExamine the Surrounding AreaWhat is the pattern of the problem?What is the pattern of the problem?

Is more than one kind of plant affected?Is more than one kind of plant affected?

Consider effects from location of the plantConsider effects from location of the plant–– Soil type / pHSoil type / pH–– Drainage / moistureDrainage / moisture–– Shade / sunShade / sun–– Exposure Exposure –– Nearby buildings, structures, or other objectsNearby buildings, structures, or other objects

What now?What now?Take all of the info you gatheredTake all of the info you gathered

Use references to match signs & symptoms Use references to match signs & symptoms with the specific description of the pestwith the specific description of the pest

References includeReferences include–– BooksBooks

–– Other Master GardenerOther Master Gardener’’s & extension staffs & extension staff

–– Gardening Information WebsiteGardening Information Website

–– Plant Disease Diagnostic ClinicPlant Disease Diagnostic Clinic

Reference Reference BooksBooks

Look for the host plant or suspected pest in Look for the host plant or suspected pest in the the ContentsContents or or Index Index section of the booksection of the book

Try to narrow down the options Try to narrow down the options (fungal, bacterial, galls, chewing damage etc)(fungal, bacterial, galls, chewing damage etc)

Read all remaining options Read all remaining options

Read the symptom description, Read the symptom description, photos can be deceptivephotos can be deceptive



Plant Disease Diagnostic ClinicPlant Disease Diagnostic Clinic

UMN Plant Disease ClinicUMN Plant Disease ClinicSubmit live plant samples to diagnosticianSubmit live plant samples to diagnosticianhttp://pdc.umn.eduhttp://pdc.umn.edu

Charge for servicesCharge for services–– Virus analysisVirus analysis–– Dutch Elm DiseaseDutch Elm Disease–– Oak WiltOak Wilt–– Root rotRoot rot

http://http://www.extension.umn.edu/gardeninfowww.extension.umn.edu/gardeninfo

Jeff HahnJeff HahnInsect QuestionsInsect [email protected]@umn.edu612612--624624--49774977

Michelle GrabowskiMichelle GrabowskiPlant Disease QuestionsPlant Disease [email protected]@umn.edu763763--767767--38763876


www.ext.vt.eduProduced by Communications and Marketing, College of Agriculture and Life Sciences,

Virginia Polytechnic Institute and State University

Virginia Cooperative Extension programs and employment are open to all, regardless of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. An equal opportunity/affirmative action employer. Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Mark A. McCann, Director, Virginia Cooperative Extension, Virginia Tech,

Blacksburg; Alma C. Hobbs, Administrator, 1890 Extension Program, Virginia State, Petersburg.V

Revised 2007 publication 426-714

IntroductionSomething is wrong with your plant. What’s the cause? You can begin to determine the cause of the problem by taking on the role of Sherlock Holmes – be a keen observer and ask many questions. Diagnosing plant problems is often a difficult task. There can be many different causes for a given symptom, not all of them related to insects or diseases. The health of a plant may be affected by soil nutrition and texture, weather condi-tions, quantity of light, other environmental and cultural conditions, and animals, including humans. Complicat-ing this scenario is the fact that any two of the above factors can interact to give rise to a problem. For exam-ple, a prolonged period of drought may weaken plants so that they are more susceptible to pests; this is typi-cally observed with boxwoods.

The most effective approach is to know what questions to ask to narrow down the possibilities. For example, you need to consider recent rainfall and the fertiliza-tion schedule if you notice brown, dry edges on the leaves of your plants since both dry weather and excess fertilizer can cause such damage. In another example, either excessively dry soil or waterlogged soil can cause the same plant reaction: wilt. Even insect damage can sometimes be confused with plant diseases caused by microorganisms.

First Questions to AskTo determine what is wrong with a plant, one should first investigate the history of the plant. These questions will help you narrow down the cause of the problem:

Q: How long has the plant been in its cur-rent location?A: If the plant has been transplanted recently, the prob-

lem may be associated with the transplanting oper-ation or post-transplant conditions. You will also want to find out if the plant was planted as a con-tainer-grown plant or a ball and burlap (B&B) plant. A recently transplanted container-grown plant will require frequent irrigation during the warm portions of the year. Thus, poor health may be related to the need for water. In the case of a B&B plant, poor health may be related to the shock of root severance, species-related reaction to the B&B harvest, or the time of harvesting or planting.

Plants that have been recently transplanted are not “established.” Being established implies that there has been appreciable root growth from the root ball into the adjacent soil. When the plant is not established, it relies solely on the relatively limited water supply available in the root ball. Being estab-lished also implies that the plant has acclimated to the above and below ground environmental condi-tions. Such conditions are in direct contrast to those relatively “lush” conditions of a production nursery. Plants that are not established are reliant on fre-quent irrigation and are less cold hardy than estab-lished plants. While there are no data to support this hardiness contention, I have noticed this phe-nomenon and over the years have had fellow plant people agree with this observation. Thus, a recently transplanted plant may be affected by low winter temperatures while a nearby established plant of the same species may be undamaged.

Diagnosing Plant ProblemsAlex X. Niemiera, Associate Professor and Extension Specialist, Department of

Horticulture, Virginia Tech

Diagnostics 12/2008

Q: What has been done to the plant or near the plant?A: Has any construction, spraying, fertilizing, or

any other operation taken place in the past? I was once asked about the demise of a relatively large yew plant in a neighbor’s garden. The plant was unthrifty and I asked about the history, but noth-ing significant was reported. Soil and plant analy-sis did not yield any clues. However, after digging around the plant, it was determined that roots were not getting enough oxygen because three years ago excavated soil from a nearby water garden project was dumped on top of the soil around the yew. The dead needle/branch symptoms were slow to develop and these symptoms were not associated with soil being piled onto the root system. In this case, the reason for plant damage was a lack of oxygen sup-ply to roots, but the true cause and culprit was the homeowner. Thus, try to find out about anything that was done in the vicinity of the plant in ques-tion in the year or years prior to the appearance of symptoms.

Q: What are or were the prevailing weath-er conditions?A: In many cases uncharacteristically warm, cold,

dry, or wet weather can result in plant problems. Unusually warm spells in the spring followed by very low temperatures can damage or kill many plants. Plants that leaf out early such as Japanese maples are most vulnerable. In some cases, unusu-ally mild weather during the fall will promote lush growth that has not hardened off and therefore has not started to acclimatize to low temperature condi-tions. This lush foliage will then be damaged by the first exposure to relatively low temperatures. Rela-tively fast-growing plants and those that have an indeterminate growth habit (shoot growth continues through the growing season) are especially prone to such cold damage. Unusually dry weather in any season will bring on drought symptoms (wilting, leaf and branch death). But there may be an interaction of weather conditions and season. Years ago, there was an especially dry fall and winter which resulted in significant damage to landscape and field-grown (nursery-produced) broadleaved evergreens. Thus, evergreen plants such as southern magnolia and boxwood, species which transpire (lose water vapor from leaves) during most of the year, were severely

damaged due to the interacting conditions of low soil moisture and low winter temperatures/dry air.

Causes of Plant DamageFactors causing plant damage can be grouped into two major categories, living and nonliving factors. Living factors include pests (e.g., insects, mites, rodents, rab-bits, deer, humans) and pathogens (e.g., disease-caus-ing microorganisms, including fungi, bacteria, viruses, nematodes). Nonliving factors include mechanical fac-tors (e.g., breakage, abrasions), environmental factors (e.g., temperature, light, moisture, oxygen, lightning, wind), and chemical factors (e.g., fertilizer or pesticide excess, nutritional disorders).

Use a Systematic ApproachDefine the problem. Closely examine the entire plant and others around it. Take note of all the symptoms. For example, if the plant has insects, examine the leaves with insects on them; do they have brown spots, holes, chewed edges? Are they turning pale green or yellow? Is there more than one kind of insect present?

Look for patterns. Do other plants have the same problem? Are they all in the same place or in different loca-tions? Are they all the same type of plant? Damage to all different types

of plants in a particular spot can indicate nonliving fac-tors. Damage to a few species of plants or only to plants of the same species can indicate living factors.

Observe where the damage occurs on a plant. Are the symptoms exhibited throughout the plant or are they localized? For example, when the tops of plants wilt or die, one can generally infer that there is a problem with the root system. When the root systems of shrubs and trees are adversely affected by either too much or too little water, soil compaction, or root damage from con-struction activities, the damage generally shows up in the top or growing points.

Examine the spread of the problem. Is the problem spreading gradually? This can indicate living factors. If the problem occurred suddenly and remains in a par-ticular spot or on a particular plant, this points toward nonliving factors. There are, however, diseases that can kill a plant within a short period of time, although this is not common.


Determine likely cause of damage. Based on the pat-tern and spread, decide if the problem is more likely caused by living factors or nonliving factors. If living, is the problem a pathogen or a pest?

Living FactorsIf disease is a possibility, check the following general guidelines for identifying the different causes of disease:

A fungal pathogen often causes round leaf spots, stem rots with a dry/papery texture, concentric rings, discoloration, or wilt. Fruiting structures (sometimes microscopic) may form on affected tissue.

A bacterial disease can take the form of galls (swollen areas), irregu-larly shaped leaf spots, wilting (then yellowing and dying), or rot (often a wet rot).

A viral pathogen can inhibit chlorophyll formation, causing degrees of yellowing or mottling, stunting, dis-tortion, or dieback of part of the plant. Viruses usually debilitate rather than kill, as they are parasitic.

Nematodes are microscopic roundworms that cause disease-like symptoms. Stem nematodes feed on stems and cause shortening of internodes. Root nematodes feed underground, damaging the root system; this leads to moisture and nutrient stress which shows up as wilt-ing and stunting. Foliar nematodes cause angular leaf spots.

If an insect problem seems likely, check the following: A chewing/rasping insect feeds on plant tissue and can cause ragged/chewed or missing leaves (e.g., caterpillars, slugs, beetles, grasshoppers), rolled leaves (leafroller), tunnels in between upper and lower leaf surfaces (leaf miners). They can also cause holes in stems, branches or trunk, sections of tree dying, or premature yellowing (wood borers); girdled or dead stems (cutworms, twig girdlers, or stem borers); or general decline of plants due to root damage (soil-dwelling insects)

A sucking insect feeds on plant fluids and injects toxins into the plant. The toxins can cause leaf spot-ting or stippling (e.g., aphids, leafhoppers, spider mites), leaf distortion such as curling or puckering (or more commonly this can be damage from leafhop-pers and thrips), or poisoning of entire plants, resulting in stunted growth and/or yellowing (e.g., scale, mealybugs, mites, aphids, whitefly).

Nonliving FactorsDamage caused by mechanical factors is usually revealed by close visual examination; check for broken or girdled stems or roots, also bruised, punctured, or broken leaves. Damage to the base of a tree trunk is often caused by weed trimmer or mower damage.

Damage due to physical factors often results from environmental extremes. Cold damage is character-ized by death of exposed foliage. Container plants are susceptible to cold damage to the root system, charac-terized by blackened or spongy roots with lack of new growth or root hairs, usually near the container edge.

A rapid change from low light to high light intensity, or vice versa, can cause yellowing of leaves, reduced growth, and leaf drop or death. Too little light can reduce, delay, or prevent flowering and will also result in very lanky, sparse growth.

Excess heat usually causes scorch symptoms on leaf tips and interveinal areas. Portions of leaves shaded by other leaves, or leaves on the shady side of the plant, may be undamaged. Frequently, heat damage will occur uniformly over all plants in an affected area.

Drought and waterlogging produce many of the same symptoms on the aboveground parts of the plant, mainly chlorosis (yellowing leaves), abscission (shedding older leaves), and wilt. Waterlogging of the root zone also results in oxygen deficiency, leading to a halt in root growth and metabolism, death of the roots, and wilt.

Damage due to chemical factors, inappropriately used pesticides or excessive rates of pesticides, can cause symptoms, such as leaf burn, distortion, chlorosis, or


bleaching, depending on the chemical. On a field basis, pesticide or fertilizer damage symptoms frequently are associated with application patterns.

Nutrient deficiencies show up as yellowing, stunting, or death of older plant leaves or new growth, depending on the missing nutrients.

Refer to expert information. Talk to your Extension agent or to local garden center personnel, explaining the symptoms thoroughly, or check all the symptoms against a good chart or reference book, keeping in mind the factor you have determined as the likely cause. If it appears insects or pathogens are causing the problem, be sure to positively identify the pest so you can choose the most effective control measure.

Double-check the ObviousIt never hurts to look again for obvious problems. Is the stem/trunk badly damaged? Has the plant been sit-ting in a saucer of water for a week? Has your neighbor sprayed an herbicide lately? Does your cat enjoy fern salad? Is your dog deprived of fire hydrants? Do your children “help” you by cleaning the plants with furni-ture polish or window cleaner?

For more information on plant selection, planting, cul-tural practices, and environmental quality, contact your local Virginia Cooperative Extension office. If you want to learn more about horticulture through train-ing and volunteer work, ask your Extension agent about becoming a Master Gardener. For monthly gardening information, subscribe to The Virginia Gardener News-letter by sending your name and address and a check for $5.00 made out to “Treasurer, Virginia Tech” to The Virginia Gardener, Department of Horticulture (0349), Virginia Tech, Blacksburg, VA 24061. Horticultural information is also available at Virginia Cooperative Extension’s website, www.ext.vt.edu.

This publication was originally authored by Diane Relf, Extension Specialist (ret.), Environmental Hor-ticulture, Virginia Tech, and the original development of this series was funded by ESUSDA Smith Lever 3(d) National Water Quality Initiative Funds and the Virginia Department of Conservation and Recreation, Division of Soil and Water Conservation.


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