CMG GardenNotes #102 Diagnosing Plant Disorders. Skills Essential to the Diagnostic Process

Transcription

1 CMG GardenNtes #102 Diagnsing Plant Disrders Outline: Skills essential t the diagnstic prcess, page 1 Asking questins, gathering infrmatin, page 2 Steps in the Diagnstic Prcess, page 3 Step 1 Identify the plant, page 3 Step 2 Identify the prblem(s), page 4 Step 2a LOOK Define the prblem by describing the signs and symptms, page 4 Step 2b READ Refer t reference materials describing similar signs and symptms, page 5 Step 2c COMPARE Determine prbable cause(s) thrugh cmparisn and eliminatin, page 5 Step 3 Evaluate if management effrts are warranted, page 6 Step 3a What type f damage/stress des this disrder/pest cause? page 6 Step 3b Under what situatins wuld management effrts be warranted? page 6 Step 3c Are management effrts warranted fr this situatin? page 6 Step 4 Evaluate management ptins effective fr this disrder/pest, page 7 Pesticide use questins, page 7 Skills Essential t the Diagnstic Prcess Judiciusly examine the plant Many gardeners have a difficult time describing their plants and plant prblems. Fr example, the descriptin leaves are yellw is s general that nthing can be diagnsed withut mre details. A typical hme gardener may say they have black bugs. What d they mean by bug? Are they saying they have a black insect? Mre details are needed t diagnse the prblem. Read Part f the diagnstic prcess is t read, cmparing the symptms and signs f the prblems with details in references. D nt simply wrk frm memry. Referring t multiple bks r ther refernces n the same tpic gives a better understanding f a pests descriptin and management situatin. In diagnstic wrk, read fr the details. Ask questins Diagnsis requires extensive tw-way cnversatins. Often the persn trying t diagnse the prblem has nt been n site and has t ttally rely n the descriptins f smene else. In this situatin, diagnsis is difficult t impssible. Even with gd samples r when visiting the site, questins abut the care f the plant, histry f the site and prgressin f symptms are needed in the diagnstic prcess

2 Practice Diagnstics is far mre than applying knwledge that can be read in a bk. The diagnstic prcess requires the integratin f years f gardening wisdm, knwledge and practice. Patience Diagnsing plant disrders is a prcess, nt a simple answer t a questin. It takes time and patience t wrk the prcess. Never jump at an answer just because it seems easy. Dn t guess. Take the time t wrk the prcess, asking lts f questins. In pest management, first diagnse the prblem and then discuss management ptins. Because management ptins are very pest specific, crrect diagnsis f the prblems must be cmpleted befre management can be discussed. Asking Questins and Gathering Infrmatin Ask questins that create dialgue. Fr example, Tell me hw yu watered the plant. Avid accusatry type questins, (e.g., Did yu ver water the plant? ) Sme disrders cannt be diagnsed. We can nly cmplete a diagnsis when detailed infrmatin is available. Descriptins, like yellw leaves r pr grwth are inadequate descriptins fr a diagnsis. Diagnsis must be dne in the cntext f the plant s envirnment. Fr example, is a tree in a rutinely irrigated lawn r in a site with limited irrigatin? Des the site have an pen area fr rt spread r is the rt system limited by pr sils r hardscape features? Fr example, a client calls with cncerns that her tree lks wilted. Shuld she water mre? After asking questins, it is discvered that the tree is lcated in a cnstructin site and had mst f the rt system cut. Understanding the cntext f the rt damage is essential t addressing the watering issue. Questins asked may nt reflect the real issues. - In the diagnstic prcess, Clrad Master Gardener vlunteers must ften help frame questins as well as prvide answers. Fr example, in the previus situatin with the tree in the cnstructin site, an imprtant questin is the stability f the tree with respect t wind as mst f the rts have been cut. A useful tl in diagnsing trees is visualizing the plant, that is creating a mental picture f it and its surrundings. As yu create the picture, ask questins abut details. Verify the details. Explain t the client that yu are trying t create a mental picture f their plant prblem will encurage them t mre patiently prvide the needed infrmatin. When wrking with clients, repeat back their descriptin in yur wn wrds. This helps clear up miscmmunicatins abut symptms. When wrking with clients, verbally explain hw yu rule ut pssible causes. This helps the client mve n with yu and may clarify miscmmunicatin abut symptms. Diagnsis is nt pssible when general symptms are all we have t wrk with. Keep in mind that multiple prblems can have similar symptms

3 Management shuld nly be addressed AFTER the diagnsis is cmplete. Because disrders generally arise frm a cmbinatin f factrs, management must lk at predispsing factrs and inciting factrs in the discussin. Fr details n predispsing, inciting and cntributing factrs (the PIC Cycle) refer t CMG GardenNtes #101, IPM: Plant Health Care). Steps in the Diagnstic Prcess Part A: Diagnsis 1. Identify the plant. 2. Identify the prblem(s). a. LOOK lk at the big picture the site the affected plant is grwing in. b. LOOK at the plant itself including leaves, flwers, fruit, twigs, branches and trunk. c. LOOK fr symptms and signs. d. DEFINE the prblem by describing the symptms and signs. d. OBSERVE the turf r sil the plant is grwing in. Is it difficult t push a screwdriver int the turf r sil? e. ASK questins f. READ Refer t reference materials describing similar signs and symptms. g. COMPARE Determine prbable cause(s) thrugh cmparisn and eliminatin. Part B: Management 3. EVALUATE if management effrts are warranted. a. What type f damage/stress des this disrder/pest cause? b. Under what situatins wuld management be warranted? c. Is management warranted in this situatin? 4. Evaluate management ptins effective fr this disrder/pest and when they are applied. Step 1 Identify the Plant There are hundreds f insects and diseases that attack plants in any gegraphic regin. Once the plant has been crrectly identified, the list f ptential insects and diseases that attack the specific plant drps t just a few. Additinally, insects and diseases accunt fr nly a small percent f landscape plant prblems. When wrking with abitic disrders, plant identificatin will be helpful but will nt shrten the list f ptential pssibilities as significantly. Many gardeners are nt familiar with plant materials and need help t crrectly identify them. Identificatin is nt practical ver the phne. A branch sample with leaves attached shuld be brught t the Extensin ffice r gd phtgraphs 102-3

4 shuld be sent t the diagnstician.(it s really best t see a sample.) Step 2 Identify the Prblem(s) Step 2a LOOK Define the Prblem by Describing the Signs and Symptms. Take a clse lk at the plant and surrundings. A detailed descriptin f the prblem is essential fr diagnsis. In situatins where the descriptin is limited r symptms are t general, diagnsis will be impssible. When diagnsing abitic disrders, systematically evaluating a plant will help rganize questins. Symptms are changes in the plant s grwth r appearance in respnse t causal factrs. Signs are the presence f the actual rganism r direct evidence f the casual factrs. Time develpment Knwing the time frame fr the develpment f signs and symptms is a helpful tl. Did it ccur suddenly r ver a perid f time? Keep in mind that the gardener may nt actually knw as he r she may nt have bserved the early develpment. Symptms that ccur suddenly and d nt prgress are typical f abitic disrders. Symptms that prgressively develp are typical f living factrs (insects and diseases). Keep in mind that multiple prblems have similar symptms. Let the symptms lead yu t the diagnsis rather than trying t make a diagnsis fit a grup f symptms. Terminlgy used t describe cmmn symptms includes: Blight A rapid disclratin and death f twigs, fliage r flwers. Canker Dead area n bark r stem, ften sunken and disclred. Chlrsis Yellwing. Decline Prgressive decrease in plant vigr. Dieback Prgressive death f sht, branch r rt starting at the tip. Gall r gall-like Abnrmal lcalized swelling r enlargement f plant part. It culd be caused by insects, mites, diseases r abitic disrders. Gummsis Exudatin f gum r sap. Leaf distrtin The leaf culd be twisted, cupped, rlled r therwise defrmed. Leaf scrch Brwning alng the leaf margin and int the leaf frm the margin. Leaf spt A spt r lesin n the leaf. Necrsis Dead tissue additinal details are needed. Wilt General wilting f the plant r plant part. Witches brm Abnrmal brm-like grwth f many weak shts. Terminlgy used t describe signs includes: Fruiting bdies Reprductive structures f fungi; culd be in the frm f mushrms, puffballs, pycnidia, rusts r cnks. Insects and mites 102-4

5 Mycelium A mass f fungal threads (hyphae) n the plant surface. Rhizmrphs Shestring-like fungal threads fund under the bark f stressed and dying trees caused by the Armillaria fungi. They may glw! Slime flux r ze A bacterial discharge that zes ut f the plant tissues, may be gey r a dried mass. Examples f abitic (nn-living) signs includes the fllwing: Girdling rts (caused by planting t deep), leads t rt starvatin. Lack f a rt flare (sign that the tree was planted t deep with a high ptential t develp girdling rts). Bark damage n a trunk frm lawn mwers and weed eaters. Standing water ver rting zne. Plugged drip irrigatin system emitters. Recrd f spring time freezing temperatures r severe winter temperatures. Hardscape ver tree rting area. Sil tests indicating high sil salts. Define What Is Nrmal Versus Abnrmal It is cmmn fr the hme gardener t suddenly bserve nrmal characteristics f a tree and mistakenly attribute it t an insect r disease. Fr example, n evergreens: Needle prblems and dieback f the new needles at the branch tip are abnrmal. Yellwing and drpping f lder needles frm the inside f the tree are nrmal in the fall. The number f years that needles are retained is a factr f plant genetics and stress. Under stressful cnditins, needles may drp sner. Other examples f nrmal ccurrences ften cnfused as prblems include: Fuzz n underside f leaves. Male pllen cnes n pine r spruce mistaken fr insects r disease. Less cnspicuus fruit, such as juniper berries. Mushrms. Bluegrass ging t seed. Spres n the underside f fern frnds. Flwers and fruit n ptates (ptat fruit lk like cherry tmates). Tmates drpping blssms after a cl night. Male squash blssms nt prducing fruit. June drp f apples and ther fruit. Aerial rts n tmates and crn Seed stalk n rhubarb and nins

6 Step 2b READ Refer t Reference Materials Describing Similar Signs and Symptms. The reading will ften send yu back t the plant t lk fr mre details. A key in the back f the CSU Extensin publicatin Insects and Diseases f Wdy Plants makes this step easier fr diagnsing insects and diseases f landscape trees and shrubs. Many cmmn abitic prblems are als included. Step 2c COMPARE Determine Prbable Cause(s) Thrugh Cmparisn and Eliminatin. When the descriptin f the disrder matches the details in the reference materials, diagnsis is cmplete. It requires careful reading f fine details. When things d nt match up, back up. Is the plant crrectly identified? Wrk thrugh the prcess again paying attentin t details missed. Let the prcess guide yu thrugh the diagnsis rather than trying t match symptms t fit a diagnsis. Abitic disrders are generally difficult t diagnse. A systematic evaluatin f a plant will be helpful in diagnsing abitic disrders. Abitic disrders ccur in abut 80% f the samples diagnsed by CSU Extensin and ften predispse the plant t insects and diseases. Step 3 Evaluate If Management Effrts Are Warranted Step 3a What Type f Damage/Stress Des This Disrder/Pest Cause? The primary questin here is t determine if the disrder/pest is nly csmetic, if it adds stress t a plant r if it is ptentially life threatening. This may depend, in part, n the verall health f the plant befre the disrder/pest started. Step 3b Under What Situatins Wuld Management Effrts be Warranted? Many insect and disease prblems are nly csmetic n healthy, stress- free plants. Hwever, stressed plants are much less tlerant. Fr example, aphids feeding n shade trees are generally nly csmetic and nrmally d nt warrant management effrts unless they becme a nuisance (like dripping hneydew n a car r pati table). Hwever, under water stress, aphid feeding increases the water needs f the tree creating a ptentially serius stress issue. In this situatin, mechanical (hsing ff the tree with water), binaturals (adding beneficials t feed n the aphids) r insecticidal management effrts wuld be warranted t prtect the tree. As a rule-f-thumb fr leaf chewing insects, healthy trees can tlerate the lss f 1/3 f the ttal leaving surface befre stress becmes a management issue. Tlerance is much less fr trees with grwth limiting factrs. Evergreens are much less tlerant because the needles last fr multiple years. Fr example, a sawfly larva utbreak that remves all the new needles wuld have an influence ver multiple years; this wuld bring a healthy tree t a threshld where management wuld be warranted

7 Step 3c Are Management Effrts Warranted Fr This Situatin? The bttm line in Step 3 is t determine if management effrts are warranted fr this situatin. The answer needs t be fcused n the specifics f this situatin. Step 4 Evaluate Effective Management Optins fr This Disrder/Pest. Management ptins may take many frms r directins. Fr example, hsing ff a plant with a strng frce f water may be an effective mechanical ptin fr sme insect pests. In ther situatins an insecticide may be needed. Management effrts may take the apprach f dealing with sil issues, such as lawn aeratin t reduce sil cmpactin arund a tree. Other management effrts may g in the directin f irrigating a dry site during ht dry weather r reducing ver-watering with better irrigatin system design and management. Management ptins include far mre than just spraying an insecticide. Only fur percent f the insect prblems n landscape trees warrant insecticides. Timing f management effrts is anther imprtant cnsideratin. Often the effective spray windw is past befre the pest is bserved. Pesticide Use Questins When pesticides are a management ptin, answer these imprtant questins t guide pesticide applicatin. 1. What pesticides are effective n this pest? (Refer t Extensin fact sheets.) 2. Which have minimal health risks? (Refer t the pesticide label.) 3. Which have minimal envirnmental risks fr the site? (Refer t the pesticide label.) 4. When are they applied t be effective? (Refer t Extensin fact sheets.) 5. Hw are they applied t minimize health and envirnmental hazards? (Refer t the pesticide label.) 6. What is the re-entry perid and the applicatin-t-harvest interval fllwing applicatin? (Refer t the pesticide label.) Answers t these questins may indicate that a pesticide may r may nt be warranted at the pint in time. Authrs: David Whiting (CSU Extensin, retired) and Carl O Meara (CSU Extensin). Artwrk by David Whiting; used by permissin. Revised June 2017 by Mary Small, CSU Extensin. Clrad Master Gardener GardenNtes are available nline at Clrad Master Gardener training is made pssible, in part, by a grant frm the Clrad Garden Shw, Inc. Clrad State University, U.S. Department f Agriculture and Clrad cunties cperating. Extensin prgrams are available t all withut discriminatin. N endrsement f prducts mentined is intended nr is criticism implied f prducts nt mentined. Cpyright Clrad State University Extensin. All Rights Reserved. CMG GardenNtes may be reprduced, withut change r additins, fr nnprfit educatinal use