CMG GardenNotes #331 Plant Pathology

Transcription

1 CMG GardenNtes #331 Plant Pathlgy Outline: Intrductin, page 1 Plant disease pyramid, page 2 Symptms, page 2 Signs, page 3 Bitic Diseases, page 3 Fungi, page 3 Damping ff, page 4 Leaf spts, page 4 Mildew, page 5 Cankers, page 6 Rt rts, page 6 Bacteria, page 7 Viruses, page 8 Phytplasmas, page 9 Aster yellws, page 9 Parasitic Plants, page 10 Nematdes, page 10 General management f bitic plant diseases, page 11 Abitic disrders, page 12 Water management, page 12 Leaf scrch, page 13 Oxygen starvatin, page 13 Weather, page 14 Temperature, page 14 Chemical injury, page 15 Herbicides, page 15 Fertilizers, page 16 De-icing salts, page 16 Plant diseases diagnsis, page 17 Sample questins, page 18 Identify the plant and its nrmal characteristics, page 19 Identify pattern f plant damage, page 19 Distinguish between bitic and abitic factrs, page 19 Intrductin A plant disease is usually defined as abnrmal grwth and/r dysfunctin f a plant. Diseases are the result f sme disturbance in the nrmal life prcess f the plant. Diseases may be the result f living and/r nn-living causes. Bitic diseases are caused by living rganisms (e.g., fungi, bacteria, and viruses). Abitic diseases are caused by nn-living envirnmental cnditins, (e.g., sil cmpactin, wind, frst, sil salt damage, and girdling rts)

2 Plant Disease Pyramid Specific cnditins must be present fr bitic disease t develp. There must be a susceptible hst plant, the pathgen (fungi, bacteria, viruses, etc.), and envirnmental cnditins cnducive t disease develpment; these must cme tgether in a given pint in time. These cnditins make up what is called the Plant Disease Pyramid. Bitic disease cannt ccur if ne f these pieces is missing. [Figure 1] Envirnmental Cnditins Weather plays a large rle in fungal disease develpment. Mst fungi require free water r specific levels f humidity r misture fr prlnged perids f time t develp. Dry climates are nt cnducive t their survival. The Rcky Muntain regin has fewer fungal diseases than many ther parts f the United States due t climatic differences. Hwever, gardens and ther micrclimates may have cnditins ideal fr disease develpment due t pr air circulatin, shade, high humidity, and high misture. Figure 1. Plant Disease Pyramid Symptms Symptms f disease are the plant s reactin t the causal agent. Plant symptms include: Blight A rapid disclratin and death f twigs, fliage, r flwers. Canker Dead area n bark r stem, ften sunken r raised. Chlrsis Yellwing Chlrsis is s generic that withut additinal details diagnsis is impssible. Decline Prgressive decrease in plant vigr. Dieback Prgressive death f sht, branch, r rt starting at the tip. Distrtin Malfrmed plant tissue 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 Burning alng the leaf margin and int the leaf frm the margin. Leaf spt A spt r lesin n the leaf. Msaic Varying patterns f light and dark plant tissue Necrsis Dead tissue Necrtic areas are als s generic that withut additinal details diagnsis is impssible. Stunting Lack f grwth Wilt General wilting f the plant r plant part. Witches brm Abnrmal brm-like grwth f many weak shts. Insect feeding injury is als a symptm used in diagnsis, but nt a symptm f disease

3 Even thugh a plant has symptms n a specific part, it des nt necessarily mean the damaged tissue cntains the rganism causing the symptms. Fr example, a rt rt can cause chlrsis and wilting f stems and leaves, but the disease causal rganism is in the rts. It is imperative t examine as much f the plant as pssible t determine exactly where the prblem is riginating. Signs Signs are the actual rganisms causing the disease. Signs include: Cnks Wdy reprductive structures f fungi Fruiting bdies Reprductive structures f fungi; culd be in the frm f mushrms, puffballs, pycnidia, rusts, r cnks. Mildew Whitish grwth prduced by fungi, cmpsed f mycelium Mushrms Fleshy reprductive structures f fungi Mycelium Thread-like vegetative grwth f fungi. 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 Oze A bacterial discharge that zes ut f the plant tissues, may be gey r a dried mass. Spre masses Masses f spres, the seeds f a fungus Insects and/r their frass (excrement) are als signs, althugh nt signs f disease. Bitic Disease Bitic causes f disease include fungi, bacteria, viruses, phytplasmas, nematdes, and parasitic plants. Fungi Fungi are rganisms that are classified in the kingdm Fungi. They lack chlrphyll and cnductive tissue. Until a few years ag, fungi were cnsidered lwer frms f plants, but tday are classified as a grup by themselves. Because fungi cannt manufacture their wn fd (due t lack f chlrphyll), they must btain it frm anther surce as either a saprphyte r parasite. Mst fungi encuntered are saprphytic (feed n decaying rganic matter). The parasitic fungi, thse that derive their sustenance frm living plants, are the grup f interest in plant health. In dry climates like Clrad, fungi are the mst frequent causes f plant diseases. A fungus bdy is a branched filamentus structure knwn as mycelium. One single thread is called a hypha (hyphae, plural). Mst fungi reprduce by spres, which are structures that cntain little stred fd (unlike seed). Spres are the main dispersal mechanism f fungi and can remain drmant until germinatin cnditins are apprpriate. Many fungi ver-winter as fruiting structures embedded in dead plant tissue. When a spre cmes int cntact with a susceptible plant, it will germinate and enter the hst if the prper envirnmental cnditins are present. Hyphae develp frm the germinated spre and begin t extract nutrients frm hst plant cells. The hyphae secrete enzymes t aid in the breakdwn f rganic materials that are 331-3

4 ultimately absrbed thrugh their cell walls. Fungi damage plants by killing cells and/r causing plant stress. Fungi are spread by wind, water, sil, animals, equipment, and in plant material. They enter plants thrugh natural penings such as stmata and lenticels and thrugh wunds frm pruning, hail, and ther mechanical damage. Fungi can als prduce enzymes that break dwn the cuticle (the uter prtective cvering f plants). Fungi cause a variety f symptms including leaf spts, leaf curling, galls, rts, wilts, cankers, and stem and rt rts. Fungi are respnsible fr damping ff symptms assciated with seedlings. Damping Off Damping ff is the fungal infectin f seeds r seedlings that leads t death. When infected with damping ff, seeds may fail t germinate. In ther situatins, seedlings develp but eventually fall ver and die. An examinatin f stems at the sil line reveals a disclred, pinched in appearance. Mst plants are susceptible t damping ff because f the sft immature nature f seedling tissue that is mre susceptible t infectin. The best methd t manage damping ff is t avid it in the first place. Fr starting seeds indrs, use pasteurized sil r planting mix and ensure that plants receive ptimum light, water, and heat fr rapid germinatin and grwth. In hme situatins, damping ff frequently develps due t pr lighting and verwatering. These cnditins stress plants and make cnditins ptimal fr the develpment f the sil-brne rganisms that cause damping ff. In the garden, plant seeds at apprpriate times (crrect sil temperature fr rapid germinatin) fr the crp and avid verwatering fr ptimal germinatin and grwth. A strng healthy plant is better equipped t fight ff infectin. Scientists cntinue t study the rle f hyperparasites (parasites f parasites) in disease management. Several bilgical pesticides have been develped frm naturally ccurring hyperparasitic fungi and bacteria. The rganisms prtect plant rts against invasin by harmful sil pathgens. These bilgical pesticides must be applied prir t the develpment f damping ff s the beneficial rganisms have time t grw and clnize rts. They cannt be used as rescue treatments. Leaf Spts One f the mst cmmn fungal plant symptms is leaf sptting. Leaf spt symptms are caused by many different fungi. Generally, fungal leaf spts pssess a distinct dark brwn r red margin between the interir (dead) and exterir (healthy green) tissue called a brder r margin. (Figure 2). Fungal fruiting structures (reprductive structures) are usually embedded in the dead interir. Frequently, a hal f yellw r red clr develps arund the brder. A hal indicates recently killed tissue that will eventually die. Because f the cycle f killing tissue and creating a brder, then killing mre tissue and creating anther brder, many fungal leaf spts take n a target-like appearance

5 T cnfuse matters, a series f drught events can cause damage that exhibits alternating light and dark bands. Additinally, fruiting structures may nt be bvius in dry climates like Clrad. T psitively identify a fungal leaf spt, it is best t either culture tissue frm the sample r lk fr spres under a cmpund micrscpe. Examples f cmmn leaf spt diseases in Clrad include Marssnia and Septria leaf Figure 2. Cedar knt gall rust is a cmmn leaf spt with a clrful brder. spts f cttnwds and aspen, ink spt f aspen, and early blight f tmates and ptates. Fr additinal infrmatin, refer t the fllwing Clrad State University Extensin publicatins available nline at Aspen and Pplar Leaf Spts, Extensin fact sheet #2.901 Aspen Leaf Spt, Planttalk #1403 Marssnina Leaf Spt Planttalk #1476 Sycamre Anthracnse, Extensin fact sheet #2.930 Sycamre Anthracnse, PlantTalk #1406 Pwdery Mildew Pwdery mildew is ne f the mst cmmn diseases in dry climates like Clrad. General symptms include a white r grayish pwdery grwth n leaves. It thrives in warm dry climates, ften expldes in small yards with limited air mvement, and in the fall as nighttime humidity rises. [Figure 3] Figure 3. Pwdery Mildew There are many species f mildew fungi, each being hst-specific. In Clrad, fr example, it is cmmn n ash, lilac, grapes, rses, turfgrass, vine crps (cucumbers, melns, and squash), peas, eunymus, cherry, apple, crabapple, pear, Virginia creeper, and thers. Management is centered n a variety f cultural techniques. Avid crwding plants as the lack f air circulatin favrs pwdery mildew. Select resistant varieties where pssible. Avid late-summer applicatin f nitrgen fertilizer as it may push grwth f tender yung leaves that are mre prne t mildew. Avid 331-5

6 verhead irrigatin as it raises relative humidity. Remve and destry infected plant parts. A variety f fungicides fund in the hme garden trades are effective against pwdery mildew. Fr additinal infrmatin, refer t Clrad State University Extensin fact sheet #2.902, Pwdery Mildew, available nline at Cankers Cankers are disclred, sunken areas fund n plant stems, branches, and trunks. They damage plants by killing the cnductive tissue and girdling the plant. Cankers may be caused by fungi, bacteria, virus, and abitic disrders such as sunscald and hail (Figure 4). Fungal cankers cntain fruiting Figure 4. Canker at base f structures embedded in the hneylcust disclred canker. Plants with cankers may exhibit branch dieback, leaf lss, and/r pr grwth abve the damaged area. Cmmn fungal cankers in Clrad are Cytspra (Cytspra sp.) and Thyrnectria (Thyrnectria sp.). Cmmn bacterial cankers in Clrad include fireblight (Erwinia amylvra). Fr additinal infrmatin, refer t the fllwing Clrad State University Extensin publicatins available nline at Canker Diseases n Deciduus Trees, PlantTalk #1407 Cytspra Canker, Extensin fact sheet #2.937 Cytspra Planttalk #1451 Canker Diseases n Deciduus Trees Planttalk #1407 Fire Blight Extensin fact sheet #2.907 Fire Blight Planttalk #1411 Hneylcust Diseases fact sheet #2.939 Rt Rts Rt rts damage plants by stressing r killing rt systems. Tw cmmn silinhabiting fungi that cause rt rts include Fusarium sp. and Rhizctnia sp. Rt symptms f these (and ther sil-brne) fungi include darkening, limpness, and mushiness. Rtted rts may break ff easily. The crtex (the uter prtective cvering) f rts slughs ff, leaving behind the thread-like rt cre. Leaves, stems, and entire plants may wilt, prmpting ne t think that the plant simply needs mre water. (Unfrtunately, additinal water ften makes the prblem wrse.) 331-6

7 Generally, the lwer, interir leaves turn yellw, then brwn and drp ff. In additin, plants may be stunted. If enugh rts are damaged, the plant eventually dies. There are n rt-rt resistant plants. Management strategies include aviding verwatering and imprving sil drainage. Rts stressed frm verwatering r xygen starvatin easily succumb t rt rts, because the rganisms mve thrugh mist sil and water. Smetimes, a plant with rt rt may be salvaged by cutting ff damaged rts and replanting in well-drained sil. Bilgical pesticides cntaining hyperparasites may help prtect against rt rt. These prducts are nt designed t rescue plants frm nging damage, but act as preventives. In the Green Industry, rt rts can be managed with a cmbinatin f the cultural management strategies and thrugh use f fungicides. Because nt all fungicides kill all rt rt fungi, it is essential t determine which rt rt rganism is causing the prblem thrugh micrscpic examinatin s the crrect prduct can be recmmended. Bacteria Bacteria are single-celled micrrganisms. They cntain n nucleus and reprduce by dividing int tw equal parts (fissin). As a result, they multiply and mutate rapidly. Bacteria functin as either parasites r saprphytes. Bacteria can infect all plant parts. Unlike fungi, bacteria must find a natural pening fr entry. Bacterial cells can mve frm ne plant t anther in water, sil, and plant material, just as fungi d. Hwever, bacterial pathgens are mre dependent n water. Cnditins must be very wet and/r humid fr them t cause significant and widespread damage (Figure 5). Bacteria mve between plant cells and secrete substances that degrade plant cell walls s the cntents can be utilized. Sme prduce enzymes that break dwn plant tissue, creating sft rts r water-saking. Like the fungi, bacteria cause symptms such as leaf blights and spts, galls, cankers, wilts, and stem rts. Bacterial leaf spts appear different frm fungal leaf spts due t their intercellular mvement. Veins ften limit the develpment f a lesin, s they appear angular r irregular, nt rund. Figure 5. Fireblight n crabapple Bacterial diseases are nt cmmn in the Rcky Muntain regin due t lack f natural misture

8 It is difficult fr beginners t tell fungal and bacterial plant symptms apart. Table 1 may be used t help distinguish symptms caused by these pathgens. Table 1. Cmparisn f Fungal and Bacterial Leaf Spts Symptm Descriptin Fungal Bacterial Water-saked appearance N Yes Texture Dry, papery Slimy, sticky Smell N Yes Pattern Circular, target-like Irregular, angular Disintegratin N Yes Clr changes Red, yellw, purple hals N Structures f pathgen Mycelia, spres, fruiting structures N Cmmn bacterial diseases in Clrad include bacterial wetwd (slime flux), fireblight (Erwinia amylvra), and bacterial leaf spt (Erwinia sp.). Fr additinal infrmatin, refer t the fllwing Clrad State University Extensin publicatins available nline at Bacterial Wetwd Extensin fact sheet #2.910 Bacterial Wetwd Planttalk #1438 Fire Blight Extensin fact sheet #2.907 Fire Blight Planttalk #1411 Viruses Viruses are crystalline particles cmpsed f nucleic acid (ribnucleic acid r dexyribnucleic acid) and prtein. They are bligate parasites, meaning they are unable t survive utside f their hst. Small virus particles can be fund in all plant parts and cannt be seen withut an electrn micrscpe. T mve frm plant t plant, the particles must be transmitted by vectrs and thrugh a wund. The vectr is typically an insect, nematde, r human. Insects and nematdes spread viruses between plants as they feed n them. The feeding injury creates the necessary wund. Usually, a plant virus is spread by nly ne kind f insect vectr. Aphids, leafhppers, and thrips are examples f virus vectrs, but nt all aphids, leafhppers, r thrips spread virus. Humans may spread plant viruses as they wrk in the garden. Mechanical abrasin frm infected tls r tuching and abrading plants with infected hands may be all that is needed. Viruses verwinter in infected perennial plants r verwintering insects. A small prtin f viruses can be transmitted thrugh seeds. Sme are transmitted thrugh vegetative prpagatin

9 Viruses cause mttling, spts, msaic-like patterns, crinkling, and ther malfrmatins n leaves and fruits, and may stunt plants. Because viruses are systemic, infected plants must be rgued r discarded (Figure 6). Viruses are named accrding t the first plant n which they were fund and the type f symptm they cause (i.e., peny ringspt virus, rse msaic virus). Fr example, cmmn virus diseases in Clrad include curly tp virus f tmates, cucumber msaic virus f vine crps and tmates, tmat sptted wilt virus f tmat, and a variety f greenhuse plant viruses. Fr additinal infrmatin, refer t the fllwing Clrad State University Extensin publicatins available nline at Fig. 6. Tmat sptted wilt virus n tmat fruit Greenhuse Plant Viruses, Extensin fact sheet #2.947 Recgnizing Tmat Prblems, Extensin fact sheet #2.949 Phytplasmas Phytplasmas are bacteria-like rganisms; hwever, they lack a cell wall and can take n a variety f shapes. They are bligate parasites, meaning they can nly survive within their hsts. Phytplasmas live in the phlem f hst plants and are vectred by certain phlem-feeding insects, such as leafhppers. This pathgen causes distrtin, yellwing, wilting, and witches brms (a prliferatin f grwth). Immature leaf veins may appear clear (called vein-clearing ). Flwer parts may becme vegetative and flwers that d develp prduce sterile seeds. Aster Yellws Aster yellws damages ver 300 species f bradleafed herbaceus plants natinwide. Cmmnly affected flwering plants include Echinacea sp. (purple cneflwer), csms, mariglds, asters, chrysanthemums, delphiniums, daisies, crepsis, and zinnias. Vegetables affected Fig 7. Aster yellws n carrt include carrts, lettuce, and ptates. Weeds such as dandelin, ragweed, plantain, wild lettuce, and thistles may als be infected (Figure 7)

10 Aster yellws is spread by the aster (r six-sptted) leafhpper. These insects are small (ne-eighth inch lng), gray-green, and wedge-shaped. They are called leafhppers because they mve r fly away quickly when plants are disturbed. They feed nly n plant sap (phlem tissue) and generally n leaf undersides. Aster leafhppers d nt verwinter in Clrad due t the cld climate, but are blwn in frm the Gulf f Mexic in late spring r early summer. Once a leafhpper feeds n an infected plant, abut 10 days t 3 weeks must elapse fr the insect t becme infective. Plant symptms appear 10 t 40 days after infectin. Dry weather can cause increased disease ccurrence in the hme garden as leafhppers mve frm plants in prairies and pastures t irrigated yards. Generally, aster yellws symptms appear in middle t late summer. Althugh aster leafhppers spread the disease, placing infected plants in the yard can als spread it. Management strategies fr aster yellws include planting healthy plants, cntrlling weeds that may harbr the insects, and remving infected plants. Even thugh nly ne part f a plant appears infected, ne must assume the phytplasma is thrughut the entire plant. The pathgen can verwinter in plant crwns and rts. Leaves and stems that develp frm this tissue will always be infected and prvide a surce f inculum fr ther susceptible plants. Insecticidal cntrl f aster leafhppers is very difficult as they are cnstantly mving in and ut f the garden, s it is nt recmmended. Fr additinal infrmatin, refer t Clrad State University Extensin PlantTalk script #1452, Aster Yellws, available nline at Parasitic Plants Mre than 2,500 species f higher plants are knwn t live parasitically n ther plants. Parasitic plants prduce flwers and reprduce by seeds like ther plants. The main difference is they cannt prduce their wn chlrphyll r prduce nly a small amunt f chlrphyll. They must btain sustenance frm a chlrphyllprducing plant t survive. Parasitic plants are spread in varius ways including animals, wind, and frcible ejectin f their seeds. Dwarf mistlete and ddder are tw examples f parasitic plants encuntered in Clrad. Dwarf mistlete has chlrphyll but n rts and depends n its hst fr water and minerals, althugh it can prduce carbhydrates in its green stems and leaves. Ddder cannt prduce its wn chlrphyll and cmpletely depends n its hst fr sustenance. Plants damaged by parasitic plants appear wilted, stunted, distrted, and chlrtic. Sme plants, particularly cnifers, develp witches brm symptms. Fr additinal infrmatin, refer t the Clrad State University Extensin fact sheet #2.925, Mistlete in Clrad Cnifers, available nline at

11 Nematdes Nematdes are micrscpic rundwrms that live in sil, water, and plant material. They have a spear-like stylet muthpart, require free water t mve abut, and reprduce by eggs. They spread in water, infected plant material, sil, and in sme cases, insects. Nematdes cause a variety f symptms including stunting, yellwing, and wilting f plant tissue. Sme infected plants simply appear unthrifty. Sme develp strange, knt-like grwths n their rts. Many saprphytic and parasitic species exist. Due t cld winters, nematdes as plant pathgens are uncmmn prblems in Clrad landscape plantings. Pinewd nematde (Bursaphelenchus xylphilus) is a Nrth American native nematde that invades extic pines such as Austrian, black, and Scts pines. Pinewd nematde causes pine wilt disease. The symptms include needle necrsis, branch flagging, and eventual tree death. Trees may decline rapidly; whle tree death can ccur in 2 weeks. Pinewd nematdes are vectred tw ways. The primary transmissin is by maturatin feeding f adult pine sawyer beetles (Mnchamus sp.) n susceptible trees. Secndary transmissin ccurs when adult female pine sawyer beetles vipsit (lay eggs) int phlem f susceptible trees. If this disease is suspected as the cause f pine tree death, samples must be sent t a diagnstic labratry t accurately diagnse pine wilt disease. Fliar nematdes are fund ccasinally in irrigated Clrad landscapes. They have a brad hst range and can infect many plant species but especially anemne and chrysanthemum. General Management f Bitic Plant Disease Plant disease is best managed thrugh an integrated apprach, which includes a cmbinatin f cultural, mechanical, bilgical, and chemical practices. Cultural management includes apprpriate plant selectin. Utilize plants that perfrm well in the lcal climate. Use disease-resistant varieties when pssible. Plant certified seed r seed pieces. Place plants in the apprpriate envirnment fr ptimum grwth. Fr example, grw shade-lving plants in the shade, nt ht sun. Prepare sil befre planting t imprve rt grwth, reduce cmpactin in clay sils, and imprve water hlding f sandy sils. Apply fertilizer and water accrding t plant needs. Prune crrectly, as needed, and at the crrect time f year. Mechanical management techniques include rttilling in the fall, which expses pathgens, insect eggs, and weed seeds t cld winter temperatures. This actin als speeds the decmpsitin f crp residues, imprving sil rganic matter. Clean up r prune ut infested plant materials t reduce the surce f inculum n the prperty

12 Rtate crps when pssible t starve pathgens. Fr example, avid planting slanaceus crps in the same area as pathgens specific t this grup may build up in sil and infect new crps. Apply mulch in gardens. Nt nly des this keep sil mister and cler (helping rts thrive), it als creates a splash barrier against sil pathgens r pathgens n plant debris in the sil. Use sil slarizatin t reduce sil pathgens and weed seeds. Pull weeds and vlunteer seedlings that hg precius water but als serve as a reservir fr pathgens and insects. Cre-aerate turf nce r twice yearly. Bilgical cntrls include the use f cmpst, cmpst teas, and hyperparasite prducts, which may reduce pathgens by intrducing beneficial micrbes. Encurage beneficial insects by planting flwering plants attractive t all stages f develpment. Avid blanket applicatins f pesticides, which may kill beneficials in additin t harmful insects. Spt treat pest prblems instead. Chemical cntrl refers t the use f fungicides, insecticides, and herbicides t manage a prblem. Always identify the cause f a plant prblem first, then select and use a prduct apprpriate fr the prblem and fllw label directins. Apply it at the crrect time using the recmmended methd. Always spt treat. Abitic Disrders Abitic agents f disease are nn-living factrs such as sil cmpactin, spring frsts, hail, and lawnmwer damage t tree trunks. Abitic agents are nninfectius and nn-transmissible. Plant diseases deriving frm these agents have been referred t as physilgical diseases r envirnmental diseases. Fr additinal infrmatin, refer t the fllwing Clrad State University Extensin publicatins, available nline at Diagnsing Rt and Sil Disrders f Landscape Trees, Clrad Master Gardener GardenNtes #103 Envirnmental Disrders f Wdy Plants, Extensin fact sheet#2.932 Healthy Rts and Healthy Trees, Extensin fact sheet #2.926 Water Management One f the majr causes f abitic plant disrders is imprper water applicatin. T much water can be just as damaging as nt enugh water, as bth kill rts. Examples f abitic disrders related t water are leaf scrch, winter desiccatin, and xygen starvatin (Figure 8). Figure 8. Water stress n trees ften appears frm the tp dwn

13 Leaf Scrch Symptms f leaf scrch include necrsis (brwning) f leaf edges and/r between the veins. These are naturally the least hydrated areas f a deciduus leaf, s when misture is lst, symptms appear there first. Scrch symptms n needled evergreens appear as necrsis frm the needle tips dwnward in a unifrm pattern. The initial reactin t these symptms is t prvide mre water, but that may nly exacerbate the situatin depending n what is causing scrch in the first place (Figure 9). There are several causes f leaf scrch. There may nt be enugh water in the sil fr rt absrptin. This ccurs during drught perids as Clrad experienced in the early 2000s and during winters when sil water is frzen. Water may be lst faster than it can be replaced. Warm, windy, and sunny weather during winter mnths causes rapid transpiratin at a time when sil misture may be frzen. During summer, sunny, ht, and windy weather causes such rapid transpiratin that rts cannt physically keep up with the water lss. Sil water may be available, but rts may nt be functining prperly t absrb it. What causes rts t functin prly? Sil may be s cmpacted that rts cannt adequately explre sil fr nutrients and misture. Rts may be severed r therwise damaged frm cnstructin activities r garden cultivatin. Planting t deep limits xygen availability fr rts and stresses r kills them. A thick layer f mulch r black plastic cvering rt systems als injures them due t xygen deprivatin. Mechanical damage n lwer stems r trunks frm mwing equipment, imprper planting, imprper staking, animal chewing, r bring insects may als prevent r slw water uptake. The bttm line is that mre water is lst than can easily be replaced. Fr additinal infrmatin, refer the fllwing Clrad State University Extensin publicatins, available nline at Leaf Scrch, Extensin fact sheet #2,911 Tree Leaf Scrch, PlantTalk #2112 Figure 9. Leaf scrch n linden caused by hardscaping ver the rt zne. Oxygen Starvatin Oxygen starvatin ccurs when excess water in the sil drives ut xygen, in effect suffcating rts. Plants respnd by drpping lwer leaves that are usually yellwed r necrtic. Leaf lss is mst nticeable frm the inside f the plant ut

14 and the bttm up. In additin, leaves may be smaller than nrmal, grwth increments may be small, and the plant may have an verall unthrifty appearance. While xygen starvatin causes rt damage, the first clue that smething is wrng appears n the canpy, stems, and branches. These parts are the furthest frm the water surce, s the symptms appear there first. T cntrl prblems caused by water management issues, identify the likely causes and crrect them if pssible. This will require sme detective wrk t determine which factr r (usually) cmbinatin f factrs is causing the prblem. Management strategies are based n gd hrticultural practices. Fr example, add rganic matter t vegetable and flwer gardens befre planting t imprve drainage as well as water-hlding capacity. Cut back n irrigatin frequency r adjust the quantity f the water applied. Cre aerate turf, which will als benefit tree rts grwing in it. Apply and maintain mulch at levels apprpriate fr the material used. Remve any black plastic in the landscape. Weather Winter desiccatin is caused by dry winter winds that result in leaf water lss. Water cannt be replaced in the plant because the sil is t cld fr rt functin. Symptms f winter desiccatin include necrtic leaf r needle tissue (typically frm the tips inward), disclratin f needle r leaf tissue, and patchy damage distributin n individual plants in windy lcatins. Plants may nt exhibit symptms until the fllwing summer when drughty summer cnditins ensue (Figure 10). Figure 10. Winter dehydratin n pine appears n needle tips. T deter winter desiccatin, fall water plants after they g drmant. Rts are still active and can absrb water until sil temperatures drp belw 40 F. When the grund is nt frzen, additinal irrigatin may be helpful mnthly during the winter in the absence f snw cver r sufficient snwmelt r rainfall. Fr additinal infrmatin, refer the fllwing Clrad State University Extensin publicatins, available nline at

15 Envirnmental Disrders f Wdy Plants, Extensin fact sheet #2.932 Fall and Winter Watering, Extensin fact sheet #7.211 Fall and Winter Watering, PlantTalk #1706 Plant Grwth: Temperature, Clrad Master Gardener GardenNtes #143 Sunscald, PlantTalk #2111 Temperature Temperatures belw ptimal plant grwth cause plant damage. The amunt and type f damage depends n hw quickly temperatures drp, the lwest temperature reached, and hw lng cld temperatures are sustained. Freeze injury may be caused by frst crystals that frm in the freezing water utside f plant tissues r by freezing water inside plant cells. Damage frm the latter is much mre severe and resembles herbicide phyttxicity, bacterial blight, and branch flagging due t insect brer activity (Figure 11). Spring freezes damage exterir buds first, as these are the first t deharden. Fall freezes affect interir buds first as these are the last t harden. Damage f tissues is unifrm. Fr example, newly develping cnifer needles may be killed cmpletely r frm the tips inward. Figure 11. Sunscald r suthwest bark injury results frm rapid winter temperature changes. Temperatures abve ptimal grwth cause plant damage as well. The mst severe injury ccurs n leaves that are expsed t the sun and tissue that is furthest away frm water such as uter branch tips, leaf margins, and between leaf veins. Fr additinal infrmatin, refer t Clrad Master Gardeners GardenNtes #143, Plant Grwth: Temperature, available nline at Chemical Injury Chemical injury is plant damage caused by pesticides, fertilizers, de-icing salts, and ther prducts. Example 1. The client says, Why has my spruce tree turned a different clr after the Certified Arbrist sprayed hrticultural il t cntrl the Duglas Fir tussck mth?

16 Herbicides Herbicides (weed killers) damage plant tissues by causing symptms such as chlrsis, necrsis, distrtin, and elngated grwth. Glyphsate, dicamba, and 2,4-D are examples f cmmn herbicides that cause chemical injury t desirable plants when used incrrectly. Herbicides that behave like plant grwth regulatrs, such as dicamba and 2,4- D,translcate thrugh bth the xylem and phlem. They stimulate grwth such as cell divisin, elngatin, and fruit and flwer prductin (Figure 12). Figure 12. Damage n grapes frm 2,4-D. Ntice the distrtin in leaf vein pattern. Excessive cncentratins f these chemicals cause twisting and curling f stems, stem swelling, weakened cell walls, rapid cell grwth, and cellular and vascular damage and death. Grasses are nt affected by plant grwth regulatrs apparently due t a different arrangement f vascular bundles (xylem and phlem). Glyphsate is an amin acid inhibitr that interferes with synthesis f certain amin acids needed t build prteins. Glyphsate mves thrugh the phlem t the new grwth f shts and rts. Injury symptms include chlrsis, shrtened interndes (cmpact grwth r stunting), stem prliferatin, and mimics damage caused by 2,4-D and ther plant grwth regulatrs, viruses, phytplasmas, eriphyid mites, and envirnmental factrs. Fertilizers An excess r shrtage f the 17 essential elements required fr plant grwth and develpment may cause plant damage. Excess amunts f fertilizers can burn plants due t the level f salts in fertilizers. Symptms f fertilizer damage include leaf margin necrsis (similar t drught stress in appearance), leaf disclratin, sft rapid grwth, and vegetative grwth at the expense f flwer and fruit prductin. Nutrient deficiencies include chlrsis, interveinal chlrsis, blssm-end rt, stunting, and purpling. Symptms f nutrient excesses and deficiencies may be cnfused with disease, insect, mite, r ther envirnmental prblems. If a sil nutritinal prblem r salt injury is suspected, have the sil tested. When excess fertilizer has been applied, apply water in an effrt t leach salts frm the rt zne. Quick release fertilizers are mre prne t burn plants. Fllw label directins when applying fertilizers t avid plant damage

17 Salts It is cmmn practice in Clrad t use de-icing salts t remve snw and ice frm radways and sidewalks. Salts injure plants frm 1) salt burn n fliage, 2) rt burn f salts, r 3) sil buildup that deterirates sil structure, interfering with drainage and rt grwth. Symptms f salt spray n leaves include stem and leaf defrmities, witches brms, and twig dieback f deciduus plants. Cnifers exhibit needle brwning at the tips f branches. Salt spray damage is nly nticeable n the plant side adjacent t a rad. Symptms f salt accumulatin in sils are different frm salt spray and include marginal leaf scrch, stunting, and twig dieback. Leaf scrch may nt appear until later in the seasn r in fllwing seasns. T reduce salt burn, avid de-icing salts, add rganic matter and charcal t the sil, leach with water, r prtect plants using a barrier that will keep salt-laden snw away frm plant material. Fr additinal infrmatin, refer t Clrad State University Extensin fact sheet #7.425, Magnesium Chlride Txicity in Trees, available nline at Cmpst and ther sil amendments can be high in salt when made with manure r bislids. Symptms f salt burn include marginal burning f leaves, stunting, rt dieback, and death f plants. Fr additinal infrmatin, refer t Clrad Master Gardener GardenNtes #241, Sil Amendments (Figure 13). Figure 13. Salt damage n bean leaf burns the margin f the leaf. This was caused by using cmpst high in salts. Plant Disease Diagnsis Generic steps in the diagnstic prcess include the fllwing: 1. Identify the plant. 2. Identify the prblem(s). a. LOOK Define the prblem by describing the signs and symptms. 1) Identify nrmal characteristics f the plant 2) A systematic evaluatin f the plant helps rganize questins in a methdical prcess. b. READ Distinguish between pssible causes by cmparing signs and symptms with details in reference materials. c. COMPARE Determine prbable cause(s) thrugh cmparisn and eliminatin. 3. Evaluate if management effrts are warranted

18 a. What type f damage/stress des this disrder/pest cause? b. Under what situatins wuld management effrts be warranted? c. Are management effrts warranted fr this situatin? 4. Evaluate management ptins effective fr this disrder/pest and when they are applied. Determining the causal agent f plant damage can be a tumultuus endeavr, s let us expand n cntent arund Step 2, Identify the prblem(s). Use a systematic apprach when diagnsing plant damage and determinatin will becme easier (see Chart 1). The prbability f crrectly diagnsing plant damage based n ne r tw symptms is lw. In cntrast, prbability f crrectly diagnsing plant damage based n many symptms and factrs is high. Therefre, using investigative skills and asking many questins is imperative t arriving at a crrect diagnsis. [Chart 1] Fr additinal infrmatin n the diagnstic prcess, refer t Clrad Master Gardener GardenNtes #102, Diagnsing Tree Disrders, available nline at Chart 1. A flw chart displaying the systematic apprach t determining causal agents f plant damage. Start here 1. Identify plant 2. Identify the prblem (lk, read, and cmpare) Identify nrmal characteristics Evaluate surrundings Identify pattern f damage Unifrm = abitic agent Randm = bitic Prblem identified OR Distinguish amng abitic agents Distinguish amng bitic agents Sample Questins Accurate diagnsis is abslutely dependent n accurate bservatin. When making bservatins we must ask the fllwing questins: 1. What symptms is the plant expressing? 2. Hw many plants are affected? 3. Is there a pattern assciated with the prblem (i.e. is the prblem lcated in ne area; such as a lw area, n the nrth side, suth side, etc.)?

19 4. Are there any differences in susceptibility f varieties r species (i.e. is it just the tmates r are ther plants als affected)? 5. Ask abut bvius causes first, such as animals, frst, flding, r mechanical damage. 6. Determine which part f the plant is actually damaged. Wilts, fr instance, frequently are nly a respnse t sme damage t the rts. Dieback f branches is smetimes caused by cankers r mechanical damage further dwn the stem. 7. Are the rts healthy appearing (nt black r mushy) and mist? Nte: Yu may nt be able t diagnse the prblem withut rts. 8. What abut the texture and wetness f the sil? Is it t heavy, sandy, r cmpacted? Is salt crusting evident? 9. What is the weed ppulatin? (Weeds may indicate a particular sil prblem.) 10. Find ut as much as pssible abut the previus histry: fertilizer, pesticides, land leveling, cultivatin methds, irrigatin schedules, and climatic cnditins. 11. There are many ther questins that yu may think t ask based n the specific sample in questin. Remember, we can never ask enugh questins. The mre thrugh yu are, the better the diagnsis. Determine what the nrmal plant wuld lk like during that time f year. Describe the damage using terms like gall, witches brm, and chlrtic. Establish the lcatin n the plant where initial damage ccurred. Fr example, there are leaf spts with fruiting structures n the underside f leaves, but these symptms are nt what caused tree death. Cankers alng the branches and trunk are what killed the tree. Distinguishing the factr that caused plant death frm ther symptms and signs can be tricky. In turfgrass, many times sclertia, fruiting bdies, and cnidia are sptted in necrtic and prblematic areas. Hwever, these disease-causing structures may nt be related t turfgrass death. Identify Pattern f Plant Damage Unifrm damage patterns n individual plants and n many different plants in a specific area are typically characteristic f nnliving r abitic factrs. Abitic factrs include mechanical, physical, r chemical factrs. Randm damage patterns n individual plants r n a specific family r genus f plants typically indicates a living r bitic agent f disease. Bitic factrs include fungi, bacteria, r nematdes. Imprtant nte: Yu may cme t a diagnsis based n the answers a client prvided, but when duble-checking the diagnsis, yu may realize the diagnsis des nt seem quite right. Keep an pen mind, g back thrugh yur questins, and take a different diagnstic avenue. Distinguish Between Bitic and Abitic Factrs Signs f bitic pathgen activity will always be present. It is a matter f whether the sign is bserved. First, clsely study plant damage. Mentally identify pssible

20 causal agents. Then lk fr signs that wuld accmpany such damage. Signs f disease include fruiting structures, verwintering structures, mycelium, insect frass r carcasses, and ze. Because sme diseases are vectred by insects, signs that the vectrs are present are equally as imprtant as finding signs f the disease. In additin, sme types f disease symptms mimic symptms f insect r vertebrate damage. It is critical, therefre, t distinguish between insect and pathgen damage using bserved r unbserved signs f bth insects and pathgens. If n signs are bserved, abitic activity shuld be cnsidered. Ask questins regarding mechanical, physical, and chemical factrs affecting the damaged plant. Mechanical factrs include string trimmer damage t tree trunks, imprper pruning cuts, injury during transprtatin f plant material and guy wire damage. Physical factrs include temperature extremes, light differentials, and extreme changes in xygen and misture levels. Chemical factrs include pesticide damage, fertilizer damage, nutritinal disrders, and pllutants. Authr: Mary Small, Clrad State University Extensin. Artwrk by David Whiting; used by permissin. Figures 2,3, 6 and 10 by Mary Small and Figure 10 by Curtis Utley, bth f Clrad State University Extensin. Clrad Master Gardener GardenNtes are available nline at 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. Revised Nvember