Disease Control for Trees, Shrubs and Flowers

Home , Bordeaux mixture, Fire blight, Lophodermium

Alan Windham, Professor

Disease Hosts Management Strategies* Powdery mildew is easily identified by Amelanchier, azalea, Host Resistance – use disease resistant the presence of white to gray mycelium begonia, columbine, species/cultivars for crabapple, crape on affected leaves and/or flowers. The crabapple, crape myrtle, myrtle, dogwood, lilac, rose, zinnia first sign of disease is usually isolated dogwood, euonymus, Chemical Control- azoxystrobin, colonies of white fungal growth. With hydrangea, lilac, chlorothalonil, copper hydroxide, copper time whole leaves may be totally covered magnolia, nandina, oak, octanoate, kresoxim-methyl, myclobutanil, with fungal growth. On some plants, phlox, rhododendron, polyoxin D, propiconazole, pyraclostrobin, such as pin oak, mildew may be present rose, sedum, tulip tree, tebuconazole, triadimefon, only on the undersides of leaves. On verbena, zinnia trifloxystrobin, triflumizole dogwood, crape myrtle and nandina infected leaves may be curled, twisted or otherwise distorted. Leaves may be abnormally red with little mycelium visible; on sedum lesions are scabby and brown. Downy mildew -Although this sounds Alyssum, brambles, Host Resistance- for downy mildew of similar to powdery mildew, the diseases coleus, grape, impatiens, garden impatiens use begonias, coleus, are very different; caused by fungi from pansy, rose, rudbeckia, New Guinea impatiens or SunPatiens. entirely different taxonomic classes. The salvia, snapdragon, Chemical Control – azoxystrobin, fungi that cause downy mildew are more tobacco, viburnum cyazofamid, dimethomorph, fenamidone, closely related to fungi that cause fluopicolide, fosetyl-al, mancozeb, phytophthora and pythium root rots, mefenoxam, potassium salt of phosphorus than the fungi that cause powdery acid, potassium phosphite mildew. Symptoms of downy mildew can range from leaf spots and defoliation to rapid blighting of diseased shoots. Angular leaf spots on rose may range from red to brown to black. Signs to look for include gray-to-white tufts of mycelium on the undersides of leaves, directly below chlorotic lesions. Look for mycelium early in the morning while the leaves are still wet. Gray mold may be found on herbaceous Almost any herbaceous Sanitation – in greenhouses and and woody ornamentals usually during or woody plant propagation areas, remove infected plant cloudy, cool, moist weather. Stems, parts or plants leaves and flowers may be attacked. Environmental – in greenhouses use fans Woody ornamentals in overwintering and vent to remove moist air at the end of structures may become infected. the day. Minimize leaf wetness. Symptoms of infection are blighting of flowers, tan to brown leaf spots, shoot blights and stem rot. A sign of disease is gray-brown mold on diseased plant parts. Disease Hosts Management Strategies* Chemical Control – chlorothalonil, copper sulphate pentahydrate, fenhexamid, fludioxonil, iprodione, mancozeb, triflumizole Rusts -Signs include bright yellow, Amelanchier, apple, Host Resistance – cedar rust resistant orange, reddish-brown or chocolate- aster, azalea, cedar, cultivars are available for apple, crabapple, brown raised pustules are visible usually crabapple, daylily, hawthorn. on the undersides of leaves. Gelatinous fuchsia, geranium, Chemical Control – azoxystrobin, tendrils of rust spores are produced from grasses, hawthorn, chlorothalonil, mancozeb, myclobutanil, galls each spring on eastern red cedar hemlock, hollyhock, iris, propiconazole, pyraclostrobin, infected with cedar-apple rust. Pine jack-in-the-pulpit, tebuconazole, triadimefon, trifloxystrobin needle rust produces pustules on pine juniper, mayapple, oak, during spring. Early symptoms on leaves pear, pine, potentilla, are yellow leaf spots. Rust galls may quince, snapdragon, appear on stems of pine, cedar and sunflower hawthorn. Twig rust may cause branch dieback on plants as diverse as hawthorn and hemlock. Daylily rust was first found in the U.S. in 2000 and in TN in 2001. Virus Diseases -Plants infected with Canna yellow mottle Sanitation and Cultural Control – Do not viruses exhibit a variety of symptoms virus – Tropicana series propagate plants with symptoms of a viral including: mosaic, ringspots, stem of canna lily disease. In production, remove and lesions, rosette (witches broom), “oak- Hosta Virus X- many discard infected plants. For impatiens leaf” pattern, stem pitting, stunting, common cultivars of necrotic spot, monitor and manage thrips flower break, etc. Hosta virus X (HVX) is hosta populations in greenhouses. fairly common on hosta. HVX is most Impatiens necrotic spot Rose rosette – remove roses with easily diagnosed on gold hosta cultivars virus- over 350 symptoms of rose rosette. Break up mass where abnormal green stripes appear ornamental plants plantings by using a non-host as a barrier parallel with veination of leaves. Canna Tomato ringspot virus- between smaller plantings. Remove yellow mottle virus is very prevalent on dogwood, fringetree, multiflora rose near rose plantings. the Tropicana series of canna. Symptoms peach, cherry Pruning and control of the vector include stunted plants, necrotic streaks in Tomato spotted wilt (eriophyid mites) are being evaluated. leaves and muted variegation. Rose virus – perennial plants rosette is a viral disease transmitted by Rose mosaic virus and eriophyid mites. Virus diseases may be Rose rosette- rose difficult to diagnose unless you are familiar with symptoms associated with specific virus diseases. Leaf spot diseases are usually caused by Alternaria LS -aucuba, Host Resistance- choose disease resistant fungi, but a few may be caused by impatien, marigold, cultivars of rose, crabapple, Indian bacteria. These are among the most zinnia hawthorn, buckeye, horse chestnut common plant diseases. Symptoms vary Black spot - rose Sanitation and Cultural Control– rake and depending on the pathogen and host. Bull’s eye LS - magnolia, remove diseased leaves. Minimize leaf Some common symptoms include: maple wetness; use drip irrigation. frogeye or bull’s eye spot marked with Cercospora LS - buckeye, Chemical Control – azoxystrobin, concentric rings; irregular, round tan crape myrtle, leucothoe, chlorothalonil, copper hydroxide, copper spots with small black fruiting bodies; laurel, red bud, rose octanoate, kresoxim methyl, mancozeb, angular tan or black spots; black or tan Entomosporium LS – myclobutanil, propiconazole, spots surrounded by a yellow “halo”; oval Indian hawthorn, pear, pyraclostrobin, tebuconazole, thiophanate shaped leaf spots; and tan to gray spots photinia methyl, trifloxystrobin, triflumizole with red or purple margins. Fungal leaf Leaf blotch – buckeye, Disease Hosts Management Strategies* spot diseases are usually favored by wet horse chestnut seasons, high humidity and/or frequent Phyllosticta LS - holly, overhead irrigation. Many leaf spots magnolia, maple, witch cause premature defoliation. hazel Scab - crabapple Shot Hole Diseases - Some plants shed Almond, apricot, cherry, Sanitation and Cultural Control– Rake and diseased leaf tissue in response to fungal cherry-laurel, peach, remove fallen leaves. Minimize leaf or bacterial infections. Infected leaves plum (plants in the wetness, especially for bacterial shot hole are covered with circular, “shot” holes genus Prunus) diseases of laurel. where diseased tissue has fallen out. Chemical Control –chlorothalonil, copper Infected leaves may become chlorotic hydroxide, copper octanoate, mancozeb and drop prematurely. Shot-hole diseases may be caused by fungi or bacteria. Damage from shot-hole disease may be confused with insect feeding. Remember, shot-hole disease only occurs on plants in the genus Prunus. Similar symptoms on other plants may be caused by insects. Anthracnose refers to diseases that Ash, dogwood, Sanitation and Cultural Control– Rake and cause leaf, stem and/or fruit lesions. euonymus, hosta, remove fallen leaves. Prune and remove These diseases may appear as irregular maple, oak, sycamore cankered or dead branches. Space to leaf spots/lesions along leaf margins and increase air movement and minimize leaf across or between veins. Anthracnose wetness. Use drip irrigation to minimize may kill entire leaves, young shoots and leaf wetness. twigs, plus cause premature defoliation. Chemical Control –chlorothalonil, cupper Diseased leaf tissue may fall out of leaf hydroxide, copper octanoate, lesions. Stem cankers may form at the tebuconazole, thiophanate methyl base of succulent shoots. Look for anthracnose diseases of ash, dogwood, maple and sycamore during April and May. Needle Blight and Cast of Conifers - Cyclaneusma needle Sanitation and Cultural Control – For field Basically a leaf spot disease of conifers cast - scots pine grown plants, choose locations with good that leads to premature shedding of Lophodermium needle air movement. Space plants to minimize needles. During certain times of the cast - Eastern white pine needle wetness. For needle blights such year, distinct yellow to brown lesions are Ploioderma needle cast as Kabatina, prune if desired to remove visible on pine needles. Infected needles - loblolly pine diseased shoots. turn brown and shed. Fungi that cause Rhizosphaera needle Chemical Control – chlorothalonil, copper needle cast are generally weak pathogens cast, Stigmina needle hydroxide, thiophanate methyl that infect older needles in the interior of cast - spruce the tree’s canopy. Black fruiting bodies Phomopsis blight - of various fungi may be observed in juniper single or multiple rows along the length Kabatina blight - of infected needles. Conifers infected juniper, Leyland cypress with needle cast have brown needles and Passalora needle blight thin canopies. – Leyland cypress The most common tip blight diseases of juniper include phomopsis blight which attacks new flushes of growth in late spring or early summer. Kabatina blight Disease Hosts Management Strategies* of juniper attacks juniper injured from snow or ice in late winter through early spring. Tip blights rarely kill more than four inches of the terminal of juniper shoots. Canker Diseases - Canker causing fungi Botryosphaeria canker - Sanitation and Cultural Control – for may live as endophytes on susceptible ash, crabapple, fungal canker diseases, keep plants host. An endophyte means the fungus is dogwood, juniper, irrigated during dry periods, remove living on and/or in host tissue, but there laurel, Leyland cypress, diseased branches, remove heavily are no signs of disease. But let the plant red bud, maple, cankered plants. come under significant stress and dieback rhododendron Fire blight – streptomycin may be used may not be far away. Endothia canker - pin during bloom, copper sprays afterward. Leaf death and twig dieback are some of oak Dormant pruning to remove cankered the first symptoms of canker diseases. Fire blight - apple, branches. There are apple, crabapple and Cankers are usually found on branches cotoneaster, crabapple, pear cultivars resistant to fire blight. but may infect trunks of young trees. The hawthorn, pear, disease may be initially undetectable pyracantha, serviceberry except by shaving the surface of a branch Nectria canker - to reveal brown discoloration of bark dogwood, pear and/or underlying sapwood. As cankers Phomopsis canker - enlarge, oval, sunken areas may develop azalea, ash on branches. Large cankers may girdle Seiridium canker - and kill branches and entire plants if they Leyland cypress, Arizona develop on the trunk or main stems of cypress shrubs. Gum production (gummosis) is Thyronectria canker - often associated with fungal and honey locust bacterial cankers of cherry. Resin is often associated with canker diseases of junipers. Fire blight is a bacterial disease that may cause cankers. Fire blight is usually observed on plants in the Rosaceae family. Early symptoms may be blossom blight during bloom, followed by the shoot blight phase and signature symptoms such as shoots killed rapidly in the shape of a ‘shepherd’s crook’. Water soaked cankers may be found on the trunk and branches of infected plants. Leaf galls - Conspicuous white, yellow, Leaf gall - Azalea, Azalea leaf gall can be removed and red or gray blisters or galls develop on blueberry, camellia,, destroyed. leaves. Leaves may become puffy, rhododendron Peach leaf curl – two to three fungicide puckered, thickened or curled. Infected Leaf blister - red oak, sprays. At 50% leaf fall in late October, leaves may drop early. The most water oak, willow oak one to two dormant sprays in late winter common leaf gall diseases are azalea leaf Leaf curl- peach, plum before flower buds open. Chlorothalonil, gall, peach leaf curl and oak leaf blister. Bordeaux mixture, lime sulfur, fixed Symptoms may be confused with insect copper. or mite induced galls which are more numerous. Crown gall - Rough-surfaced, hard or Apple, crabapple, Sanitation and cultural – crown gall may soft, spongy, swollen tumors or galls up Euonymus, holly, maple, be more severe in heavy soils where water to several inches in diameter may form peach, plum, stands. Avoid fields with a history of crown Disease Hosts Management Strategies* on stems or roots. Galls may be flesh rhododendron, rose, gall. Destroy infected ornamental plants colored, greenish or dark. Galls are willow, wisteria with crown gall. usually found near or below the soil-line. Galls may form at wounds made during propagation. As galls continue to develop and enlarge, surface layers may become brown, woody and roughened. Plants with crown gall usually become unthrifty and possibly stunted. Plant death may eventually occur. Stem Rots Southern Blight- Ajuga, Sanitation and Cultural Control – for Southern blight - Usually occurs in apple, clematis, southern blight and Sclerotinia crown rot, gardens, perennial borders and nurseries crabapple, forsythia, remove infested plants plus soil near the during hot weather, near mid-summer. hosta, many annual and stem as to remove sclerotia. Symptoms include wilting, leaf scorch perennial flowers, rarely Chemical Control – followed by plant death. Signs of disease on some turf species Southern blight and Rhizoctonia stem include white mycelium on the stem of Sclerotinia Stem Rot - rot– azoxystrobin or flutolanil as directed infected plants and tan to reddish-brown Campanula, euonymus, spray or drench for prevention of stem round, spherical resting structures of the several herbaceous rots fungus (sclerotia) on the stem and soil flowers Sclerotinia crown rot – thiophanate surface. Rhizoctonia stem rot - methyl Sclerotinia crown rot - Unlike southern many herbaceous plants blight, this disease usually appears during and seedlings of woody mid-spring to early summer when plants and conifers conditions are cool and moist. Affected plants usually wilt and die. White mycelium may be visible on stems near the soil surface. Black, oblong sclerotia may be present on the outer surface of woody plants or in the stem pith of herbaceous plants. Diseased stems should be split lengthwise and examined for signs of sclerotia. Rhizoctonia stem rot/damping off - This disease is often the cause of damping off (stem rot) of seedling plants. Seedling annual or perennial flowers or woody ornamentals may be killed by this fungus after it attacks the stem near the soil surface. Diseased seedlings often fall over and die. In the field, the fungus may move short distances down the row killing several adjacent plants. In propagation beds or flats, diseased plants may be killed in circular areas as the fungus moves outward. Nematode Diseases - Millions of Root knot nematode - Sanitation and Cultural Control - avoid nematodes may live in a square meter of Abelia, aucuba, begonia, planting susceptible hosts into infested soil, however, only a few are parasites of boxwood, dogwood, soil. Destroy infested plants. Do not plants. Most plant parasitic nematodes gardenia, holly, propagate plants infested with foliar attack plant roots; some attack foliage. hydrangea, impatien, nematodes or root knot nematode. Disease Hosts Management Strategies* Nematode damage can be difficult to ligustrum, nandina, diagnose as most of the damage occurs photinia, rose below ground. Plants damaged by Foliar nematode - nematodes may appear stunted, African violet, anemone, unthrifty, discolored and have discolored begonia, brunnera, roots with lesions or galls. One sure way hosta, many shade to identify nematode problems is to loving perennials submit a soil and/or root sample for Lesion nematode - analysis at a plant diagnostic laboratory; boxwood, juniper submit symptomatic foliage where foliar nematode is suspected. Wilt diseases are usually responsible for Bacterial leaf scorch - Sanitation and Cultural Controls – Plant the slow to moderate decline of trees elm, red maple, diversity prevents the loss of large and some shrubs. Individual branches mulberry, sycamore, pin numbers of street trees. Plant diverse tree may discolor and die. Some wilts may oak, shingle oak species. affect only one side of the plant. A Dutch elm disease - elm Dutch elm disease –remove and destroy common symptom associated with wilt Verticillium wilt - ash, infected trees to limit spread of elm bark diseases is vascular discoloration barberry, boxwood, beetles. Trees of high value may be (discolored sapwood). Leaf scorch and a buckeye, catalpa, injected with fungicides by arborists. reduction in canopy size are additional daphne, elm, lilac, Verticillium wilt – do not plant susceptible symptoms. Wilt pathogens may be euonymus, smoke tree, maple into infested fields. Replace spread by insects (Dutch elm disease by maple diseased shade trees with resistant elm bark beetles; Bacterial leaf scorch by Fusarium wilt - mum, species. leaf hoppers). Bacterial leaf scorch is very more common on common on pin oak, other oaks in the herbaceous plants red oak family. Root Rot - Plants affected with fungal Black root rot - Japanese Sanitation and Cultural Controls- check root rots may be stunted, wilted, look holly, blue holly, root health, if possible, prior to purchasing generally unthrifty (mimic nutrient inkberry, vinca, pansy, plants in containers. deficiency) and eventually die. petunia Phytophthora root rot – avoid planting Discolored decayed roots are sure Phytophthora root rot - susceptible plants into heavy, poorly symptoms of root rot diseases. Poor azalea, dogwood, drained soils. Avoid soil contamination of drainage, standing water, improperly forsythia, fir, holly, new pots and bark media. Place container constructed landscape beds, planting juniper pieris, plants on gravel or ground cloth. Irrigate infected plants and excessive irrigation rhododendron, yew from water sources free of Phytophthora. favor phytophthora and/or pythium root Black Root Rot – alkaline soil pH favors rots. disease development. Avoid soil contamination of flats, pots and soil-less media. Chemical Control – Phytophthora root rot- cyazofamid, etridiazole, fluopicolide, fosetyl-Al, mefenoxam, mono and di-potassium salts of phosphorous acid, potassium phosphite Updated Feb 2014

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