Disease Control for Trees, Shrubs and Flowers Alan Windham, Professor Entomology and Plant Pathology 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