Published on February 18, 2014
2/18/2014 DISEASE IDENTIFICATION OF HERBACEOUS LANDSCAPE PLANTS Amy Timmerman Extension Educator What are plant diseases? Anything that prevents a plant from performing to its maximum potential. University of Nebraska-Lincoln Extension Institute of Agriculture and Natural Resources Types of disease Abiotic Disease caused by a non-living agent Sun scorch, nutrient deficiencies Biotic Disease caused by a living agent. Fungi, bacteria, nematodes (pathogens) Viruses Too small to be seen with light microscope Transmitted by aphids, mites, other insects, nematodes, and fungi Virus acquired by insects through feeding on infected plant tissue What size are plant pathogens? Nematode head Plant cell viruses fungus bacterium Common plant pathogens and their size relative to each other and to a plant cell Plant cell nucleus Bacteria Single-celled organisms An opening is required for infection to occur. Favored by humid conditions. Can survive in soil and in/on plant debris. 1
2/18/2014 Nematodes Fungi Hyphae – small thread-like filaments Mycelium – mass of hyphae Spores – reproductive structures Most fungi require free moisture to cause infection of plants Can survive in soil or on plant debris Microscopic worm-like animals Feed on roots and above ground plant parts. Roots become distorted or galled after feeding occurs. Some are vectored by insects. Can survive in soil, in plants, and in insect vectors. Disease PathoSystem Components environment Disease Development Light or No Disease Pathogen Environment Host host pathogen Disease Development amount of disease = overlap of system components Disease Development With ornamental plant diseases management can be a significant factor in influencing disease development because it impacts all three factors; the host, the pathogen and the environment. impact on the host = timing of overlap 2
2/18/2014 Symptom Distribution Symptom Distribution – Field Field-Plant-Leaf Scale Field Distribution Patterns Site operations Obstacle Planting dates and methods Soil Modification prior to planting Disease History in the area Chemical(s) applied the current and previous years Field Distribution Patterns: Landscape Position Adjacent landscape or position within the landscape. Position Field Distribution Patterns: Landscape Position Adjacent landscape or position within the landscape. Position Proximity Entrance Field Distribution Patterns: Irregular Pattern Many of these are clumped as an overall distribution pattern. Proximity Summer Patch 3
2/18/2014 Field Distribution Patterns: Irregular Pattern Topography associated distributions. Low Elevations Soil Factors High Elevations * Not pictured is slope associated factors. Symptoms Distribution Patterns Is this abiotic or biotic? Field Distribution Patterns: Uniform Evenly distributed with maximal distance between neighboring affected areas. Field Distribution Patterns: Uniform Equipment/Application Operations 4
2/18/2014 Symptom Distribution Patterns Photo Courtesy of William M. Brown Jr. – Bugwood.org Symptoms Distribution Patterns Symptom Distribution By combining the distribution on the plant with the field distribution you may start to build clues as to the cause of the observed symptoms. Know the Plant Healthy plant appearance Variety / cultivar Is this plant sick? Time of symptom development Plant part(s) affected (roots, leaves, stems, etc.) – remember foliar symptoms are often due to root problem 5
2/18/2014 Symptom Distribution – Plant Symptom Distribution – Plant Know the Growing Conditions Symptom Distribution – Plant Precipitation Distribution Map Soil type and pH/soil modification Soil drainage and compaction Moisture availability Current and previous weather conditions Occurrence of unusual environmental conditions (i. e. extreme temperature changes) < 16” 20” 24” 30” > 34” Oregon Climate Service OSU 1961-1990 annual precipitation 6
2/18/2014 Symptom Distribution Symptom Distribution – Leaf Identifying the distribution of plant symptoms on individual plant parts will also help with your diagnosis. Symptom Distribution – Leaf Perennial Problems •Right plant, right place •Site selection •Watering •Full sun, shade •Soil conditions •Exposure Herbaceous Plants Black Spot of Rose Fungus Common foliar disease Leaf wetness and warm temperatures favor disease Leaf spots begin on bottom leaves of plants and spread upward Fungus survives in leaf debris 7
2/18/2014 Black Spot of Rose Resistant cultivars Fungicide applications throughout growing season Rose Rust Resistant cultivars Plant may defoliate early Fungicide applications Rose Mosaic Virus •Virus •Yellowing along veins or mosaic patterns in leaves •Systemic in plant •May cause stunting •Often transmitted during grafting of roses, not vectored by insects Rose Rust Fungus Orange pustules of fungus on leaves and buds Orange color will rub easily onto fingers Spores of fungus are airborne Rose Rosette Virus Vectored by mites Systemic in plants Stunted, bushy stems with reddish coloration and excessive thorns Diseased plants should be removed Powdery Mildew Fungus White powdery growth on leaf surface High humidity in leaf canopy favors disease development 8
2/18/2014 Powdery mildew on delphinium Powdery mildew on gerbera Powdery Mildew Resistant cultivars Plant may defoliate early Fungicide applications usually not necessary Botrytis Blight Fungus Can affect leaves and blossoms Moisture favors disease Sanitation helps https://www-s.aces.uiuc.edu/photolib/lib17//midsize/botrytis%20on%20rose%20flowers.jpg to control disease http://www.viette.com/images/tips/BotrytisPeony69.jpg Botrytis on lisianthus Botrytis on rose 9
2/18/2014 Aster Yellows Mycoplasma Vectored by leafhoppers Many hosts including strawflower, purple coneflower, marigold, aster, etc. Stunting of plants and flower petals often resemble leaves Diseased plants should be removed Leaf Spot of Iris • Fungal • Small brown spots with water soaked margins • Spots enlarge and develop reddish-brown boarders • Leaves can die • Management • Remove infected leaves • Avoid overhead irrigation Phytophthora blight •Fungus •Peony and rhododendron •Wilting branches and necrotic leaves •Fungus survives in the soil and infects through the roots Cercospora Leaf Spot of Hydrangea • Fungal • Tan spot with reddishbrown halos • Develops on lower foliage first • Seen in low-maintenance landscapes • Late summer to early fall • Management • Avoid overhead irrigation • Apply nitrogen • Fungicide applications with mancozeb, copper or chlorothalonil Crown Rot of Iris •Fungal •Leaves die slowly from the tips •White fungal threads are visible at leaf base •Tan sclerotia develop between rotting leaves •Management •Discard infected bulbs Fusarium Wilt of Gladiolus •Fungus •Vascular disease causes browning and wilting of leaves •Discoloration of bulb is evident •Fungus survives in the soil 10
2/18/2014 Phytophthora Stem Rot of Vinca Management of Vinca Stem Rot •Wilting and dieback of stems •Dark brown to black lesions on the stems and branches •Occurs in extremely wet soils • Water Management Stem Blight of Vinca •Dark brown to black girdling lesions at ground line •Yellowing and dieback of runners •Can also cause leaves to turn brown and wither •Observed during cool wet weather typically in the spring Black Knot Fungus Causes galls on twigs and branches Black color comes from fungus Branches die from galling, may take several years Prune affected branches Fungus overwinters in galls • Avoid overhead watering when possible • Reduce watering, only when needed • Improve drainage • Sanitation • Removing plants showing symptoms • Pruning out affected areas can also help Management of Stem Blight •New beds •Plant only vigorous, disease-free plants •Water only enough to maintain vigor •Annual spring fungicide drenches are available for beds with serious problems Crown Gall Bacteria Many different hosts Causes galls on twigs Smaller twigs may be girdled Numerous galls may cause stunted plants with discolored leaves Bacteria enter plants through leaves 11
2/18/2014 Bacterial Wilt of Geranium Bacteria Typical v-shaped lesions with yellow margin Wilting of entire plants Bacteria can be moved by handling and watering Bacterial Leaf Spot of English Ivy •Circular, dark brown to black spots •Yellow halos surrounding lesion •Leaves turn yellow and die •Management •Discard infected plants •Avoid overhead irrigation Impatient Necrotic Ringspot virus • Symptoms vary with plant species • Infects several plant species including: • Aster *Marigold • Mum *Phlox • Coleus *Petunia • Columbine • Snapdragon • 44+ ornamentals • 11 vegetables • 12 Weeds Septoria Leaf Spot of Gillardia •Tan spots containing tiny dark brown to black dot-like structures •Management •Avoid overhead irrigation Hosta Virus X •Symptoms vary including •Stunting •Puckering •Mottling, chlorosis, “ink-bleed” •Leaf twisting •Necrosis •Death •Transmitted by propgation Foliar Nematodes •Lives briefly in the soil but prefers above ground plant parts •Infects several plant species • Transmitted by western flower thrips 12
2/18/2014 Foliar Nematodes - Symptoms • Yellow, brown to purple to black wetlooking areas • Angular, yellow areas on the leaf bounded by the leaf veins • General yellowing, reddening or bronzing of leaves • Death of leaves • Cupping and distortion of leaves • Chlorosis Edema Foliar Nematodes - Management •Discard infected plants •Avoid overhead watering •Space plants so they can dry quickly Nutrient Deficiencies • Abiotic • Cool, cloudy, wet weather • Water-soaked pimples or blisters underside of leaf • Blisters become corky brown • Severely infected leaves fall What’s Wrong? 13
2/18/2014 What’s Wrong? The accuracy of the diagnosis is often a function of the quality of the sample collected and the thoroughness of the background information provided. Department of Plant Pathology University of Nebraska-Lincoln Institute of Agriculture and Natural Resources 14
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Selected Reference Materials for Plant Disease Diagnosis ... Abiotic Disorders of Landscape Plants: ... Pests and Diseases of Herbaceous Perennials: ...
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ID-88 Woody Plant Disease Management ... on high value landscape plants. Disinfest tools between cuts. Ap-ply Gallex to exposed galls. Do not
Minnesota Specific References . ... reference of common insect pests and diseases of woody landscape plants. ... Pests & Diseases of Herbaceous ...
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