Diagnosing Plant Diseases Plant Pathology Diagnosing Problems Ask questions! Listen! Ask more questions! Lisa Sanderson Extension Agent, ANR Henrico County What You Need to Know What is a Plant Disease? Biotic and abiotic causes of plant diseases Organism responsible for problem Conditions Diagnosing plant damage Signs and Symptoms Control Resource Materials May be any disturbance that prevents the normal development and reduces its economic or aesthetic value Problems Problem Causing Organisms Biotic are caused by Living Factors Abiotic are caused by Non-living factors Biotic Fungi Bacteria Virus Nematodes 1
Fungi Bacteria Filamentous (threadlike) organism Can grow inside or outside plant tissues Reproduce, spread, persist via spores Common Symptoms Leaf spots and blights Fruit, stem, root wood and seedling rots Cankers Vascular wilts Galls Mildew and rust diseases Minute, one celled organism Large masses visible as ooze or slime Need a microscope to see Can behave similarly to viruses Common Symptoms Leaf spots and blights Stem and fruit rot Cankers Galls Vascular wilt Viruses Infectious modules (clumps) Take over a plants metabolism to reproduce Symptoms Poor growth Mottling or mosaic Leaf crinkling Nematodes Microscopic, none-segmented round worms Treated separate from insects and mites (accident of history) Many live in soil and feed on roots, while some live inside leaves and shoots Symptoms Poor root development Root galls Swollen root tips Abnormal root branching Yellowing of foliage Conditions Disease Cycle Too wet Too dry Humidity Temperature Pathogen Host Other 2
The Disease Doughnut Symptoms vs. Signs Symptoms plant s response to stress Wilting, yellowing, die-back, rings, patches, etc. Sign evidence of the causal agent Fruiting structures, people, packaging material, mold, etc. Washington State University Extension Symptoms Color Changes-Chlorosis Chlorosis: Yellowing of normal green tissue; PATTERN of discoloration helpful; Many causes General yellowing of leaf or plant; nutrient deficiency, root problems, nematodes Interveinal yellowing of leaf tissue between veins; poor root function, root rot, nematodes, nutrient deficiencies, improper ph, chemical injury, virus Color Changes- Chlorosis Along the vein Yellow along the vein; virus, some herbicides Marginal yellowing of leaf edges; chemical injury, nutrient toxicity Mosaic, Mottle irregular light and dark green areas on leaves; distinct (mosaic) less distinct (mottle); commonly viruses, genetic abnormalities, nutrient deficiency (mottle) Color Changes - Chlorosis Ring spot circular area of chlorosis and necrosis with green center; virus, cold water (African violet) 3
Other Color Changes - I Breaking: Abnormal streaks of different color in colored areas (esp. flowers); virus, genetic Purple, reddening: Abnormal purple or red color in normally green tissues; phosphorus, boron deficiency, some herbicides, other Bronzing: gold or copper metallic appearance; insects, mites, cold injury Other Browning: turns brown, brittle and dry, tissue death; Many causes Russeting: superficial roughening of skin due to cork formation; some fungus (powdery mildew); frost, some chemicals Necrosis Spot: necrotic areas on leaves, superficial lesions, round, angular, irregular, concentric rings or surrounded by purple ring or chlorotic halo; commonly fungus, bacteria, abiotic (paraquat drift), uncommonly virus or nematodes Blight: general killing of plant parts; Many Necrosis continued Blotch Large, superficial discolored areas of irregular shapes- leaves, stems fruits, stems; fungi, bacteria, chemical injury, sun scald Scorch, Marginal Necrosis Burning of leaf margins; drought, excess salt, root problems, cankers, vascular fungi, bacteria Rot tissues discolor, disintegrate (decay) & soften esp. wood rot (fungal) & root rot (usually fungal); fungi, bacteria Necrosis Canker: Necrosis area, surface may be smooth or rough, sunken with margins raised, raised margins, target shaped; usually fungi, some bacteria Necrosis Dampening off seed, seedling rot or canker like girdling seedlings causes plants at ground-line to fall over and rot; usually fungi, insects, soil conditions Shot hole (shotgun) dead areas fall away leaving holes in leaves; fungi, bacteria, virus, insect feeding, hail 4
Necrosis continued Dieback twigs, limbs, shoots dieback from tip; see blight Anthracnose small blister on the lesion surface; fungi Water soak translucent cells fill with water; bacteria, fungi, frost Miscellaneous Dwarfing/Stunting part or all plant does not reach normal size Gall, tumor, knot localized enlargement of plant parts (esp. root gall, crown gall, leaf gall); some fungi, bacteria, virus, nematodes, many insects, some mites Witches broom dense, broom like clustering of branches; phytoplasms, fungi, some mites Miscellaneous. Leaf curl irregular growth; virus, some fungi, herbicides, ethylene, aphids Wilt parts limp from lack of water; drought, root rot, root damage by nematodes, other root problems, vascular pathogens fungi, bacteria Leaf drop, abscission dropping off of leaves, fruit, flowers; leaf spot pathogens, root pathogens, various abiotic conditions Miscellaneous continued Epinasty bending down of leaves, abnormal petiole growth; vascular wilt, ethylene, some herbicides Gummosis production of thick, gummy liquid in response to injury or disease; insect, fungal, bacterial infection Mildews gray, whitish growth of fungus powdery (most common) downy Signs 5
Molds Many colors, commonly gray, white, black, blue or green, similar to mildew but from a different group of fungi Sooty Mold black fungal growth, sooty mold from excretions of sucking insects- aphids, whiteflies, scale Rust Spore pustules may be yellow, red, brown or black Smut spore masses, brown or black and powdery Mushrooms Large fruiting bodies, few are pathogens Conk large, woody shelf like fruiting body 6
Bacterial Ooze or Slime Drops of sap containing bacteria Bacterial wetwood/slime flux What Problems will you see when you talk to home owners? Problems in Ornamentals, Symptoms, Signs and Pictures Rose Black Spot Symptoms Small, Round spots 1/16 to ½ diameter Upper sides of leaves Adjacent tissue turns yellow Eventually whole leaf turns yellow and prematurely falls Yes, Even Knockouts! Rose Rosette Disease Elongation of New Shoots Witches Broom Distorted Flowers Red Pigmentation Hyperprickliness Boxwood: Phytophthora Root Rot Symptoms Poor growth and off color foliage Leaves light green turn yellow, bronze, strawcolored Leaves turn upwards, lateral leaf margins roll inward May appear on a few branches to entire plant ACES.edu 7
Boxwood Blight English Boxwood Decline Defoliation usually starting at the base of the plant Large, diffuse, dark brown leaf spots Blackened twigs and stems Root balls: Fibrous roots due to decline; Plant in middle healthy Foliage discolored and dying back Boxwood: Nematodes Root damage caused by Ring, lesion, spiral nematode Feeding damages roots Fungus can enter boxwood through damage Rootknot nematodes Meloidogyne spp. Rootknot nematodes Meloidogyne spp. Boxwood: Foliar and Stem Diseases Dieback from Volutella Blight Fruiting bodies of Macrophoma Leaf Spot 8
Powdery Mildew Powdery Mildew on Crape Myrtle Dogwood: Spot Anthracnose Symptoms Circular lesions with purple borders Powdery Mildew on Roses Spot Anthracnose on Leaves Spot Anthracnose on bracts of flowering dogwood Dogwood: Discula destructiva Symptoms Fungus not only causes leaf and bracet damage but also dieback Margins of spots are purplish in color Lower branches die first Trunk Canker Lower Branch dieback Dogwood: Septoria Leaf Spot Angular, dark spots with purplish margins, bordered by leaf veins Late season disease, appears early July in VA, become severe in late summer Can be confused wit Discula, but spots are more uniform Crown Gall Common in Euonymus Other species: cypress, hibiscus, lilac, flowering peach, privet, viburnum, and willow are susceptible Positioned at wound site Interfere with water and nutrient transfer Fire Blight in Ornamentals Blossoms and leaves wilt suddenly and turn dark brown to black, shrivel and die Blackened petiole stay attached Crabapple Bradford Pear 9
Sudden Oak Death (Phytophthora ramorum) Trees: Shade and Fruit New Disease in US, prompted USDA to quarantine counties in CA and OR First described: Germany and Netherlands 2001 Was diagnosed in Virginia 2003 Hosts Map: USDA- Forest Service Thousand Canker Disease States Confirmed and Quarantined Thousand Cankers Disease 2011 July 21, 2011 2 black walnut in Chesterfield with TCD And VDACS imposes temporary quarantine Quarantine prohibits the movement of all walnut plants, parts, logs, stumps, firewood, roots, branches, mulch and chips out of quarantined area Chesterfield, Fairfax, Goochland, Hanover, King and Queen, King William, New Kent, Powhatan and Prince William Cos., and cities of Colonial Heights, Fairfax, Falls Church, Manassas, Manassas Park and Richmond Confirmed TCD 10
TCD positive locations 8/12/11 Disease cycle & Symptoms Localized death of phloem Inoculation by walnut twig beetle Yellowing and thinning of crown Successively larger stems affected Death Cumulative effect Within 3 years of crown symptoms Thousand canker disease Black walnut and Butternut Lethal to black walnut Arizona, English, California Variable susceptibility Circa 2003 (???) Probably much older Fungus-insect complex Geosmithia morbida Pityophthorous juglandis (walnut twig beetle) Pathways Cankers caused by Geosmitha morbida Raw wood Logs, packing material, firewood Nursery stock Natural dissemination 11
What can be done? No effective insecticides No effective fungicides Quarantines only minimally effective Fungus Sooty Mold Most grow on excrement on sucking insect, aphids, scales, mealy bugs and whiteflies Does not penetrate leaf or bark tissues Indirectly a problem to plants as excludes sunlight and therefore interferes with photosynthesis Sooty mold on Walnut Sooty Mold: Hardwood or Conifers Sooty mold on beech Sooty mold on White pine Verticillium Wilt on Shade Trees Fungus enters through the roots Spreads upwards Interferes with water movement and other plant functions Problems accentuated by drought, inadequate nutrition, poor drainage, other conditions that decrease tree vigor 12
Fire Blight Problems with fruits and vegetables: Symptoms and pictures Ornamentals and fruits Infected fruit becomes leathery Cankers form on limbs, shrunken, dark brown to purplish in color Dark streaking of the wood Shepherd s crook Cucurbits: Powdery Mildew White powdery mass on leaves, petioles, young stems Can cover an entire leaf in a few days Bad infections leaves turn yellow to brown to shrivel Reduce both number and size of fruit Powdery mildew on a pumpkin leaf Cucurbits Include Pumpkins Cantaloupe Squash Cucumbers Pickling Slicers Burpless Corn Smut Obvious on ears, but may also form on leaves, tassels, and stalks, Galls are enclosed by a silvery membrane Mature, membrane breaks and black powdery spores are exposed Galls can be several inches in diameter Bacterial Spot of Pepper Plants infected in seed bed have small, irregular black or watersoaked spots on edges of 1 st leaves Older plants; small, pale green, water-soaked lesions Spots surrounded by yellow halo Center may dry and tear, giving a gunshot appearance Leaves may drop off while green Young seedling may lose topmost leaves 13
Blossom End Rot: Tomato Brown water soaked end rot Discolored area increases in size Shrunken, concave, black, leathery spot on blossom end Tomato: Early Blight Dampening off in seedbed Usually small, irregular brown spots form on older, lower leaves Spots may enlarge to up to ½ inch Concentric rings or ridges form a target pattern Can appear later in season Tomato Spotted Wilt Broccoli : Wire Stem No Cure Thrips vector the Virus Infected plant need to be removed Thrips need to be controlled Dark water soaked lesion Grow poorly, stunted Eventually die Those that do survive perform poorly and rarely have marketable head Cabbage: Bottom Rot Lower side of the head Lesions sunken, black sharply elliptical with long side of lesion parallel to mid rib Black decay at base of head Diagnosing Abiotic Disorders 14
What are Abiotic Disorders? Normal function of a plant that is affected by non-living stresses. Environmental/temperature extremes Soil properties/ph Chemical or salt injury Mechanical damage What are Abiotic Disorders? Biotic Disease vs. Abiotic Disease aka Physiological Disorders Injury or symptoms we see is ultimately due to the cumulative effects of the causal factors on the physiological processes needed for plant growth and development Cumulative Subtle Can be difficult to diagnose How do you tell the difference? Ask a lot of questions Observe environmental clues Take note of site history Biotic Diseases Usually scattered or randomly distributed Abiotic Diseases Typically appear in patterns or display uniformity Plant Diseases Top 10 Abiotic Factors Nutrient Deficiencies Nutrient Deficiencies Planting Depth Girdling Roots Mechanical Damage Packaging Material Excessive Irrigation Summer Scorch Herbicide Damage Winter Damage Environmental Pollutants Symptoms vary depending on nutrient Older leaves vs. newer leaves Interveinal chlorosis, leaf coloration, marginal burning, etc. Causes: High ph (alkaline), low ph (acidic), compacted soils, saturated soils, excessively dry soils Identifying No evidence of insect, disease signs or specific symptoms 15
Symptoms of Nutrient Deficiencies Younger leaves Older Leaves Iron chlorosis on maple blueberry Older Leaves Potassium deficiency Older leaves Manganese deficiency on maple Phosphorus deficiency Planting Depth Symptoms: No visible root flare at soil surface The trunk descends straight into the soil with no flare Leaves and annual growth are smaller than normal Early fall color and leaf drop Dieback in the crown of the tree Sparse amount of foliage Causes Repotted nursery stock Depth of planting hole is too deep Buried root flare on B&B trees Girdling Roots Symptoms: May be visible at the surface Excavation of soil at trunk base may reveal girdling roots Leaves smaller than normal Early fall color and leaf drop Dieback in the crown of the tree Sparse amount of foliage Causes: Containers Planting hold width to narrow Root bound nursery stock Mechanical Damage Symptoms: Slow growth rate Dieback above damage Sunken or sloughing bark Signs of visible damage Causes Improper pruning techniques Lawn mower/string trimmer damage Animals Heavy equipment Vandalism Packaging Material Symptoms: Slow growth rate Gradual decline in plant health Visible signs of packaging material Death Causes: Nursery tags, wire baskets, twin, burlap, and containers in ground or plants rooted through pot to ground Excessive Irrigation Symptoms Poor root establishment Gradual decline of plant Wilting Iron chlorosis Root rot problems Weak or stunted growth Can be mistaken for drought stress Causes Excessive irrigation Compacted/clay soils Poor drainage 16
Drought and Heat Symptoms Mortality Wilting Curling of leaves and conifer leaders Reduced growth (even before visible symptoms) Imposed dormancy resulting in possible out-of-season flowering Sunburned leaves Scenario Moderate stress leads to stomata closing Stomata closing leads to reduced photosynthesis and reduced transpiration (less cooling effect) Reduced transpiration can lead to leaf scorch Reduced photosynthesis leads to reduced growth Summer Scorch Symptoms Browning of leaf margins Reduced vigor late season Damage increases with heat May cause brown inter-veinal spotting Target rings Causes Dry, hot summer winds Found more on larger leaves Poorly watered trees Herbicide Damage Types of Cold Damage Symptoms Curling or cupping leaves Prominent veins Interveinal discoloration Elongated stem growth Causes Broadleaf weed killer misuse Temperature, wind, concentration Soil sterilant damage Low Temperature Injury (cold damage) Sunscald and frost cracking Winter desiccation and Freeze injury Snow and ice Cold Damage Above Freezing, low enough to cause injury Varies by species houseplants vs. landscape Symptoms Wilting Desiccation Water-logged areas Physical distortion of plant parts Winter Desiccation/Freezing Injury Plants subjected to sub-freezing temps Symptoms Discoloration or bronzing of foliage Brown needles or leaves in the spring Excessive needle drop Blackening of leaves Dieback of twigs and small branches Causes Dry winter winds Inadequate moisture for evergreens Young thin bark subject to freezing temp fluctuations Pruning issues 17
Sunscald and Frost Cracking Environmental Pollutants Result of interaction of light and temperature Caused by thawing and freezing due to a rapid fluctuation in stem temps Exposure to afternoon sun (from southwest) causes increase in stem temps and subsequent thawing of stem/trunk moisture Sun sets and temps drop rapidly below freezing will result in possible ice crystals rupturing internal tissue Sunscald will result in a sunken area of bark Frost cracking results in vertical splits Salt Damage Symptoms Brown needles on new growth Drought stress in appearance Leaves scorch as they emerge Causes Excessive salts from de-icing materials Over-fertilization Containers watering inadequately Environmental Pollutants Pesticides Symptoms (depends on variety of variables) (can be similar to nutrient disorders) Leaf chlorosis Marginal and/or spotted necrosis Total leaf necrosis Causes Misuse of pesticide (concentration, application rate) Temperature, wind, humidity Plant species Other Causes of Abiotic Disorders Wildlife/Animal Problems Deer scraping tree bark, eating plants, dog spraying, etc. Use DGIF for Nuisance Wildlife link at website Wind Damage/Hail Plant structure, tree topping Soil Compaction From equipment, cars Root damage Installation of irrigation or drainage Mulch volcanoes Resources Resources Manual of Woody Landscape Plants by Michael Dirr Abiotic Plant Disorders, Symptoms, Signs and Solutions: A Diagnostic Guide to Problem Solving by Schultzki and Cregg of Michigan State Abiotic Disorders of Landscape Plants: A Diagnotic Guide, Costello, et al., Univ. of CA Top 10 Abiotic Diseases of Woody Ornamentals by Gunnel and Goodspeed of Utah State (modified) Virginia Pest Management Guide Virginia Cooperative Extension website: http://www.ext.vt.edu http://www.ento.vt.edu/bughunt http://www.vtpp.ext.vt.edu Books in office Pesticide Management Guide Ortho Problem Solver Publications Experience of Agents and other VCE Master Gardeners 18
Summary Thanks to: Ask questions Know basics of the plant and diseases Use resources Lab Books Agents Other Master Gardeners Cynthia Gregg, Extension Agent, Brunswick County Mike Likins, County Agent, Chesterfield County 19