Verticillium Wilt
Click for larger image Redbud (Cercis) wilted and died within a week from verticillium wilt

Verticillium wilt is a fungal disease of over 300 host plants, including a wide range of garden and greenhouse crops in addition to woody ornamentals, most noticeably elms, magnolias, maples, redbud, and viburnums. (See following list for a more complete list of susceptible plants.) Caused by the soil-borne pathogens Verticillium dahliae and V. albo-atrum, these wilts are prevalent throughout the tropical and temperate regions of the world. They exist in the soil primarily as mycelia that infect belowground plant tissue. High summer temperatures tend to halt development of the disease. Groups of plants resistant to verticillium wilt include gymnosperms, monocots, members of the rose family, oaks, dogwoods, willows, rhododendrons, azaleas and others.

Symptoms and Diagnosis

Symptoms of verticillium wilt vary somewhat in different host species and also within species due to varying environmental conditions. These might include sudden wilting of small branches, yellowing of foliage, stunting of growth and premature defoliation. Sapwood of infected branches typically has olive-green to black streaks. Vascular tissue appears as a dark ring in cross sections or pin-point dark spots. The initial symptoms may occur on only one branch or may involve the entire plant. Oddly, following the initial symptoms, there may be no sign of the disease for several years, even though the infection continues to reduce plant vigor.

Life Cycle

Verticillium species are opportunistic fungi that persist in the soil as saprophytes. The organism overwinters as mycelia or microsclerotia a dark, condensed mass of mycelium that collectively act as a propagule, which germinates under favorable conditions. Infection begins in the root area where the resting hyphae of Verticillium germinate and penetrate feeder roots. The fungus also can enter wounds in the root area. The mycelium of the fungus may grow slowly. The disease spreads within the plant by mycelium or spores called microconidea that travel in xylem vessels to other parts of the plant. Where the spores lodge, new hyphae grow and increase the infection. The infected plant tissue becomes necrotic (dead) because the vascular tissue is clogged with mycelium, conidia and by products of fungal metabolism. As a result water flow is restricted and the plant wilts. The necrotic tissue is what causes the dark streaks that are symptomatic of this wilt disease. The entire plant may die quickly or may die section by section over many years.

Integrated Pest Management Strategies

1. Sanitation. Remove affected annuals and perennials or prune damaged areas of trees and shrubs. Pruning disease-damaged branches and foliage plus increasing the vigor of trees and shrubs may help to keep symptoms checked. Be sure to sterilize pruners between cuts.

2. Plant resistant or tolerant species. This is the best way to manage this disease. Fungicides are not generally effective or practical.

Following is a list of susceptible and resistant plants taken from "Plants Resistant and Susceptible to Verticillium Wilt", Leaflet 2703, University of California.

PLANTS SUSCEPTIBLE TO VERTICILLIUM WILT

Trees
Almond, apricot, cherry, peach,
plum, prune (Prunus spp.)
Ash (Fraxinus spp.)
Black locust
(Robinia pseudoacacia)
Box elder (Acer negundo)
Catalpa (Catalpa spp.)
Elm (Ulmus spp.)
Golden rain tree
(Koelreuteria paniculata)
Maple (Acer spp.)
Pecan (Carya illinoensis)
Persimmon (Diospyros spp.)
Redbud (Cercis canadensis)
Russian olive, Oleaster
(Elaeagnus angustifolia)
Sour gum (Nyssa sylvatica)
Southern magnolia
(Magnolia grandiflora)
Tree-of-heaven
(Ailanthus altissima)
Tulip tree (Liriodendron tulipifera)
Yellow wood (Cladrastis lutea)


Shrubs and Vines
Barberry (Berberis spp.)
Blackberry, black raspberry,
brambles, dewberry, red
raspberry, and thimbleberry
(Rubus spp.)
(some cvs. resistant)
Currant, gooseberry (Ribes spp.)
Elderberry (Sambucus sp.)
Heather (Erica spp.)
Lilac (Syringa)
Privet (Ligustrum spp.)
Rose (Rosa spp.)
Rosemary (Rosmarinus)
Sacred bamboo
(Nandina domestica)
Smoke tree (Cotinus coggygria)
Sumac (Rhus spp.)
Trumpet creeper
(Campsis radicans)
Viburnum (Viburnum spp.)


Vegetables and Field Crops
Brussels sprouts (Brassica
oleracea var. gemmifera)
Cabbage
(Brassica oleracea var. capitata)
Cantaloupe, honeydew, Persian
melon, muskmelon
(Cucumis melo)
Castor bean (Ricinus communis)
Cotton (Gossypium spp.)
Cowpea (Vigna sinensis)
Cucumber (Cucumis sativus)
Eggplant (Solanum melongena)
Hemp (Cannabis sativa)
Horseradish
(Armoracia lapathifolia)
Mint (Mentha spp.)
New Zealand spinach
(Tetragonia expansa)
Okra (Hibiscus esculentus)
Peanut (Arachis hypogaea)
Pepper (Capsicum spp.)
Potato (Solanum tuberosum)
Pumpkin (Cucurbita pepo)
Radish (Raphanus sativus)
Rhubarb (Rheum rhaponticum)
Rutabaga (Brassica napobrassica)
Safflower (Carthamus tinctorius)
Salsify (Tragopogon porrifolius)
Spinach (Spinacia oleracea)
Strawberry (Fragaria chiloensis
var. ananassa)
(some cvs. resistant)
Tomato
(Lycopersicon esculentum)
( VF varieties resistant)
Watermelon (Citrullus vulgaris)
Yard-long bean
(Vigna sesquipedalis)


Herbaceous Ornamentals
African daisy (Arctotis spp.)
Alkekengi, Chinese lantern plant
(Physalis alkekengi)
American spikenard
(Aralia racemosa)
Aster (Aster spp.)
Belladonna (Atropa belladonna)
Bellflower (Campanula spp.)
Black-eyed Susan
(Rudbeckia serotinia)
Blue sage (Salvia azurea
var. grandiflora)
Butterfly flower
(Schizanthus pinnatus)
California poppy
(Eschscholzia californica)
Cape marigold
(Dimorphotheca sinuate)
China aster
(Callistephus chinensis)
Chrysanthemum
(Chrysanthemum spp.)
(many cvs. resistant)
Clarkia (Clarkia elegans)
Cockscomb
(Celosia argentea var. cristata)
Dahlia (Dahlia variabilis)
Foxglove (Digitalis purpurea)
Garden balsam
(Impatiens balsamina)
Gayfeather (Liatris spp.)
Geranium
(Pelargonium x hortorum)
Heliotrope
(Heliotropium arborescens)
Jacob’s ladder (Polemonium spp.)
Lobelia (Lobelia erinus)
Mealy-cup sage (Salvia farinacea)
Mignonette (Reseda odorata)
Oriental poppy
(Papaver orientale)
Painted tongue
(Salpiglossis sinuata)
Pelargonium
(Pelargonium x domesticum)
Peony (Paeonia spp.)
Petunia (Petunia hybrida)
Phlox (Phlox spp.)
Poppy-mallow
(Callirhoe papaver)
Rocket larkspur
(Delphinium ajacis)
Sage (Salvia haematodes)
Shasta daisy
(Leucanthemum x superbum)
Snapdragon (Antirrhinum majus)
Stock (Matthiola incana)
Strawflower
(Bracteantha bracteata)
Sweet pea (Lathyrus odoratus)
Sweet sultan
(Centaurea imperialis)
Tickseed (Coreopsis lanceolata)
Transvaal daisy
(Gerbera jamesonii)
Udo (Aralia cordata)


PLANTS RESISTANT OR IMMUNE TO VERTICILLIUM WILT

Families or Groups
Cactus family (all true cactus)
Conifers (cypress, fir, ginkgo,
larch, juniper, pine, sequoia,
spruce, others)
Fern family (all true ferns)
Grass family (Cereal grains, corn,
grasses, milo, sorghum, others)
Other monocots (bamboo,
banana, gladiolus, grasses, iris,
lily, onion, orchids, palms,
others)


Trees and Shrubs
Apple, flowering crabapples
(Malus spp.)
Bearberry (Arctostaphylos spp.)
Beech (Fagus spp.)
Birch (Betula spp.)
Box (Buxus spp.)
Ceanothus (Ceanothus spp.)
Dogwood (Cornus spp.)
European mountain ash
(Sorbus aucuparia)
Hawthorn (Crataegus spp.)
Holly (Ilex spp.)
Honey locust, locust
(Gleditsia spp.)
Hornbeam (Carpinus spp.)
Katsura tree
(Cercidiphyllum japonicum)
Linden (Tilia spp.)
Mulberry (Morus spp.)
Oak (Quercus spp.)
Oleander (Nerium oleander)
Pear (Pyrus spp.)
Plane tree, sycamore
(Platanus spp.)
Pyracantha, firethorn
(Pyracantha spp.)
Sweet gum
(Liquidambar styraciflua)
Walnut (Juglans spp.)
Willow (Salix spp.)


Vegetables and Field Crops
Celery (Apium graveolens)
Asparagus (Asparagus officinalis)
Carrot (Daucus carota)
Sweet potato (Ipomoea batatas)
Lettuce (Lactuca spp.)
Alfalfa (Medicago sativa)
Bean (Phaseolus spp.)
Pea (Pisum sativum)


Herbaceous Ornamentals
Ageratum (Ageratum spp.)
Alyssum (Alyssum spp.)
Anemone (Anemone spp.)
Baby-blue-eyes
(Nemophila menziesii)
Baby's breath
(Gypsophila paniculata)
Balloon flower
(Platycodon grandiflorum)
Browallia (Browallia spp.)
Calendula, pot marigold
(Calendula officinalis)
Candytuft (Iberis spp.)
Christmas rose (Helleborus niger)
Cleome (Cleome spp.)
Columbine (Aquilegia spp.)
Coral bells (Heuchera sanguinea)
Cup flower
(Nierembergia frutescens)
English daisy (Bellis perennis)
Evening primrose
(Oenothera spp.)
Gaillardia (Gaillardia spp.)
Geum (Geum spp.)
Hollyhock (Althaea rosea)
Honesty, silver dollar
(Lunaria annua)
Impatiens (Impatiens sultani)
Lantana (Lantana spp.)
Monkey flower (Mimulus spp.)
Moss rose (Portulaca grandiflora)
Nasturtium (Tropaeolum majus)
Nemesia (Nemesia strumosa)
Pansy, viola, violet (Viola spp.)
Penstemon (Penstemon spp.)
Periwinkle (Vinca minor)
Persian buttercup
(Ranunculus asiaticus)
Pinks, sweet William
(Dianthus spp.)
Potentilla (Potentilla spp.)
Primrose (Primula spp.)
Scabiosa, sweet scabious
(Scabiosa atropurpurea)
Sun rose
(Helianthemum nummularium)
Sunflower (Helianthus spp.)
Tuberous begonia
(Begonia tuberhybrida)
Verbena (Verbena x hybrida)
Wallflower (Cheiranthus cheiri)
Wax begonia
(Begonia semperflorens)
Wishbone plant
(Torenia fournieri)
Zinnia (Zinnia spp.)

Organic Strategies

Both of the recommended IPM strategies are strictly organic approaches.

More images:

Click for larger image
Dieback of redbud (Cercis) caused by verticillium wilt
 
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