White Mold of Vegetables and Ornamentals
PP-899, Reviewed July 1996
Cynthia L. Ash, Diagnostician
White mold or Sclerotinia disease caused by the fungus Sclerotinia sclerotiorum causes a wilt, rot and blight of over 374 ornamentals, field crops, weeds and vegetables in 64 plant families (Table 1). Susceptibility to the white mold fungus varies considerably among these plants from a hardly noticeable infection to complete destruction. Unfortunately, those plants which are only slightly susceptible may build up the fungus in the soil. Then when a very susceptible crop such as cabbage or petunia is planted and conditions are favorable, severe disease losses result.
White mold is one of the most destructive diseases on sunflower and dry beans that farmers experience in the Northern Great Plains. In recent years this disease has been increasingly reported in flower beds and gardens in North Dakota and in 1985 destroyed large areas in flower beds on the North Dakota State University campus and the state capitol grounds.
Figure 1. White mold
of petunia in flower bed.
Symptoms
The white mold fungus can cause a blighting or rotting of any above ground OR below ground plant parts. Initially, infected plants are distributed randomly throughout the flower bed or garden. At first the affected area of the plant takes on a dark green greasy or water-soaked appearance. On stems the lesion may be brown to gray in color. If the humidity is high a white fluffy mycelial (mold) growth appears (Figure 4). Lumpy areas appear in this white growth which become hard and black as they mature. The lesions continue to develop and may spread down and up the plant from the initially infected flower, leaf, or petiole and eventually consume the entire plant. As the disease progresses the stem is girdled and the plant begins to wilt and eventually dies. Hard black bodies called sclerotia are formed inside the stem or on the outside surfaces of the stem and other plant parts (Figures 3 and 5). These are the reproductive structures of the fungus and are 1/16-1/2 inch in diameter, irregularly shaped and white to tan in the center when cut open.
The disease can continue to spread throughout the bed if the weather stays cool and moist and air movement is restricted. In the case of vegetables the disease can continue to spread under improper storage conditions and can quickly destroy the stored crop.
Disease Cycle
White mold persists in the soil as black sclerotial bodies for many years. These sclerotial bodies are directly responsible for infecting subsequent crops grown in the area. Sclerotia on or near the soil surface germinate to form one to several stalks with funnels on the end called apothecia. Apothecia are like tiny mushrooms (Figure 2). They produce spores which are forcibly injected into the air and carried by the wind for up to a mile or more. If they land on susceptible plant parts infection will occur when there is ample moisture and temperatures are cool (40-85 F). Initial infection occurs on dead plant tissues such as dead blossoms and becomes established. The fungus then invades healthy green tissues causing a soft rot. The white mycelial growth is visible within a few days and the black sclerotial bodies are present in 10-14 days thus completing the life cycle of the fungus.
Figure 2.
Apothecia (side view). About 3 times normal size.
Figure 3. Sclerotia
from sunflower head (top) soybean stem (right) pinto bean (bottom) and sunflower stalk
(left).
Figure 4. Mycelium
and sclerotial bodies on a zinnia stem.
Figure 5. Black
sclerotial bodies on zinnia stem.
Control
- Plant in well drained soil using proper spacing to prevent crowding. Avoid areas with poor air circulation. Water early in the day and deeply; avoid frequent light watering.
- If the soil is infested in a small area of the garden, remove as much of the soil as possible and replace with a clean soil.
- CAREFULLY remove all infected plants as soon as possible. Do not compost or use for mulch. Burn if possible.
- A barrier material such as plastic laid over the affected ground prevents the dispersal of spores from germinating sclerotia.
- Control weeds. Many weeds are hosts to the white mold fungus when ornamental hosts are not present. Rotate away from susceptible crops for at least 3-4 years if white mold has been found in the garden.
- Store plant materials under cool, dry conditions in a clean storage area. Store only mature blemish-free plant material which has been properly harvested and cured.
- Fungicides are available for some types of plants and situations. They act to prevent infection and will not get rid of an existing infection or destroy the sclerotia in the soil. Contact your County Extension Agent or the Plant Pest Diagnostic Lab at NDSU for more information on currently available fungicides.
Table 1. Plants Susceptible to Sclerotinia scleroriorum.
-------------------------------------------------------------------- Aconite Endive Okra Acrodium Escarole Onion Alfalfa or lucerne Eucalyptus or gum Orange (common or Alkanet Euonymus sweet), Mandarin, Almond Evening-promise (sour or Seville) Amaranthus False-dragonhead Pak-choi Anemone (poppy) Fennel Pansy Angelica Fenugreek Parsley Anise Fig (cultivated, Parsnip Apple magnolia-leaf) Papaw Apple-of-Peru Fireweed Pea (field, garden) Apricot Firewheel Peach Artichoke Flax (common, Peanut Asparagus flowering) Pear Asphodel Forget-me-not Pelargonium Aster Forsythia Pennycress (field) Avocado Foxglove Peony Babysbreath Freesia Pepper (chilli, red or Bachelors-button Fuchsia sweet) Banana (Cavendish, Gaillardia Peppergrass common) Galinsoga Peppermint Barberry (small-flowered) Periwinkle (common, Barley (winter) Garden cress Madagascar) Basil Garlic Pe-tsai Bean (Adzuki, black Gayfeather Petunia (garden, wild) gram, civet, kidney, Gazania Phlox or dwarf, lima, Gentian Pigeonpea mung, pinto, Geranium Pigweed (rough) scarlet, runner) (fish, florists') Pine (Japanese red) Begonia Gerbera Plantain (common) Bellflower (chimney Gherkin (West Indian) Plum (American, garden and willow) Ginseng (American) or prune) Birdsfoot-trefoil Gladiolus Poinsettia Bittercress Globeflower Poison-hemlock Black-salsify Gloxinia Poppy (California, Bleeding heart Goldenbells opium) Bluebells Goldenglow Potato Bristlegrass (green) Goldenrod Primrose Broadbean or vetch Gourd (yellowf lowered) Proboscis flower Broccoli Goutweed Pummelo Broomrape Granadilla Pumpkin Brussels sprouts (purplef lowered) Purslane (common) Buckhorn Grape (European wine) Pyrethrum (common, Buckwheat Grapefruit dalmatian) Burclover or toothed Groundnut or wildbean Quickweed medic Groundsel (ragwort) Radish (garden, wild) Buttercup Guayule Ragweed (Persian, wild) Hebe Rape Butterfly-flower Hedgemustard (tall) Rape (bird) Cabbage Hemp Raspberry (red) Calendula Henbane Rhubarb Camellia Heuchera Rocket-salad Candytuft Hibiscus (Chinese) Rock melon Cantaloupe Hollyhock Rose Canterbury-bells (Antwerp, common) Roselle Cape-gooseberry Hop (common or Rutabaga (swede) Cape-marigold European) Safflower Caraway Horsechestnut Sage Carnation Horseradish Salsify Carrot Houndstongue Scabious (sweet) Castorbean Hyacinth Shepherds-purse Cauliflower Hydrangea Slipperwort Celeriac Iris (English, Snapdragon Celery German, Siberian) Soybean Charlock Jamaica sorrel Sowthistle Chickpea or Jerusalem-artichoke Spiderflower garbanzo bean Jute Spikenard Chickweed (common) Kale Spinach Chicory Kale (tree) Spurge (thyme-leaved, China-aster Kenaf Kohirabi toothed) Chinese cabbage Lambsquarters Squash (summer, winter) Chinese gooseberry Larch (Japanese) Stephanotis Chokeberry (red) Larkspur (bouquet, Stock (common, Chrysanthemum candle, garland, rocket) intermediate) Cineraria (florists') Lawson cypress Strawberry Citron Lemon Strawflower Cleavers, Goosegrass Lentil Sugar-apple Clover (alsike, Lettuce (head, leaf, Sunflower crimson, Egyptian, prickly Romaine) Sunn-hemp holy, least hop, Lilac (common) Sweet alyssum red, sierra, sub- Lily (Easter, Madonna) Sweetclover (annual yellow, terranean white, Lime yellow, white) zigzag) Lobelia (edging) Sweetpea Cockscomb Lotus species Sweet potato Columbine Lupine (blue, European Sweet sultan Colza blue, sundial, Tansymustard Coriander Washington) Teasel (common, Corn chamomile Malvaviscus Fuller's) Cornflower Mangel Thistles Corn salad Marigold Tickseed Cosmos (common) Matilija-poppy Toadflax Cow-parsnip Medic (black) Tobacco (common, flowering, Cowpea or black-eyed Milk-thistle wild) pea Milkvetch Tomato Crabapple Milkweed Tree-tomato Crabgrass Monarch of the Veld Tulip Crownvetch Monkshood (azure) Turnip Cryptomeria Mountain-bluet Udo Cucumber Mouse-ear cress Valerian (common or Cynoglossum Mulberry (white) garden-heliotrope) Cypress or whitecedar Mullein (moth) Vetch (common, hairy) (Lawson) Muskmelon Wallflower Dahlia Mustard (black, leaf, Watercress Daisy (African, E white) Watermelon nglish, oxeye, Myoporum Wild chamomile Shasta, Swan river, Narcissus Wild ginger Transvaal) Nasturtium (garden, Wild mustard Dandelion wild) Wintercress (common, Russian) Nemesia Yardlong bean Deadnettle Nettle Yellow rocket Delphinium New Zealand spinach Zinnia Dill Nightshade (beaked Dock (yellow or or buffalo-bur, curled) silverleaf) Dutchman's-pipe Oak Eggplant Oats --------------------------------------------------------------------
Adapted from Sclerotinia Disease, White Mold or Watery Soft Rot, Illinois Cooperative Extension Service Circular #1008.
PP-899, June 1986
Reviewed July 1996
