WALNUT WILT Walnut wilt is a noninfectious disease which causes the sudden wilt and death of many plant species. The problem occurs in the beds of sensitive plants growing near walnut trees: Juglans negia and J. nigra; butternut: J. cinerea and J. sieboldiana; hickories: Carya ovata, C. alba, and C. olivaeformis; and Pterocarya causcasica. The cause is an active compound known as juglone produced by these trees. Juglone has been isolated from the roots, leaves, bark, and husks. The compound can also be found in a narrow zone in the soil surrounding the living roots. Because of this limited distribution of the toxin, the position of juglone producing roots underground is reflected in the pattern of wilting plants above ground. Poisoning occurs only when the roots of sensitive plants grow into the toxic zone near a juglone-producing root. Poor drainage may play a role even when roots do not actually touch. Symptoms may appear at any time during a growing season. Affected plants wilt suddenly and often show a browning of the vascular tissues just under the outer layers of the main stem. These symptoms may be easily confused with those of the vascular wilt diseases such as Fusarium and Verticillium. Some plants with mild tolerance may show stunting, lack of flower development, and/or lack of vigor. Toxicity does not occur every year. Juglone does not persist in the soil over winter. It is produced only by living walnut, butternut, and hickory juglone producing roots when they are active during the growing season. Apparently, the production and release of juglone is influenced by the growing conditions of a particular year and in some years the toxin is not produced in sufficient concentrations to become toxic to sensitive plant species. Walnut wilt can be avoided by planting vegetables or ornamentals outside of the toxic root zone. Plants will usually be safe if they are planted at a distance from the tree equal to the height of the tree. In cases where a juglone producing tree is removed, sensitive plant species may be safely planted on the site one year after the death of the tree. Juglone will not persist in dead roots or in the soil surrounding the dead roots for more than a few months following the death of the original tree. Recommendations: Don't plant the juglone producing trees in urban areas. If they are there, plant tolerant species under them. Keep in mind that the roots can spread 50 to 60 ft. from the trunk. This may be well beyond the drip line. Plants particularly sensitive to juglone include: tomato, potato, pea, cabbage, pear, apple, sour cherry, red pine and rhododendron. See the table below for a list of plants unaffected by juglone. Table 1: PLANTS SEEMINGLY TOLERANT TO JUGLONE Scientific name Common name Herbaceous Perennials: Ajuga reptans bugleweed Alcea rosea hollyhock Anemone blanda windflowers Araceae Jack-in-the-pulpit Asarum europaeum European wild ginger Astilbe Campanula latifolia bellflower Chrysanthemum hardy chrysanthemum Dicentra Bleeding-heart Doronicum leopard's bane Dryopteris cristata crested wood fern Echinacea purpurea purple coneflower Erythronium dog's tooth violet Galium odoratum sweet woodruff Geranium robertianum herb Robert G. Sanguineum cranesbill Helianthus tuberosus Jerusalem artichoke Hemerocallis fulva common daylily Heuchera xbrizoides 'Pluie de Feu' coral bells Hieracium aurantiacum orange hawkweed Hosta Forunei 'Glauca' plantrain lily H. lancifolia H. marginata H. undulata 'Variegata' Hydrophyllum virginianum Virginia waterleaf Iris siberica Siberian iris Lobelia siphilitica great blue lobelia Monarda didyma bee balm M. fistulosa wild bergamot Oenothera fruticosa sundrops Onoclea sensibilis sensitive fern Osmunda cinnommea cinnamon fern Phlox paniculata summer phlox Podophyllum emodi may-apple Polemonium reptans Jacob's ladder Polygonatum commutatum great Solomon's seal Polystichum acrostichoides Christmas fern Primula xpolyantha polyanthus primrose Pulmonaria lungwort Ranaunculus verticillatum pilewort Sanguinaria canadensis bloodroot S. canadensis 'Multiplex' double-flowered bloodroot Sedum acre gold moss S. spectabile Stachys byzantina lamb's ear Thalictrum meadow-rue Tradescantia virginiana spiderwort Trillium cernuum nodding trillium T. grandiflorum wide wake-robin Uvularia grandiflora big merrybells Viola canadensis Canada violet V. sororia woolly blue violet Bulbs: Chioniodoxa lucilae glory-of-the-snow Crocus Endymion hispanicul Spanish bluebell Eranthis hyemalis winter aconite Galanthus nivalis snowdrop Hyacinthus 'City of Harlem' Muscari botryoides grape hyacinth Narcissus 'Cheerfulness', 'Yellow Cheerfulness','Tete a Tete', 'Sundial', and 'February Gold' Scilla siberica blue squill Tulipa Darwin 'White Volcano' and 'Cum Laude' Parrot 'Blue Parrot', Greigii 'Toronto' Trees: Acer palmatum Japanese maple A. palmatum 'Dissectum', cutleaf Japanese maple Carya hickory Catalpa bignoiides common catalpa Crataegus Hawthorn Cydonia oblongata quince Diospyros persimmon Juniperus virginiana red cedar Malus sylvestris crabapple Platanus Sycamore Osmanthus Autumn olive Philadephus mock orange Quercus oaks Thuja Arvorvitae Tsuga canadensis Canadian hemlock Ulmus elm Vines and Shrubs: Cercis canadensis redbud Clematis 'Red Cardinal' Daphne mezereum February daphne Euonymus Euonymus Forsythia suspensa Weeping forsythia Hibiscus syriacus rose of Sharon Lonicera tatarica Tartarian honeysuckle Parthenocissus quinquefolia Virginia creeper Rhododendron periclymenoides pinxterbloom R. Exbury hybrids 'Gibraltar' and 'Balzac' Rhus radicans poison ivy Rubus occidentalis black raspberry Syringa lilacs Viburnum most viburnums Vitis grape Annuals: Begonia fiberous cultivars and tuberous cultivar 'Nonstop' Calendula officinalis pot marigold Heleborus cvs Christmas Rose Ipomoea 'Heavenly Blue', morning glory Viola cornuta horned violet V. xwittrockiana pansy Zinnia elegans zinnia Weeds: Glechoma hederacea ground ivy Oxalis corniculata creeping lady's sorrel Pachysandra pachysandra Stellaria media chickweed Trifolium repens white clover Taraxacum officale dandelion Veronica filiformis creeping veronica Grasses: Festuca elatior tall fescue Ophiopogon lily turf Poa pratensis Kentucky Bluegrass Vegetables and Herbs: Allium onions Beta beets Daucus carota carrot Gentiana asclepiadea gentian Gentiana septemfida gentian Pastinaca sativa parsnip Phaseolus vulgaris bean, snap beans Phaseolus lunatus lima bean Zea mays corn Sources: Black Walnut Toxicity, Summary of Ontario Ministry of Agriculture and Food, AGDEX 246180, November 1984. Michigan State University Extension Home Page, 7/97, Walnut Toxicity 7/97 Revised By Faith Harrison and Diane Karasevicz Diagnostic Lab Extension Associate Assistant