Post by ncboman on Jan 18, 2006 12:13:53 GMT -5
Pretty good info about walnut toxicity and the plants that can be grown under walnut trees. 
WALNUT TOXICITY
Many years ago a quinone called juglone was isolated from
the husks of Walnut. Juglone was found to be highly toxic
when injected into alfalfa and tomato plants and has even
killed apple trees growing near walnuts. Experiments have
found that a toxic effect of walnut bark causes a growth
failure of tomatoes and alfalfa within the root zone of
walnuts. There are, however, some conditions under which
these plants may grow near walnut trees without apparent
damage.
A scientific term used to describe one plant's suppression
of another through the secretion of a chemical in the
environment is Allelopathy. It has lent its name to a new
branch of science concerned with the interaction between
plants and the environment; this branch has done
considerable research in the walnut area.
Juglone is a toxic substance, a napthaquinone that has
been isolated in many plants in the Walnut family. Some
of the plants in the Walnut family containing Juglone are:
Persian walnut, J. regia, Black Walnut, J. nigra, and
Butternut, J. cinerea, J. sieboldiana, J. mandshurica.
There are some hickories which also yield juglone: the
Carya ovata, the C. alba, the C. olivae formis and the
Pterocarya caucasica.
There is often some confusion in the cause of the wilting,
as most of the symptoms are similar. Normal wilting,
caused by water deficiency, occurs when: shade and
competition for water and nutrients to some degree affect
the growth of all plants growing under Walnut. Lowering
the percentage of water in the soil affects all of the
plants with roots in the same soil profile uniformly. The
signs of water deficiency appear slowly, and can be
allayed with an addition of water to the soil. The
addition of water brings back turgor which persists until
soil water is again deficient.
Wilting caused by contact with Walnut roots occurs in a
relatively short time, even when there is ample soil
moisture. Wilting may occur on only a part of the plant,
or the whole plant may be affected. It is wise to detect
this early, as plants in the early stages may recover when
additional water is applied. Later wilting becomes more
severe, there is a browning of the leaves and wilting
usually results in the death of the plant. The observed
toxic effect of Walnut can also be partly offset by
liberal supplies of nitrogen.
This toxic affect on surrounding plants appears to be
related to root contact, as walnut hulls and leaves used
as mulch have not shown toxic effects on plant growth.
Because Walnut roots do not occupy the surface layers in
most soil, many shallow rooted plants growing under walnut
trees don't come in contact with the roots and are not
affected by them.
Tomatoes and alfalfa have been grown normally close to
young trees. This suggests that either the toxic
substance may not be formed yet in the young trees or that
the roots of the young tree are few and do not come into
contact with those of the plants beneath it.
Evidence also indicates that the toxic effect does not
remain in the soil more than about one year after removal
of a walnut tree.
A list of special cultivars that can survive under walnut
trees follows:
Herbaceous Perennials:
Ajuga reptans; bugleweed
Alcea rosea; hollyhock
Asarum europaeum; European wild ginger
Astilbe
Campanula latifolia; bellflower
Chrysanthemum; hardy chrysanthemum
Doronicum; leopard's bane
Dryopteris cristata; crested wood fern
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
Monarda didyma; bee balm
M. fistulosa; wild bergamot
Oenothera fruticosa; sundrops
Onoclea sensibilis; sensitive fern
Osmunda cinnommea; cinnamon fern
Phlox paniculata; summer phlox
Polemonium reptans; Jacob;s ladder
Polygonatum commutatum; great Solomon's seal
Primula xpolyantha; polyanthus primrose
Pulmonaria; lungwort
Sanguinaria canadensis; bloodroot
S. canadensis; 'Multiplex', double-flowered bloodroot
Sedum acre; gold moss
S. spectabile
Stachys byzantina; lamb's ear
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
Catalpa bignoiides; common catalpa
Tsulga canadensis; Canadian hemlock
Vines and Shrubs:
Clematis; 'Red Cardinal'
Daphne mezereum; February daphne
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'
Annuals:
Begonia; fiberous cultivars and tuberous cultivar
'Nonstop'
Calendula officinalis; pot marigold
Ipomoea; 'Heavenly Blue', morning glory
Viola cornuta; horned violet
V. xwittrockiana; pansy
Weeds:
Glechoma hederacea; ground ivy
Oxalis corniculata; creeping lady's sorrel
Stellaria media; chickweed
Taraxacum officale; dandelion
Veronica filiformis; creeping veronica
ref;
web1.msue.msu.edu/msue/imp/modop/00001916.html
WALNUT TOXICITY
Many years ago a quinone called juglone was isolated from
the husks of Walnut. Juglone was found to be highly toxic
when injected into alfalfa and tomato plants and has even
killed apple trees growing near walnuts. Experiments have
found that a toxic effect of walnut bark causes a growth
failure of tomatoes and alfalfa within the root zone of
walnuts. There are, however, some conditions under which
these plants may grow near walnut trees without apparent
damage.
A scientific term used to describe one plant's suppression
of another through the secretion of a chemical in the
environment is Allelopathy. It has lent its name to a new
branch of science concerned with the interaction between
plants and the environment; this branch has done
considerable research in the walnut area.
Juglone is a toxic substance, a napthaquinone that has
been isolated in many plants in the Walnut family. Some
of the plants in the Walnut family containing Juglone are:
Persian walnut, J. regia, Black Walnut, J. nigra, and
Butternut, J. cinerea, J. sieboldiana, J. mandshurica.
There are some hickories which also yield juglone: the
Carya ovata, the C. alba, the C. olivae formis and the
Pterocarya caucasica.
There is often some confusion in the cause of the wilting,
as most of the symptoms are similar. Normal wilting,
caused by water deficiency, occurs when: shade and
competition for water and nutrients to some degree affect
the growth of all plants growing under Walnut. Lowering
the percentage of water in the soil affects all of the
plants with roots in the same soil profile uniformly. The
signs of water deficiency appear slowly, and can be
allayed with an addition of water to the soil. The
addition of water brings back turgor which persists until
soil water is again deficient.
Wilting caused by contact with Walnut roots occurs in a
relatively short time, even when there is ample soil
moisture. Wilting may occur on only a part of the plant,
or the whole plant may be affected. It is wise to detect
this early, as plants in the early stages may recover when
additional water is applied. Later wilting becomes more
severe, there is a browning of the leaves and wilting
usually results in the death of the plant. The observed
toxic effect of Walnut can also be partly offset by
liberal supplies of nitrogen.
This toxic affect on surrounding plants appears to be
related to root contact, as walnut hulls and leaves used
as mulch have not shown toxic effects on plant growth.
Because Walnut roots do not occupy the surface layers in
most soil, many shallow rooted plants growing under walnut
trees don't come in contact with the roots and are not
affected by them.
Tomatoes and alfalfa have been grown normally close to
young trees. This suggests that either the toxic
substance may not be formed yet in the young trees or that
the roots of the young tree are few and do not come into
contact with those of the plants beneath it.
Evidence also indicates that the toxic effect does not
remain in the soil more than about one year after removal
of a walnut tree.
A list of special cultivars that can survive under walnut
trees follows:
Herbaceous Perennials:
Ajuga reptans; bugleweed
Alcea rosea; hollyhock
Asarum europaeum; European wild ginger
Astilbe
Campanula latifolia; bellflower
Chrysanthemum; hardy chrysanthemum
Doronicum; leopard's bane
Dryopteris cristata; crested wood fern
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
Monarda didyma; bee balm
M. fistulosa; wild bergamot
Oenothera fruticosa; sundrops
Onoclea sensibilis; sensitive fern
Osmunda cinnommea; cinnamon fern
Phlox paniculata; summer phlox
Polemonium reptans; Jacob;s ladder
Polygonatum commutatum; great Solomon's seal
Primula xpolyantha; polyanthus primrose
Pulmonaria; lungwort
Sanguinaria canadensis; bloodroot
S. canadensis; 'Multiplex', double-flowered bloodroot
Sedum acre; gold moss
S. spectabile
Stachys byzantina; lamb's ear
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
Catalpa bignoiides; common catalpa
Tsulga canadensis; Canadian hemlock
Vines and Shrubs:
Clematis; 'Red Cardinal'
Daphne mezereum; February daphne
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'
Annuals:
Begonia; fiberous cultivars and tuberous cultivar
'Nonstop'
Calendula officinalis; pot marigold
Ipomoea; 'Heavenly Blue', morning glory
Viola cornuta; horned violet
V. xwittrockiana; pansy
Weeds:
Glechoma hederacea; ground ivy
Oxalis corniculata; creeping lady's sorrel
Stellaria media; chickweed
Taraxacum officale; dandelion
Veronica filiformis; creeping veronica
ref;
web1.msue.msu.edu/msue/imp/modop/00001916.html
