Recognizing Death Cap mushroom

Transcription

1 Death Cap Mushrooms Death Cap mushroom, Amanita phalloides, is native to Europe and widespread there, being known from North Africa to the south coast of Scandinavia and from Ireland to Poland and western Russia. In its native range, the Death Cap fungus forms mutually beneficial symbiotic relationships, known as ectomycorrhizae, primarily with hardwoods (oaks, beeches, chestnuts, birches, filberts, hornbeams), less frequently with conifers (pines and spruces). It is the only known invasive ectomycorrhizal fungus in North America, having been introduced to North America from Europe many decades ago likely on the roots of imported trees. Death Cap mushroom is now known from both the east and the west coasts of North America, mostly though not exclusively, in urban areas with exotic boulevard trees. Death Cap mushrooms are not found in areas without trees nearby. The Death Cap mushroom contains toxins that target the liver primarily but other organs such as the kidneys are also affected. After ingestion, symptoms usually appear after a lag period of 6-12 hours and may include nausea and vomiting. The person can then start to feel better but the toxins are at work attacking vital organs. After a delay of several days the person becomes very ill, including jaundice, seizures, and coma, sometimes culminating in death; with prompt treatment in hospital the mortality rate is 10-30%. Cooking the mushroom does not inactivate the toxin. There is no evidence that simply handling death cap mushrooms is dangerous but, in an abundance of caution, we recommend that disposable gloves be worn when disposing of death cap mushrooms. The first record of Death Cap mushroom in Canada is a British Columbia collection found in 1997 in a grove of large European sweet chestnut trees in Lake Errock area near Mission. The second Canadian record was made in 1998 under a large ornamental European beech tree in landscaped grounds of a residence in Victoria, BC. In 2008 the first Death Cap mushrooms found in Vancouver were collected from under a European hornbeam street tree apparently planted in the 1960s. There are now numerous records of Death Cap mushrooms from the south-western corner of British Columbia - in the Fraser Valley, Vancouver and its neighbouring municipalities in the Fraser Delta, in and around Victoria on southern Vancouver Island, and on Galiano Island (see map). Almost all of the Death Cap locations in BC are under non-native broadleaf tree species (Table 1), however, it is now known that Death Cap can fruit in association with Garry oak. Eradication would be difficult. Removal of the host trees would get rid of the fungus as long as all of the host trees at each location are removed but the removal of big, beautiful street trees that contribute so much to the health and beauty of our cites would create many new problems for municipalities. Targeting known individual host trees in high risk areas (e.g. playgrounds, school yards), however, might be reasonable. Safe removal and disposal of the mushrooms, preferably in the button stage, would help manage the problem if municipalities are able to return to each site every few days. Where 1

2 lawns are watered, Death Cap mushroom can start fruiting in July and continue fruiting right through to the fall rains which will also bring on fruiting at non-watered locations. Municipalities and individuals can select non-host trees for new or replacement planting in parks, boulevards, and private properties. A list of host and non-host boulevard trees can be found in Table 1. However, opting to plant only non-host trees will also lead to a decline in the wonderful array of other ectomycorrhizal mushrooms that add biological diversity to our cities. Recognizing Death Cap mushroom Death Cap mushrooms emerge from the ground as small, white buttons (called primordia) about the size of small chicken eggs. At this stage, they can be mistaken for puffballs, straw mushrooms, or edible Asian Amanita species. If the primordia are cut in half from top to bottom, a very careful examination will reveal the cap, gills and stem of a tiny, developing mushroom. As it matures, the mushroom elongates and the white tissue enveloping the developing mushroom (universal veil) breaks, leaving a membranous white sac (volva) at the base of the stem that may require careful excavation to keep it intact for observation. The volva is often partially or fully buried in the soil. As the stem elongates further and the cap expands, a second white tissue (partial veil) that had covered the gills tears away under the cap edge, leaving a skirt-like veil or ring on the stem. The cap is slippery when moist but develops a satiny or metallic sheen when dry. In mature mushrooms, the cap generally has a distinctive olive or green hue, although the cap overall can appear pale green, pale brown, pale yellow or sometimes white. The cap is 4-16cm in width. The Death Cap mushroom has white gills, a white stem (or tinged with the cap s colour), a white, skirt-like partial veil or ring on the stem, and a white, membranous, sac-like volva surrounding the base of the stem. The Death Cap mushroom usually fruits in the fall, but it can fruit in the summer when yards are watered. 2

3 Button or primordium, cut from top to bottom, revealing cap and gills of mushroom inside. Photo credit: Paul Kroeger. Young expanded mushrooms showing skirt-like ring on stem (mushroom on the left) and the top of the volva (mushroom on right). Photo credit: Paul Kroeger. 3

4 Carefully excavated Death Cap mushrooms showing skirt-like ring on stem and cup or volva enveloping the base of the stem. Photo credit: Adolf Ceska. Young (left) and fully expanded (right) Death Cap mushrooms showing range of colour and form. Photo credit: Adolf Ceska. 4

5 Variations in cap colour. Photo credit: Paul Kroeger. Mostly white Death Cap mushroom caps showing satiny sheen. Photo credit: Paul Kroeger. Brown-hued Death Cap mushroom cap. Photo credit: Adolf Ceska. 5

6 Yellow-green-hued Death Cap mushroom cap. Photo credit: Adolf Ceska. Look-alike mushrooms Death Cap mushrooms emerge from the ground as small, egg-shaped, whitish buttons (called primordia). At this stage, they can be mistaken for puffballs, straw mushrooms, or edible Asian Amanita species. Young puffballs can be distinguished from Amanita buttons when cut from top to bottom, puffball internal tissue is uniform with no stem, cap or gills as seen in Amanita buttons. It has been suggested that Death Cap mushrooms are being mistaken for straw mushrooms (Volvariella volvacea) or edible Amanita species native to Asian countries (e.g. Amanita princeps and other species). Neither straw mushroom nor the edible Asian Amanita species grow in British Columbia. Left: Lycoperdon species puffball sliced open. Right: Death Cap button sliced open to reveal cap and gills of developing mushroom inside. Photo credits: Shannon Berch and Paul Kroeger. 6

7 Straw mushroom or Volvariella volvacea. Developing buttons on the right and more mature mushroom on the left. Photo credit: Fred Notzel. White Caesar mushroom or Amanita princeps. Buttons on lower right, expanded buttons on upper right, and more mature mushrooms on the left. Photo credit: Britt Bunyard. Frequently asked questions I think I have found Death Cap mushrooms. What should I do? 1) Confirm Ensure that the mushroom has all or most of these features: Cap whitish or with green, yellow or brown hues; about 4-16cm in width White gills 7

8 Skirt-like ring on stem Loose, sac-like cup (volva) at base of stem, often below ground (careful excavation is required to observe) Fruiting in the city on the ground near hardwood/broadleaf trees, often in boulevards with street trees 2) Document Take photographs of the whole mushrooms including the carefully excavated base of the stem; top, bottom and side views; and gills. Record your location (city, street address or intersection). Record the number of Death Cap mushrooms found and the tree it was found with (provide photographs of the tree and its leaves). 3) Report Go to the on-line form for reporting invasive species: Be sure to photograph the suspected Death Cap mushrooms as described above and have those images ready to provide after you have submitted the report. 4) Control If the Death Cap mushrooms are associated with boulevard trees on city property, contact your Municipality s Parks Department. They may agree to send a crew to remove the mushrooms. Or, remove all Death Cap mushrooms and buttons yourself, bag them and dispose of them in the garbage. Do not put them in the compost to avoid spreading the fungus. There is no evidence that simply handling Death Cap mushrooms is dangerous but, in an abundance of caution, we recommend that disposable gloves be worn when disposing of Death Cap mushrooms. Where did the Death Cap mushroom come from? The Death Cap mushroom is native to Europe and was likely introduced to North America accidentally on the roots of imported horticultural trees. It may have been subsequently propagated inadvertently in bare root nurseries on the roots of trees (see Table 1) and transferred to boulevards and other locations when the host trees were planted. Is this mushroom a problem in Europe? Yes. This mushroom is the cause of the most frequent and most serious mushroom poisonings wherever it is found. In its native territory, it is better known than it is here and so avoided by those who forage for mushrooms. Why is this mushroom a problem here? The presence of large numbers of these dangerous mushrooms in highly populated areas poses a high risk for accidental ingestion by people or their pets. Curious or grazing children or pets may encounter and eat them with severity of results depending on the amount ingested. 8

9 Infants or toddlers and young puppies are especially vulnerable to dire or fatal consequences. In exposures of this sort it s often difficult to establish whether, or exactly how much of, the suspect mushroom was actually ingested. Death Cap mushroom is a problem here for human health also when it is consumed by mushroom foragers. Mushroom foragers can mistake the Death Cap mushroom buttons for edible puffballs. Death Cap buttons and mushrooms can also be confused with familiar edible species from countries of origin, e.g. straw mushroom and edible Amanita species from Asia. Usually found associated with exotic hardwood trees in boulevards, Death Cap mushroom has recently been demonstrated to fruit in association with our native Garry oak. In California, Death Cap mushroom has spread to native oaks species and out of the cities into native forests where they often are the most abundant mushrooms found. If Death Cap mushroom adapts well to Garry oak and spreads out of our cities, it may displace native mushrooms that are associated with this tree. If it fruits in our Garry oak woodlands, it may surprise and confuse even experienced mushroom foragers who do not expect to find it outside of our cities. The BC invasion is the northern-most spread of this species in North America. Could it spread further and could this be related to climate change? Now that Death Cap mushroom has been found fruiting with Garry oak, it seems possible that it might spread through the range of Garry oak. It has been predicted that the current range of Garry oak in the province may expand due to climate change and if that happens, Death Cap mushroom might move with it (see map). Death Cap mushroom was first found fruiting in BC in the late 1990s. Since that time, it has been found at more and more locations (see map). In part this might be due to the heightened vigilance of members of the local mushroom clubs, especially Vancouver Mycological Society and South Vancouver Island Mycological Society, and more streets and parks being searched by them. It is also possible that the fungus existed for an extended period on the roots of host trees but only produced mushrooms once the trees get to a certain age or size. But, it seems likely that this fungus is spreading within our cities as it has in other cities it has invaded. Cities in BC with mild climates where broadleaf boulevard trees have been planted but Death Cap mushroom has not yet been reported (e.g. Kelowna, Nanaimo, Prince Rupert and more) should be carefully checked for Death Cap mushrooms. It is also possible that Death Cap mushroom will be found wherever nut trees such as sweet chestnut or filbert (hazelnut) are grown. In BC, this includes parts of southern Vancouver Island and the smaller islands, the lower Fraser Valley, and the Okanagan Valley, although it has not yet been reported from the latter location. How did this mushroom get onto my property/into my neighbourhood? 9

10 It likely came in as an essentially invisible ectomycorrhizal associate of an exotic broadleaf tree planted in the boulevard, park, or on your property. What impacts can this mushroom have on my property, in urban areas, or in natural ecosystems? Why should I worry about the arrival of this species in BC, other than because it is toxic if eaten? It has been speculated that as Death Cap mushroom spreads to native trees especially Garry oak it may outcompete native ectomycorrhizal fungi and change the community dynamics and diversity of our native mycorrhizal fungi. Research would be needed to determine if this is so. If Death Cap mushroom begins fruiting in our woodlands with Garry oak, it could pose an additional threat to mushroom foragers who might not expect to find Death Cap mushroom outside of our cities. Death Cap mushroom forms ectomycorrhizal associations with the roots of certain tree species (see Table 1); generally ectomycorrhizal associations are beneficial to the host tree so the growth of boulevard trees is likely improved by the presence of the fungus. How do I get rid of this mushroom? Death Cap mushroom forms mycorrhiza with living host trees and exists primarily as a perennial mycelium in the soil and in the roots of host trees. Removing the mushrooms will not eradicate the mycelium and it is likely that more mushrooms will form from the same mycelium in the same year and in future years. Eradication of the mycelium would be difficult. Removal of the host trees would get rid of the fungus and this might be an option for trees on private property (but check with your municipality for the bylaws on tree removal). On public lands in boulevards and parks, the removal of big, beautiful trees would likely create an outcry from the public. Replacement of host trees as they decline with non-host trees would help to control the spread of this fungus. Safe removal and disposal of the mushrooms, preferably in the button stage, would help manage the problem by getting rid of the immediate threat and perhaps by slowing spread via spores. Some municipalities have a policy of staff removing Death Cap mushrooms from known fruiting sites. Or, you could remove all Death Cap mushrooms and buttons yourself, bag them and dispose of them in the garbage. Do not put them in the compost to avoid spreading the fungus. Wash your hands with soap and running water after handling the mushrooms. Trying to get rid of Death Cap mushroom by mowing does not get rid of the part of the fungus that lives perennially on the roots of the host tree. Mowing Death Cap mushrooms might also spread the fungus by dispersing spores into the air and onto mowing equipment that then moves on to another site possibly carrying bits of the mushrooms with it. With routine mowing 10

11 of known Death Cap mushroom sites, removal of all Death Caps before mowing is recommended. Kicking, stomping or cutting off Death Cap mushrooms will not eradicate them because their mycelium lives belowground on the roots of host trees. Not watering known Death Cap mushroom sites will likely prevent its fruiting during the summer but fruiting will likely commence when the rain returns in the fall. Useful links Death Cap Mushroom Fact Sheet The real story behind increased Amanita poisonings in North America. Amanita phalloides: Invasion of the Death Cap. Bay Area Mycological Society. Report a Death cap mushroom: 11

12 Table 1. Status of boulevard trees as hosts for Death Cap mushroom (Amanita phalloides). Modified from list of preferred boulevard trees provided by the Municipality of Saanich. Known* host trees for Death Cap mushroom Common name Scientific name Hornbeam Carpinus betulus** English oak Quercus robur** Sweet chestnut Castanea sativa** Beech Fagus sylvatica** Filbert Corylus avellana** Linden Tilia species Garry oak Quercus garryana Northern red oak Quercus rubra * Demonstrated host trees in British Columbia. **Listed in rough order of number of occurrences as host tree in BC. Possible* host trees for Death Cap mushroom Common name Scientific name Birch Betula species Scarlet oak Quercus coccinea Pin oak Quercus palustris * Forms ectomycorrhizae and belongs to same genus as known host species. Common name Red maple Amur maple Paperbark maple Bigleaf maple Norway maple Pacific Sunrise maple Red horse chestnut Eastern redbud Nootka cypress Dogwood Hawthorn Glory ash Maidenhair tree Honey locust Golden rain tree Sweetgum Magnolia Non-host* trees for Death Cap mushroom Scientific name Acer rubrum Acer ginnala Acer griseum Acer macrophyllum Acer platanoides Acer truncatum x Acer platanoides Aesculus x carnea Cercis canadensis Chamaecyparis nootkatensis Cornus kousa x nuttalli Crataegus x mordenensis Fraxinus excelsior Ginkgo biloba Gleditsia triacanthos Koelreuteria paniculata Liquidambar styraciflua Magnolia species 12

13 Black Tupelo Persian ironwood London plane Ornamental cherries and plums Oakleaf mountain ash Japanese snowbell Western redcedar * These trees do not form ectomycorrhizae. Nyssa sylvatica Parrotia persica Platanus x acerifolia Prunus species Sorbus thuringiaca Styrax japonicus Thuja plicata Probably non-host trees for Death Cap mushroom Common name Scientific name Yellowwood* Cladrastis kentukea Serbian spruce** Picea omorika Douglas-fir** Pseudotsuga menziesii Scot s pine Pinus sylvestris * Mycorrhizal status not known. Some trees in same family form ectomycorrhizae. **Forms ectomycorrhizae (and spruce is a known host in Europe) but our west coast North American Death Caps thus far are reported only from broadleaf trees. 13