Chapter Seventeen

MAJOR DISEASES AND COMPETITORS

The mushroom crop is subject to 'diseases' (such as Bubble) caused by fungi or bacteria which
are parasites of the mushroom or of the mushroom mycelium. The mycelium may also have to struggle against 'competitors' or 'weed fungi' (such as the Plaster Moulds) which
reduce the amount of food available and/or produce toxic substances which retard or pre- vent its
growth.

The major diseases and competitors are mentioned in this chapter in alphabetical order, with
brief notes on treatment- which should be supplemented by a study of Chapter 16. [Note: Ch 16
dealt w/ sterilization. Those techniques have been discussed in depth on these boards so far and
the chapter offered no substantial, new information.]

Bacterial Pit: Dark pits on or within the cap. About each pit, which is often coated with slime, is
a shallow, discoloured zone. No certain control is known.

Bacterial Spot (Bacterial Blotch, Brown Blotch) : Areas on the cap turn yellow then chocolate-brown; the discoloration rarely extends more than 2 or 3 mm. below the surface. Bacteria thrive
in conditions of high humidity and inadequate ventilation. Mushrooms should be dried off as
quickly as possible after being watered. Dusting with 'zineb' regularly each week after casing and
between flushes has given some control in the States ; no one knows why or how. Some success
attended Lambert and Ayers's experiments with chlorinated water.

Dactylium dendroides Fries (Cobweb, Mildew, Soft Decay): A fluffy, white, cobweb-like mould
grows over the casing and envelops all mushrooms in its path, causing them to rot. Here and
there it turns pink. Patches of Dactylium should be well covered with 20 per cent PCNB dust,
whether or not they have overrun any mushrooms. Affected mushrooms should be re- moved
with care, and burnt. The disease usually comes in with the casing, but the spores may be
introduced by air currents or flies. Zineb dust is the usual control, but dusting affected areas with
calcium hypochlorite may be more effective. ('Mildew' has nothing in common with the true
mildew diseases of plants.)

Die-back: See Virus diseases.

Diehliomyces micros porus Diehl & Lambert (Truffie, Calves' Brains): formerly known as
Pseudobalsamia microspora) : The term Calves' Brains well describes the round, cream-coloured
fruiting bodies which form in the bed and on top of the casing soil (dangerously resembling fused
pinheads such as are often seen during first flushes). These 'brains' vary in length from a
millimeter to 1.5 in. or more. As they mature they turn reddish- brown, shrivel and release their
spores. Growers who wish to escape Truffie are advised to run their spawn at 60? F ., at which
temperature the spores will not germinate. A temperature of 65? is required by the Truffie spores,
and the presence of mush- room mycelium seems to act as a stimulant. Two difficulties arise
when one attempts to put this advice into practice. First, intensive cultivation calls for quick
growth, and unless the seriousness of a recent attack of Truffie is fresh in one's mind there is a
temptation to risk the higher temperatures more con- ducive to a rapid spawn-run. Secondly,
Truffie seems to be more prevalent in the summer months, and unless the insulation of houses is
well above average it is often impossible to keep bed temperatures below 65?, especially as the
spawn-run itself gener- ates several degrees of heat. Truffie cannot yet be cured, al- though there
are reports of sma1l-scale isolated attacks having been overcome by allowing the beds to dry out
for a month. It is optimistic to expect such a recovery, but if the infection is lim- ited to small,
well-defined areas the trouble may be stopped from spreading by removing soil and compost
entirely from those areas. Great care must be exercised during this operation not to spill any of
the infected compost on floors and paths, whence it could be carried on workers' boots into new
houses, the soil store or the composting shed-with disastrous consequences. Many growers cut
channels across the bed on either side of the infected area as a precaution against spread, and
allow the isolated section to dry out in situ rather than run the risks involved in removing the bed.
They often playa blowlamp over the ex- posed surfaces of the bed-boards in the channels, in case
any Truflle spores remain; the customary fungicides have no effect on the spores, although the
mycelium is less resistant. If the attack is widespread, the wise grower will not waste time with
palliatives; he will empty the house and start afresh. It is com- forting to learn from America that
this deadly form of competi- tion is rarely carried over from one crop to its successor. The
Yaxley Research Station discovered that copper sulphate mixed with the compost at a rate of
0.02-0.1 per cent may prevent the development of Truflle without interfering with the spawn-run,
but commercial trials were generally disappointing.

Fusarium spp. (Damping Off, Wilt) : A form of wilting found on mushroom beds is attributed in
Great Britain to the inhibitory activity of Fusarium species, principally F. martii App. & Wr. and
F. oxysporum Schl. In the early flushes some appar- ently normal mushrooms are found to be
rubbery and the in- terior of the stalks is dry, pithy and brown in colour .Later mushrooms are
small and stunted, and remain indefinitely on the beds in a withered condition; their colour is a
characteristic burnished brown. The trouble is believed to come in with the casing material. Once
a bed is attacked there is no cure, but the trouble may be checked by cutting 9-in.-wide trenches
across the bed several feet in advance of the diseased mushrooms, re- moving the compost down
to the bed-boards and dusting the trenches with hydrated lime. Plenty of fresh air in the house,
the use of a casing soil which permits the beds to 'breathe', and pasteurization of the soil, are all
advised. Fusarium is not recog- nized in the United States as antagonistc to mushrooms, but in
Britain the evidence is difficult to refute. Before the last war, 'damping off' was very prevalent,
and in a great many instances a Fusarium was isolated and identified. The occurrenceof'damp-
ing off' in the presence of a Fusarium was considered too marked to be merely coincidental, and
inoculation experiments success- fully reproduced the symptoms. American workers, on the
other hand, suggest that the conditions of poor ventilation and a heavy crust on the soil often
associated with outbreaks of 'damping off' may themselves be the cause.

La France: See Virus diseases.

Mummy Disease: 'Crook Neck' or 'Wormhole Disease' is a most serious problem with the
industry in the United States, but it was not reported in Europe until 1948. Although long thought
to be caused by virus, it has now been demonstrated to be bacterial in origin. The first symptoms
of the disease are small, tilted caps on long, thin stalks which often lean over slightly. At a later
stage the mushrooms cease to grow after reaching button size, when they turn grey or brown and
become dry, leathery and mummified. If a stalk is broken from the cap, black specks resembling
grub-holes can be seen. There is often a heavy growth of mycelium around the base of the stalk.
Once a bed is at- tacked, the disease spreads rapidly in all directions at the rate of more than 12
in. daily, but the trenching procedure, described under Fusarium, will limit the extent of the
damage. There is at present no cure.

Mycogone perniciosa Magnus (Bubble): When this fungus attacks mushrooms a white, felt-like
mould grows on them and rapidly reduces them to soft, white putrescences exuding brown
bubbles. A swollen stalk and disproportionately small cap indi- cate infection at an early stage in
the development of the mush- room. Diseased mushrooms should be sterilized on the beds with 2
per cent formalin and promptly removed, regardless of their size and the extent of the infection.
Mycogone is a soil- inhabiting fungus, and the casing should be suspected as the source of
infection, but introduction of the spores by other agencies should not be overlooked. Zineb dust
and chlorinated water have been superseded by benomyl.

Papulaspora byssina Hots. (Brown Plaster Mould) : Brown Plaster Mould looks not unlike White
Plaster Mould in its initial stages, appearing on exposed surfaces of the compost or on top of the
casing soil as a white colony resembling a patch of crumbling plaster. But very soon it matures
and turns cinnamon- brown with the formation of powdery granules which can be recognized
under a good hand-lens or, with more certainty, under a low-power microscope. When the attack
is limited it can safely be allowed to mature before casing; it will probably give no further
anxiety if the compost is good. Some growers prefer to spray it, as soon as it has been
recognized, with 2 per cent formalin. Brown Plaster Mould grows strongly in wet compost.

Scopulariopsis fimicola (Cost. & Matr.) Am. & Bathelet (White Plaster Mould, Flour Mould) :
White Plaster Mould is often found in newly laid beds. It closely resembles Brown Plaster Mould
to the naked eye, but as the colonies mature they turn a delicate shade of pink. By that time the
mycelium of the mould will have occupied most of the compost beneath these colonies, but if the
compost has been properly prepared it is quite com- mon for the mushroom mycelium to grow
through and smother it, particularly if the surface is allowed to dry out a little before casing. If the
compost is poor, on the other hand, the occupied areas will tend to expand and mushrooms may
not appear there. Sometimes whole beds are mottled with large splashes of White Plaster Mould,
and then there is little chance of an economic crop of mushrooms, although watering with a
solution of super- phosphate has been suggested by Pointing. It is not known how the mould
enters the house, but the spores are probably intro- duced by pests or air-currents rather than with
the compost, for they are believed not to survive pasteurization. The presence of too much water
in the compost, and under-composting or an anaerobic peak heat, especially where the manure
contains a high proportion of hay, certainly encourage this trouble.

Sporendonema: A white mould which turns pink and clots the soil is known to growers as 'red
Geotrichum' and 'Lipstick Mould'. Classified as a Sporendonema, its exact identity has not been
finally established. It appears to be introduced with the compost, and to be stimulated by
inadequate ventilation and high humidity. Pasteurization of the compost at 131? F. for thirty-six
hours, and of the soil at 144? F. for half an hour, is stated by Sinden to kill it. In a number of
concurrent outbreaks in the summer of 1948, serious reduction of yield was reported by several
growers in different parts of England. Control in America is effected with calcium hypochlorite
dust. It should not be confused with Dactylium.

Verticillium malthousei Ware, and Verticillium psalliotae Treschow (Brown Spot, Fungus Spot,
Dry Bubble) : Infection in the earlier stages of the mushroom's development causes shape- less
(sclerodermoid) malformations similar to those described under Mycogone. Late infection results
in irregular light brown spotting of the cap, the centre of the spots turning grey and sometimes
splitting open. If the mushroom has been attacked on one side of the cap or on the stalk, a
characteristic downward peeling of the stalk is produced, often accompanied by a harelip arrest
of the development of the cap at that point. Verticillium spp. have their natural home in soil. Kill
diseased specimens with 2 per cent formalin the moment they are discovered, and remove. Mix
benomyl in the casing.

Virus diseases (Die-back, La France, Watery Stipe, X-disease and possibly Brown Disease): In
1948 Sinden first investigated a serious disease at the Chester County Farm of the La France
Brothers and labelled it La France Disease. No mushrooms appeared at the first flush, and onlya
few stragglers at the second. New mushrooms continued to appear, but when about half mature
they stopped growing and died, turning soft and slightly brown. The mushrooms had very thin,
long stalks and thin, rounded caps resembling Ink Caps, and dead specimens two days after being
picked became slimy with bacteria and rapidly decomposed. No causal organism was found, but
Sinden sus- pected a virus.

Once described, it or .something very similar was found to be present on a number offarms in
England. The only solution was thought to be to empty the whole farm and to 'rest' the premises
for several months after a thorough 'cook out' of each house with live steam.

In 1961 Last, Hollings and Gandy discovered after a brilliant, sustained investigation that the
English version of La France and X-disease was caused by virus particles. An electron micro-
scope has now been installed at the Glasshouse Crops Research Institute at Littlehampton, and an
ultrasonic vibration technique developed to isolate virus particles from small amounts of mush-
room mycelium.

Five viruses have been found. Mushroom Virus 2 seems to be more damaging than MV 1,
while MV 3, which has only been seen in combination with one or both the others, aggravates the
seriousness of an infection. MV 4 is the most prevalent.

Unfortunately these viruses induce symptoms that vary greatly with environment, and it is rarely
possible by looking at an un- happy flush to diagnose Die-back with certainty, for some of the
symptoms such as rudimentary gills and watery stalks are more often caused by other factors.

Peak-heating at 135? F. for three days is usually sufficient to kill any viruses in compost, but
in some experiments it was not wholly successful. Compost at the end of a crop, 'cooked out' at
150? F. for twenty-four hours has always been free of virus. Some growers cook out their trays
for a second time when they have been emptied, to make doubly sure. Others gas with methyl
bromide.

A new hazard has been found by Schisler & Sinden; viruses can be carried in spores. So
nowadays, when infection is con- firmed, growers pick their mushrooms closed and go over tem-
porarily to more resistant strains of spawn in the hope that the cycle will be broken, rather than
close down completely for a period.

Yellow Moulds: Small colonies of yellow, browny yellow or yellow-green moulds are often
found in the compost towards the end of a crop. When the crop was poor they were usually held
responsible, and were loosely diagnosed by growers as species of Myceliophthora. The most
harmful was thought to be M. sulphurea Goddard, which we called Verdigris. More danger- ous
still is Mat Disease, attributed to M.lutea Cost. and Matr., in which a corky mat forms a seal
between compost and casing. The Yaxley Research Station initiated an investigation into these
yellow moulds when it was suggested they might not be the cause but merely symptomatic of
cultural or other faults. It at once discovered a number of similar yellow moulds in good as well
as poor composts, and the Littlehampton Institute has taken over the problem. In France the
yellow mould giving most trouble is called Confetti. Opinions differ as to whether these moulds
in general are killed at a peak heat of 140? F., and whether in fact they are introduced with the
compost, for they have been known to enter the house at cooldown. It is advised before emptying
to 'cook out' infected houses with steam and to hold the compost temperature at 140? F. for at
least one hour , with formalin injected into the steam line.

Chapter Eighteen

MINOR DISEASES AND COMPETITORS

Apiotrichum: The only reference I have seen to Apiotrichum in mushroom beds is a report by
Borzini of its extensive

occurrence in 1941-2 in Italy as a greyish-green mould which was considered harmful to
mushroom mycelium.

Arthrobotrys: A condition in the mushroom bed which at various times has been attributed to
Cephalothecium, Trichothe- cium and Cephalosporium seems to be becoming more frequent.
The casing is matted together with a white mycelium, the spawn below dies and the compost is
soggy ; no more mushrooms appear. The mould has been tentatively identified as Arthro- botrys
superba or A. cladodes, an eelworm-trapping fungus. It often follows a concentrated attack on the
compost by eelworms, and it is the eelworms which do the damage-not the mould.

Botrytis sp. ( or Phymatotrichum sp. ; Brown Mould) : A cinnamon-brown mould which spreads
over the compost be- fore casing, or over the casing before mushrooms appear, in characteristic
little blobs. It is not known definitely whether it reduces yields, but it can certainly retard the first
'break' and the general opinion is that, in severe cases, it can diminish crops by the excretion of
toxins. Dust with calcium hypochlorite.

Cephalosporium costantinii: Reported by Smith to be para- sitic on mushrooms, following
isolation from mushrooms which were deformed rather as if they had been infected at an early
stage with Mycogone or Vertici//ium, except that they were dry and rubbery and the surface was
light to dark brown and slightly hairy .

Cephalosporium lamellaecola (Gill Mildew): Smith described this disease as one in which the
mushroom develops normally but the gills are fused together and mottled; that was in 1924. In
1957 Gandy found mushrooms which had dark brown spots and blotches on the caps suggestive
of Verticillium, but the fungus was identified as Cephalosporium lamellaecola. At a later stage in
the disease the mould spread to the gills, which were stuck together as Smith had described.
Bulloch has agreed that this disease was identical with a pathogen he had recorded a dozen years
earlier. It is thought to be quite rare.

Chaetomium olivaceum: A mould occasionally found in the compost before casing. Its fruiting
bodies are noticeable on straw as small, round, olive-green spots. It often appears when beds
have been pasteurized at over 145 F. and then it grows very vigorously at the expense of the
spawn. It has been known to spread into sterilized soil and on to wooden shelving, and when
established, may retard or prevent cropping. Increased ventilation is advised during peak heat.

Chaetomium sp. (White Chaetomium) : A luxuriant mould first with a green tinge but soon
snow-white spreading over the sur- face of the compost before casing; about a month later dark
green fruiting bodies covered with long, spiral hairs may develop below the overlaying white
mycelium. It does not give much trouble so long as the compost is not so poor that the spawn
cannot establish itself.

Clitocybe: Clitocybe dealbata has been known to ruin mush- room crops, but it is not much heard
of to-day. It is a tiny toad- stool which forms groups on the bed up to 3 ft.long. The irregu- lar,
wavy edges of the white, satiny caps turn upwards and the white gills change to pale fawn at
maturity. It is probably intro- duced with the casing soil in the first instance.

Clitopilus: Seen now and then on cased beds, is a beautiful, delicate, white growth resembling
tiny cat's ears on extremely short stalks. The average size when mature is between! in. and 1 in.
in diameter. Its technical name is Clitopilus cretatus, but formerly was referred to as Pleurotus
passeckerianus; growers call it simply Cat's Ear Fungus. It does comparatively little harm, but
removal is recommended.

Coprinus: Fragile toadstools with long, slender stalks and small, thin caps very often appear
either on the compost heap, or on the beds before casing, or on the soil after casing. They
develop rapidly, and as rapidly decay into a black liquid. These are Ink Caps-Coprinus
atramentarius-and their presence is said to be due to under-composting. No grower minds seeing
them in moderation, however; experience suggests there is nothing much wrong with the
compost if they turn up.

Corticium centrifugum: A tentative name for a flat white mould on compost and casing which
resembles the Plaster Moulds but is usually soon overrun in a good compost by the mushroom
mycelium and does not change colour .A few growers believe it can seriously reduce yields.

Didymocladium ternatum Sacc. : A new mildew disease re- ported by Sinden and Hauser in
1953. It differs from Dactylium in that the mycelium stays white, the spores accumulate in little
snowball-like masses, and the mushrooms decay with only little brownish discoloration. The
disease has been devastating on one or two American plants, but has not yet been diagnosed in
Britain. It should be combated in the same way as Dactylium.

Drop Disease: Continental growers report a Drop Disease which they find widespread and very
infectious, but there is no published account of it in Great Britain which has come the way of the
present writer. Affected mushrooms become coated with a sticky fluid and are watery inside. The
cause is probably bacterial.

Mycogone rosea: A rare disease is that caused by Mycogone rosea. Areas on the surface of the
cap turn dark brown and the tissue immediately beneath the brown is bright yellow. Some- times
the affected areas are slightly sunken. The casing is almost certainly the source of infection,
although spores may be intro- duced after 'peak heat' by the usual agencies. Prevention and
control are identical with those prescribed for Mycogone perni- ciosa.

Oedocephalum fimetarium: Not common, though it has been found in this country several times
recently, growing on top of the compost just prior to casing. The soil is sometimes matted
together by the mould, but major injury to crops is improbable.

Panaeolus: A leggy toadstool closely resembling an Ink Cap except for the brown colour ofits cap
is a Panaeolus. Its presence suggests under-composting or excessive watering of the compost.
These fungi compete for the available food, and should be brushed off the bed. They are not
serious enemies.

Penicillium: This bluish-green mould is not believed to attack growing mushrooms except
perhaps when the removal of old 'roots' and dead buttons from the bed has been neglected. It may
then grow round the bases of the stalks of developing mush- rooms. Very wet and acid soils are
said to favour Penicillium species. See also Trichoderma.

Peziza vesiculosa: Small, dull-yellow or buff-coloured fleshy 'cups' sometimes appear on the
beds. They are commonly found on decaying straw. They indicate that the manure has not been
adequately composted, or that too much water has been added during composting.

Phymatotrichum: See Botrytis. Ramularia: See Cephalosporium lamellaecola. Sepedonium sp. A
whitish mould producing yellow-green spore colonies in poorly made compost. Yield does not
seem to be affected except in extreme cases but this mould is said to serve as food for mites.
When the spores germinate, according to Kneebone, they produce abundant conidia and large
yellow chlamydospores.

Spicaria sp. (Vern Astley Disease): Only one outbreak in Canada and another in the United States
have so far been re- ported of this mould infection of the compost resulting in the distortion of
the mushroom, accompanied by asthma-like con- gestion and coughing among workers emptying
the houses. Sinden reports that in the early stages the mushrooms appear only in patches, with a
tendency for the caps to be scaly. Later the mushrooms exhibit the characteristic flattened cap,
which is small compared with the stalk, and it opens early with a rudi- mentary veil and
discoloured gills. The stalk is spongy at the base, and discoloured higher up.

Sporotrichum sp. : A white mould which produces yellowish conidia in a poor compost,
especially in a synthetic compost containing corn-cobs. Yield is not thought to be affected except
in severe infections, but it too is believed to attract mites.

Stysanus stemonitis (Black Whisker Mould) : A grey-to-black mould appearing on and in the
compost. It is not yet certain whether it affects crops, but the copious production of spores has
caused serious breathing difficulties among workers empty- ing the house.

Trichoderma spp. are frequently found on beds where formalin has been employed to kill other
unwanted moulds.

Trichoderma koningi Oudem. : This parasitic Trichoderma Mildew was also first reported by
Sinden and Hauser in 1953. The enveloping mould remains greyish, the sage-green spores not
being readily visible. It develops from dead tissue (if left on the beds) and overwhelms anything
in its path, turning the caps of mushrooms brown, but the discoloured areas are not sunken as
they are with Trichoderma Spot. Use zineb. Kill early infec- tion with calcium hypochlorite
powder applied to localized patches.

Trichoderma viride Persoon or T. lignorum (Tode) Harz: Trichoderma Spot or Blotch is not to be
confused with the preceding disease. It is a green mould acting similarly to Penicil- lium, and is
associated with decaying organic matter in the casing. According to Sinden and Hauser, it
'develops toxic substances which are absorbed by the growing mushroom, resulting in dry,
brownish lesions starting on one side of the stem and extending into the cap'. This phenomenon
is readily differentiated from symptoms of Verticillium by the microscope. Treat as for
Trichoderma koningi.

Xylaria: Blackish, fleshy, irregular strands resembling small roots and measuring up to 6 in. in
length sometimes appear in the compost and casing soil, and have been known to send up pinkish
branches. This 'Mushroom-bed Sclerotium' is Xylaria vaporaria and lives in soil, so that if such
soil be intended for casing it should first be sterilized. Careful removal of these 'roots' as soon as
they are discovered may save the bed.

*Species of Haplotrichum and Corethropsis have been found by Williams in samples of casing
soil, binding it together. Neither is regarded as likely to become a serious competitor .