Front Cover

Group Title: Bulletin New Series
Title: Mushroom growing
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00003062/00001
 Material Information
Title: Mushroom growing
Series Title: Bulletin New Series
Physical Description: 24 p. : ; 23 cm.
Language: English
Creator: Florida -- Dept. of Agriculture
Publisher: State of Florrida, Dept. of Agriculture
Place of Publication: Tallahassee Fla
Publication Date: 1934
Subject: Mushroom culture -- Florida   ( lcsh )
Mushrooms -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
General Note: "August, 1934."
General Note: Cover title.
 Record Information
Bibliographic ID: UF00003062
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA3564
ltuf - AKD9452
oclc - 28539597
alephbibnum - 001962775
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Table of Contents
    Front Cover
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Full Text

New Series




August, 1934

Fr _______~'~n~d~C~tr~fiE

No. 49


Mushroom Growing

The mushroom is a rapidly growing fungus of the class
"Basidiomycetes" and order "Agricales." There are
edible, non-edible, unpalatable and poisonous varieties.
Millions of pounds of edible mushrooms are consumed in
this country annually and a large per cent of them are im-
ported from Europe.
The edible mushroom is classified botanically as
"Agricus campestris" or "Psalliota campestris." More
than a thousand species of mushrooms are known, but the
common cultivated variety above mentioned is the only
species cultivated in the United States, and most of the
mushrooms consumed are of this type. In European and
Oriental markets several other kinds of fleshy fungi are
sold. The Cepes and Truffles of Europe, the Kames of
North Africa and the Shii-take and the Mastsii-take of
the Orient are examples.
The use of the word "toad stool" as applying to
all poisonous mushrooms is erroneous. The fact is there
is no line of demarkation that holds good when applied
to all varieties of this group of fungi. The list of edibles
allowed on the markets of some countries is not the same
as the list allowed in other countries. The varieties are
of different sizes from the almost microscopic to the large
puff. They differ also in texture and quality covering
such a variety as gelatinous, fleshy, cartilaginous,
leathery, corky and woody.
The following is from the Encyclopedia Brittanica:
"The parts of a mushroom consist chiefly of stem and
cap; the stem has a clothy ring round its middle, and the
cap is furnished underneath with numerous radiating
colored plates (lamellae) called gills, free from the stem.
The cap is fleshy, firm and white within, never thin and
watery: externally it is pale brown, dry, often slightly
silky or floccose, never vacid.
"The cuticle of the mushroom readily peels away from
the thick flesh beneath. The cap has a narrow dependent
margin or frill; this originates in the rupture of a deli-
cate wrapper, which in the infancy of the mushroom
entirely wraps the young plant. The gills under the cap
are at first white, then rose-colored, finally brown-black.
A point of great importance is to be noted in the attach-
ment of the gills near the stem; the gills in the true mush-
rooms are. however, more or less free from the stem, they

never run against it or down it. When a mushroom is
perfectly ripe and the gills are brown-black, they throw
down a thick dusty deposit of fine brown-black or purple-
black spores: it is essential to note the color. The stem
is firm. slightly pithy up the middle, but never hollow; it
bears a floccose ring near the middle; this originates by
the rupture of the thin general wrapper of the infant

The following is taken from circular 251, December,
1932. of the United States Department of Agriculture:

Circular No. 251--1932--U. S. Department of Agriculture
The practice of cultivating the common mushroom orig-
inated in France in the latter part of the seventeenth
century. but it was not until toward the end of the nine-
teenth century that it began to gain a foothold in the
United States. At first mushrooms were grown as a side
line to market gardening, but as the market developed
specialization began.
Although at first abandoned limestone quarries, mines,
and sandstone caves were used. the structure that event-
ually found most favor in this country was the specially
constructed mushroom house filled with tiers of shelf
beds. On the average. better crops are obtained in these
houses than in caves, because favorable conditions can be
more readily obtained and diseases and insect pests are
more easily controlled.
As a result of the widespread use of these special
houses and the development of better methods of making
spawn, the industry has made rapid strides in the last 30
years and at present 15.000.000 to 20,000.000 pounds of
mushrooms are produced annually. About three-fourths
of the industry is located in eastern Pennsylvania and
northern Delaware. near the ready markets for mush-
rooms and supplies of manure in New York City and Phil-
adelphia, but there are also important centers in other
Since the beginning of mushroom culture growers have
planted their beds with a specially prepared material
filled with living mushroom mycelium called spawn. In
the early days of mushroom growing the spawn was made

from mycelium found growing naturally in the fields or
in the caked horse manure of the mill tracks. The spawn
maker planted this mycelium in special beds which were
later broken up and sold to the growers. This type of
spawn was called French-flake spawn. The original wild
mycelium used to inoculate these beds was called virgin
spawn or mill-track spawn. Spawn made according to
this method was loose and easily injured by excessive
heat and drying out. An improvement devised in England
early in the nineteenth century consisted of allowing the
mycelium from the bits of virgin or mill-track spawn to
grow into compressed bricks made of a mixture of horse
manure, cow manure, and partly rotted leaves. This
product, known as English brick spawn, was superior to
French-flake spawn in keeping and shipping qualities.
But with both types of spawn it was difficult to maintain
pure varieties, and often fungus diseases and insect pests
were distributed with the spawn.
Spawn was first made from pure cultures in France
shortly before 1900 and in the United States a few years
later. In France spawn was grown from germinated
spores while in the United States the mycelium was ob-
tained by the simpler tissue-culture method, which con-
sisted of sowing in bottles of sterile manure bits of mush-
room tissue extracted under aseptic conditions from the
caps of young mushrooms. After the original spawn was
obtained in pure culture by these methods it was used in
the place of the virgin spawn to inoculate the bricks.
These methods enabled the spawn maker to sell spawn
of known varieties and to start cultures comparatively
free from disease. But the spawn sold to the grower was
not a pure culture and there was still an opportunity for
diseases and insect pests to accumulate during the incu-
bation of the bricks and to be distributed with the bricks.
About 14 years ago the most successful spawn makers
in the United States abandoned the tissue-culture method
for the spore-culture method and a few years later began
selling, direct to mushroom growers, quart bottles of pure-
culture spawn of the type formerly used to inoculate
bricks. Spawn of this kind has the obvious advantage
over the old brick spawn of being free from harmful
fungi and insects. At the present time nearly all the
spawn used in the United States is bottle spawn grown
from germinated spores. It gives the grower a practical
approximation of pure-culture spawn, pedigreed and free
from diseases and insect pests, the only disadvantage be-
ing the comparatively poor keeping quality.

The methods used in manufacturing bottle spawn are
adaptations of ordinary pure-culture laboratory technic
to large-scale production. The principal operations are
the collection of spores, the germination of spores, and
the preparation, transferring, and incubation of spawn
In order to obtain pure cultures, mushroom spores are
collected and grown under aseptic conditions. Methods
of obtaining a pure collection of spores are based on the
fact that the young gills of disease-free mushrooms
develop under approximately aseptic conditions in filtered
air before the veil is broken, and the mushroom will con-
tinue to expand and produce spores even after it has been
surface sterilized, peeled, or cut up. Different procedures
may be followed to prevent spores of molds on the sur-
face of the mushroom from contaminating the cultures.
Stems may be removed and the surface layer peeled off
with sterile forceps; the mushroom may be surface
sterilized by flaming it or soaking it in a disinfectant;
or the spores may be transferred directly from the gills,
or from spore "prints" made by suspending the treated
mushroom over a sterile surface in a sterile container.
The spores are transferred for germination either
directly to sterile washed compost or first to agar media
to make certain that the culture is free from contaminat-
ing molds and bacteria. Ordinary potato-dextrose agar
and beer-wort agar are suitable media. If the culture is
pure it will be at least four days to two weeks before any
growth appears even at a favorable temperature. 75 F.
When agar is used the mycelium is usually allowed to
make a good growth on the agar before it is transferred
to spawn bottles.
The material most generally used for filling spawn
bottles is manure, short in straw and composted longer
than for use in beds. screened and partly dried. This
material is tamped firmly into imperial-quart milk bottles
and a hole is bored through the center for ventilation.
The bottles are then plugged with cotton and steam
sterilized. At a temperature of 70 to 80 F. the myce-
lium usually runs through the sterile manure in about 30
days. The spawn from these bottles is used to inoculate
compost in other bottles similarly prepared. As a rule,
repeated transferring is limited to three generations from
the original cultures to avoid so-called running out and
the danger of accumulating contamination. Bottles

newly "run" with mycelium are suitable for immediate
use in planting beds. If not used immediately they are
usually kept in cold storage.
The following special equipment is necessary for suc-
cessful spawn making: A microscope to discover the
nature of contaminating molds; a small autoclave for
the preliminary culture work; one or more large canners'
retorts for sterilization; and apparatus for measuring the
reaction of media and manure. In addition, most spawn
makers use laundry centrifuges to dry their manure and
special motor-driven cutters to shred it. This apparatus
and machinery must be housed, special inoculating and
incubating rooms are necessary, and cold-storage facili-
ties must be provided for storing spawn. The establish-
ments of the leading spawn makers represent a total capi-
tal investment of from $20,000 to $50,000. Because of
this only a few growers in the United States have special-
ized in making spawn. These few, however, make a high
grade of pure-culture spawn originating from germinated
spores and, because of large-scale production and com-
petition, are able to sell spawn cheaper than the average
grower could produce it at home.
A list of established spawn makers will be furnished on
request by the Division of Mycology and Disease Survey,
Bureau of Plant Industry. United States Department of
Agriculture, Washington, D. C.

Several distinct varieties of the common mushroom are
cultivated, but for convenience the trade has grouped
them according to the color of the cap, as white, brown,
and cream. The terms white and brown refer to distinct
varieties, but there are several cream varieties. The
white variety usually commands the highest price on the
market, owing to its color. It is prolific but is far from
ideal because of its tendency to stain when bruised by
handling and to produce clusters on the beds and an
excess of button mushrooms. The brown variety is dis-
criminated against in most markets, but has advantages
over the white in better shipping quality, firmer flesh, and
production of fewer button mushrooms. Cream mush-
rooms are intermediate in color and combine the other
characteristics of the white and the brown in different
degrees, depending on the variety.
It has been customary to consider all cultivated mush-
rooms as varieties of "Agaricus campestris." However,

there are undoubtedly heritable differences in the color,
form, and growth habits of these so-called varieties which
breed true from spores, and in all probability some of
them will be considered distinct species when given crit-
ical taxonomic consideration.

Mushrooms can be grown in any structure in which the
grower can control ventilation, maintain a moderately
high humidity, and a range of temperatures between 550
and 65 F. Contrary to popular belief, sunlight is not
harmful to mushrooms, and they are usually grown in
windowless sheds and in caves simply because it is easier
and cheaper to control temperature and humidity in
structures without windows. Old barns are frequently
used. Occasionally waste space in greenhouses is planted
to mushrooms. A successful grower near Chicago has
been growing mushrooms in an old brewery for more than
a decade. Sandstone caves along the Mississippi River
near St. Paul. Minn.. have been used by commercial mush-
room growers for more than 40 years. Along the Hudson
River near Albany, N. Y., mushrooms are grown exten-
sively in the old ice houses. Near Pittsburgh. Pa., they
are grown in partly abandoned mines, and near Akron,
N. Y.. abandoned limestone quarries have been used for
30 years.
In the industry as a whole, however, the specially con-
structed house has found most favor, and at least three-
fourths of the mushroom crop in the United States is
grown in these houses. The principal advantages of the
special mushroom house are: It can be suitably located
with relation to railroad facilities, markets, and manure
supply; ventilation, temperature, and humidity can be
easily controlled, the air temperature in the house being
raised during final fermentation and the moisture and
temperature controlled during the spawn run and the
bearing period; separate houses may be handled as units
during fumigation, and prevent the migration of harmful
fungi and insects from old beds to new. The disadvan-
tages are the high initial cost of the house and the high
cost of cooling it for the summer crop.
The principal advantages in using caves or mines for
growing mushrooms are: The small initial investment,
the low temperatures for growing mushrooms in the sum-
mer, and the uniform temperature during the growing
period. The disadvantages are: The difficulty of disin-

fecting and ventilating, often a limiting factor in produc-
tion in these structures; the fact that the temperature
around the beds is not raised during the final fermenta-
tion; dripping and excessive humidity in summer; the fact
that bed temperatures can not be controlled during the
spawn run and that distances from railroad facilities,
markets, and manure supply are frequently great.


Commercial mushroom houses are designed to simplify
and facilitate such operations as filling the beds, spawn-
ing, picking, emptying the beds, disinfecting, fermenta-
tion in the house, heating soil, heating, and ventilating.
Experience has shown that a house constructed along
these general lines meets these requirements.


In a standard house there are two tiers of beds, 5 to 10
beds high. A space of 6 inches to 1 foot is left beneath
the bottom bed to insure a good "heat" during the fer-
mentation of the compost in the bed. A space of 2 feet
is allowed between the bottom boards of the beds. These
bottom boards are laid in loose in order to facilitate fill-
ing and emptying the beds. The side boards are also
loose and are held in place by the compost in the bed.
The beds are usually 6 to 8 inches deep and 6 feet wide-
sometimes 5 feet-and run the full length of the house,
with the exception of the alleys at the ends of the house.
The tiers of beds are supported by 2 by 4 inch uprights
set at 4-foot intervals. The uprights are joined beneath
the bottom boards by 1 /2 by 6 inch bed supports.


A space about 30 inches wide is usually provided be-
tween the tiers of beds to form a service alleyway which
runs the full length of the house. This alley is used in
filling and emptying the beds. An elevated runway is
built in this alley to make it easier to fill the upper beds.
Often the house is built lengthwise into a sidehill with the
high ground at the level of the elevated runway. An
18-inch alleyway between the outside walls and the tiers
of beds is also provided to facilitate picking.

The length of the house is usually determined as the
result of a compromise between the ideas of a long house
economical to build and a short house convenient and
economical to fill. Many successful growers consider 65
feet a suitable length. If the house is constructed with
two tiers of beds (six beds high, including the floor bed),
the width of the house is about 20 feet. Obviously the
height depends on the number of beds in a tier; usually
3 feet is allowed for working space between the top beds
and the ceiling. Often several houses are joined together
and built alongside each other. When this is done it is
customary to make one roof cover four tiers of beds. Two
houses joined under one roof in this way are called a
double house.

There are six doors in a mushroom house-three at
each end.

Mushroom houses must have ventilation systems which
provide gradual changes of air with the least possible
direct draft over the beds. Ventilation usually is accom-
plished by occasionally partly opening the doors and
opening the hinged vents in the ceiling. To facilitate air
circulation the ceiling is sloped upward from the side
walls to the ventilators over the center aisle and likewise
from one end of the house to the other. In some houses
provision is made for drawing the air off the floor and dis-
charging it outside, and the ventilators may be screened
to prevent the entrance of mushroom flies.

Several growers have installed small refrigeration
plants to assist them over warm spells in the late spring
and early fall and a few have cooling plants extensive
enough to enable them to grow mushrooms in the summer.
The small refrigeration plants are usually based on the
washed-air principle and water pumped from deep wells
is used as the cooling agent. The larger plants use
mechanical refrigeration, in some cases supplemented
with water sprays. In either case the house must be well

insulated and the plant must be so designed that it can
be cooled without excessive humidity or circulation of air.

Mushroom growers usually use hot-water heat. The
radiation generally consists of four or five pipes running
around the house, hung on the inside of the walls, within
a few feet of the floor. In view of the recently adopted
practice of supplying auxiliary heat at the time of the
final fermentation, provision should be made for the occa-
sional use of steam.
The walls are made of any material having fair insu-
lating value, which will withstand dampness. Many
growers make their walls with a single layer of siding.
Others use a double wall filled with cork. Some use
cinder blocks, tile, etc. When the house is built with a
ceiling it is the general practice to cover the floor of the
loft with about 5 inches of loose shavings, for heat insula-
tion. The bottom boards and sideboards of the beds are
usually made of cypress, which resists rotting.

The average mushroom house, 65 by 20 feet, with beds
arranged in two tiers six beds high, contains 4,320 square
feet of bed space. Since it takes 1 ton of manure to fill
70 square feet of beds, such a house requires approxi-
mately 60 tons of manure. It is essential that the manure
capacity or bed space be large as compared to the air
space, for three reasons; namely, a large proportion of
manure to air space insures a better heat during the fer-
mentation in the house; a large capacity makes it easier
to maintain a high relative humidity; and it cuts down the
capital investment per square foot of bed space.

Although there is necessarily considerable difference in
the details of the procedure followed by growers under
different circumstances, the primary objectives are virtu-
ally the same for all. They are the preparation of a suit-
able compost, the establishment of favorable conditions
for growth and reproduction, and the control of fungus
and insect pests by routine sanitation and disinfection.



The temperature at which the house is held largely
determines the length of the growing period and has con-
siderable influence on the quality of the mushrooms. If
the temperature is kept between 45 and 55 F. good beds
continue to bear mushrooms for five or six months,
whereas in a house held at 60 to 65 the beds exhaust
themselves in three months. In the former case, as a
rule, the mushrooms grow somewhat larger and are dis-
tinctly firmer and heavier than those grown at the higher
temperatures. The total yield is approximately the same
with perhaps a slight advantage in favor of the beds held
within the low temperature range. When two or more
crops are grown in one season, time is an important con-
sideration and the beds must be kept above 55 The
practice of maintaining a uniform growing temperature
is widely favored, although many growers prefer to start
their crops at a low temperature and bring on successive
growths of mushrooms at slightly higher temperatures.
The temperature limits at which the common cultivated
varieties of mushrooms can be grown are 45 to 68 .
Lower temperatures delay the crop but do not perma-
nently injure the beds. On the other hand, during the
time when the mushrooms are on the beds a period of
more than a few days with a temperature in the house
over 70 will often injure the crop seriously.

The relative humidity in the average mushroom house
during the bearing period ranges from 70 to 80 per cent.
This condition is easier to maintain in some houses than in
others because of the difference in the exchange of air
through cracks and crevices and differences in the propor-
tion of air space to bed space. When the humidity is
allowed to drop much below 70 per cent the casing soil
has a tendency to dry out too quickly and the surface of
the mushrooms becomes tough and under extreme con-
ditions cracked and seamed. Conversely. if too high a
relative humidity is maintained, the mushroom disease
known as "spot" will be aggravated by the reduced rate
of evaporation of the contaminated water spattered on
the mushrooms during the watering of the beds.

Procedure in watering mushroom beds is governed
largely by two objectives: Maintaining in the soil the
proper moisture content to induce therein an abundant
growth of healthy mushroom strands or rhizomorphs;
and minimizing the number of spots and blemishes on the
surface of the mushrooms caused by water spattered on
growing mushroom caps. Usually water is first applied
to the beds shortly after they are cased. At this time the
beds are watered lightly every day until there is just
sufficient moisture in the soil to cause normal strand for-
mation throughout the soil layer. This moderate moisture
content is maintained until the mushrooms begin to
appear. Care should be taken to avoid an excess of
water in the soil at this time, as it may prevent normal
strand formation and seriously reduce the subsequent
yield of mushrooms. The amount of water necessary to
maintain the proper moisture content is quite different for
different soils and in different localities and seasons. It
depends on the relative humidity in the house, the mois-
ture content of the compost, and the water-holding
capacity of the soil. In general, several light waterings
are preferable to a few heavy ones because of the danger
of excess water percolating through the soil and causing
the formation of a wet layer of manure under the soil.
Such a layer may prevent the healthy mushroom myce-
lium lower in the bed from growing up to the soil.
Puddles of water on the bed are also objectionable be-
cause they tend to stimulate the development in the soil
of a harmful green mold and to cause submerged pinhead
mushrooms to turn brown and die. On the other hand, if
the soil is too dry or if only the upper layer is moist, fewer
mushrooms will develop, and the first mushrooms to come
up will have a tendency to form beneath the soil layer
rather than on the upper surface.
After the mushrooms begin to appear they usually
develop in sudden outbreaks at intervals of about a week.
These outbreaks are called "flushes" or "breaks" and are
followed by periods during which there are only a few
mushrooms on the beds. There are several systems of
watering in relation to these breaks. Some growers water
only between breaks so as to avoid wetting the mush-
rooms. Others water lightly two or three times a week
regardless of the breaks. Many follow a compromise
system of watering regardless of the breaks during the
first three breaks. During this period spotting is not

serious because the fresh mycelium is vigorous and harm-
ful fungi and bacteria in the soil are comparatively
scarce. Thereafter, watering is done only between
breaks. In any case, when water is applied to the beds
while mushrooms are growing a gentle shower is used to
avoid spattering soil on to the caps of the mushrooms, and
ventilation is increased after watering until the droplets
on the mushroom caps are evaporated.
Considerable ventilation is necessary in growing a good
crop of mushrooms, and it is advisable to give as much
ventilation as possible without interfering with tempera-
ture and humidity control or causing excessive evapora-
tion from the beds by cross drafts. Usually it is easier
to ventilate, without interfering with these factors, in
the spring and fall months. When the temperature out-
side the mushroom house is higher than that inside, the
fresh air will become damp upon entering the house.
Conversely. cold air brought into a warm mushroom house
absorbs moisture and will have a tendency to lower the
relative humidity inside the house.

As congested centers of mushroom growing develop it
is becoming more and more apparent that cumulative
losses caused by fungi and insect pests can scarcely be
avoided unless a carefully planned program of disinfec-
tion and sanitation is made a part of the routine of cul-
tural practice. It is advisable to thoroughly disinfect the
composting grounds and the mushroom house between
crops and to take special precautions to prevent the con-
tamination of casing soil and water.
A few growers have concrete composting surfaces, but
in most cases the manure is composted on the bare ground
and a sanitary condition is maintained by keeping the
ground free from old manure and standing water between
crops and by thoroughly drenching the soil with a disin-
fectant a few weeks before assembling the manure. A
solution of formaldehyde made by dissolving 1 pint of
fresh formalin in 15 gallons of water has satisfactory
germicidal properties for this purpose and in addition has
the advantage of being non-corrosive to metals and of
remaining only temporarily in the soil.

It is almost a universal practice to thoroughly disinfect
the inside of the mushroom house a few weeks before fill-
ing time either by burning sulphur or releasing formal-
dehyde gas. Effective fumigation may be obtained by
either method, especially under warm, damp conditions,
but both sulphur fumes and formaldehyde gas are in-
jurious to growing mushrooms and special precautions
are necessary when fumigating a house adjacent to one
in which a crop is growing.
When sulphur is used it is usually burned at the rate
of 5 pounds per 1,000 cubic feet of air space. Either
crude sulphur or flowers of sulphur will burn readily with
the aid of rag wicks soaked in kerosene. Deep containers
must be used and air pockets in the sulphur heap must be
avoided in order to minimize the fire hazard of running
molten sulphur and burning sulphur spattering over the
bed boards. It is not advisable to burn sulphur directly
on the cement floor of the alley, since the heat generated
may cause the cement to buckle and throw out particles
of burning sulphur. Some growers burn the sulphur out-
side the house and use a forced draft to blow the fumes
into the house.
Fumigation with formaldehyde is accomplished by
vaporizing commercial formalin-40 per cent formalde-
hyde solution in water-at the rate of 1 quart to 1,000
cubic feet of air space. The formalin is usually placed in
pails or tubs along the alley and vaporized by adding
crystals of potassium permanganate at the rate of 1 pound
per quart of formalin. As in fumigating with sulphur, all
preparations for quickly leaving and closing the house
should be made before the gas is released and exposed
lights should not be used in the house, since formalde-
hyde gas is explosive under certain conditions.
While the crop is being picked all mushrooms affected
with bubbles should be carefully removed from the house
and burned to prevent the spread of the disease. After
doing this work the men should thoroughly disinfect their
hands. It is also advisable to burn all mushroom refuse.
After each crop all traces of spent manure should be re-
moved and disposed of so that none will be used on fields
near the mushroom house or where it can possibly con-
taminate prospective casing soil.
The water supply also should be carefully guarded
against contamination with fungus spores or any traces
of grease or oil which might cause diseased or deformed

For general disinfecting around the packing house, or
disinfecting workmen's hands or diseased areas on a bed,
commercial preparations having carbolic acid, creosote,
hypochlorite. or mercury as active ingredients are widely
There as three general classes of mushroom diseases:
Those caused by parasitic fungi or bacteria; those caused
by fungi which make conditions unfavorable for the
mushroom by growing like weeds in the bed; and those
that cause malformation of the mushroom apparently
stimulated by nonliving irritants. The bubbles and spot
are examples of the parasitic class, plaster mold and
truffles are examples of the weed type, and rose comb is
an example of the irritant type. Certain of the more
important of these are described on the following pages.

Bubbles is the most destructive disease of cultivated
mushrooms. It is caused by the fungus "Mycogone
perniciosa" Magn., which grows into the mushroom and
transforms it into a distorted, putrid mass. Soon after
the mushroom is attacked the parasite produces a layer
of white or brown spores over the surface. These spores
may be spread by various agencies and are able to live
through a long rest period under unfavorable conditions.
The recurrence or accumulation of the disease from one
crop to another indicates that the fungus either is remain-
ing alive inside the house from one crop to another or is
being carried into the house during one of the cultural
operations. There are several possible methods of intro-
ducing the fungus into the house-in the air or on insects
entering through doors or ventilators, or in the water,
spawn, compost, or soil. or on the clothing or hands of
If the house is thoroughly disinfected with either sul-
phur or formaldehyde there is practically no chance for
inoculum to remain in the house from one crop to another.
Likewise. disinfection of the area surrounding the house
and sanitary disposal of mushroom refuse will materially
reduce the danger from wind-blown or insect-carried
spores. If an open well is used it may be necessary to
disinfect it occasionally. There is little chace for Myco-
gone to be spread in bottle spawn that has been made
under aseptic conditions.

Mycogone is killed by long exposure to moderately
high temperatures. All the evidence at hand indicates
that a temperature of 1200 F. for 48 hours in a mush-
room house will eradicate the fungus from the house, and
the manure in a house which has been through a good
heat should be free from Mycogone. This and other cir-
cumstantial evidence indicates that most severe outbreaks
of bubbles in commercial houses are due to carelessness
in disinfecting the house or to infested casing soil.
Losses from infested casing soil can be eliminated by
taking precautions to prevent the contamination of the
soil. To determine whether soil is contaminated, small
test beds may be cased with soil samples taken from
fields that are to be used as sources of soil for subsequent
crops. If soil infestation becomes general and there is no
Mycogone-free soil available, the fungus can be eradi-
cated by heating the soil to at least 1200 F. for 48 hours.
This can be done in specially equipped rooms, or by plac-
ing the soil in trays near the top of the house during the
heat, if the heating plant is large enough to raise the
temperature artificially in the event that the manure does
not generate sufficient heat. When the soil is heated to
more than 1500, Mycogone spores are killed in less than
an hour. Some growers find partial sterilization with live
steam, as described in Farmers' Bulletin 1629, quite satis-
factory. Others complain of a loss of water-holding
capacity and molding of the steamed soil. The injurious
effect of steaming apparently varies with different types
of soil and in many cases is temporary and can be elimi-
nated by steaming some time prior to casing, or by aera-
tion of the steamed soil.
After the disease has become established in a house
strict sanitary measures are necessary to prevent work-
men from spreading it. The loss may be reduced some-
what by growing the crop around 50.
The measures outlined above apply particularly to the
prevention of the disease in conventional mushroom
houses, but the principles may be applied to most situa-

The spot disease of mushrooms caused by "Bacterium
tolaasi" (Paine) Elliott and other soil organisms is found
wherever mushrooms are grown commercially. It is the
most troublesome disease in caves and is often quite
serious in standard houses, especially toward the end of a

crop period or in growing summer crops in artificially
cooled houses. It is characterized by brown, almost
black, spots over the surface of the mushroom cap. These
spots are often covered with a bacterial ooze. Usually
they do not penetrate deeply into the mushroom flesh,
but at times the bacteria follow along the tunnels of fly
larvae and blacken the entire stem and parts of the cap.
Infection is known to be favored by high humidity and
prolonged wetting of the mushroom caps while watering
the beds. Circumstantial evidence indicates that the
inoculum comes principally from the soil. Growers should
endeavor to avoid spattering water from the soil on to the
mushrooms, take every precaution to prevent the house
from becoming too damp, and, weather permitting, at-
tempt to dry off the mushrooms rapidly after watering by
opening the doors and ventilators for a few minutes.
Mushrooms on old beds seem to be more subject to spot-
ting than do new breaks and at times poor ventilation
seems to be an aggravating factor.

The "green mold" disease spreads in patches from the
masses of mushroom tissue which are sometimes left in
the soil after picking. Once a patch of the fungus caus-
ing this disease becomes established in the soil, more
button mushrooms are rarely formed in that area. Its
development can be retarded by removing all of the solid
fungus tissue at the base of the mushrooms when pick-
ing them, and filling the holes with fresh soil. Excessive
dampness should also be avoided. Liming seems to be
somewhat beneficial as a preventive but not as a control
The presence on the bed of a large proportion of de-
formed mushrooms with superfluous gills over the upper
surface of the cap resembling the rose comb of poultry
and sometimes deeply seamed and cracked has been
traced in many cases to mineral oil or oil products. In
some cases abnormalities were apparently due to the use
of kerosene in smudges, disinfectants, and insect sprays.
In others they were due to accidental contamination of
the water supply with oil or grease.
Among the diseases caused by competitive fungi in the
mushroom bed the white plaster mold (sometimes called
"flour mold") and truffles are the most troublesome. The
former is caused by a fungus, "Monilia fimicola" Cost.
and Matr., which produces a grayish spore dust through-

out the interior of the compost. When this fungus is
abundant in the beds the mushroom mycelium rarely
grows more than a few inches from the spawn piece and a
total crop failure often results. In some cases the origin
of serious infestation with this mold has been traced to
contaminated brick spawn. Usually severe outbreaks are
due to insanitary conditions around the mushroom house
or to a wet, soggy condition of the manure at filling time.
"The truffles disease is characterized by the development of cream-
colored wefts of fungus mycelium which appear under the side-
boards and in the manure at about the time of casing. Unlike the
plaster mold, the truffles fungus 'Pseudobalsamia microspora' Diehl
and Lambert seems to stimulate rather than prevent the run of
spawn in the early stages of the crop. A few weeks later, however,
when the truffles fungus matures and forms wrinkled fungus bodies
in the manure and on the soil, the parts of the beds infested with
truffles become barren and the mushroom mycelium almost com-
pletely disappears. The source of this fungus is not known, since
it has not yet been found outside of mushroom houses. However,
the nature of the fungus and the history of the disease suggest that
it lives in the soil and is carried into the house in the compost.
There is also some evidence that it may remain from one crop to
another in the bed boards and that high temperatures and an over-
wet condition of the manure favor its development. The spores are
probably distributed principally at the time of emptying the beds."

The chief pests causing commercial damage to mush-
rooms are the fungus gnats, mites, and springtails.
In general, the fungus gnats of the genus Sciara cause
the most injury to the mushroom industry. They are
prevalent in almost every type of mushroom house or
cave, since they usually enter in the compost when it is
taken into the houses. The larvae or maggots of these
flies cause injury both by destroying the mycelium in the
beds and by feeding on the small mushrooms, which they
completely devour in many instances. These maggots
can also render the large mushrooms unfit for market by
tunneling upward through the stem and cap. The adult
flies often transport injurious mites which attach them-
selves to the bodies of the flies from one mushroom house
to another and they also aid in disseminating some mush-
room diseases.
The mites, while not generally so prevalent as the
fungus gnats, are capable of causing serious losses once
they become established in mushroom houses. The mush-
room mite proper, "Tyroglyphus lintneri" Osb., feeds on
r'lar.l .by < i: i (; ml ll. fi wri'ly ai Isslstantllll .lit..n ) gi..l..?is, Killr.U ,.f :nto-
IIII)l y. (v .. S It 1> :I tw.li. -i f .A :ri4j-ulll trl .

the mushroom, producing dark pits which result in decay,
destroys the mycelium in the beds, and cuts off the feeder
root system so that the mushrooms do not mature, and
decreased yields result.
It is much more widely distributed, apparently, than
the mite. "Linopodes antennaepes" Banks, which has also
been found causing commercial damage to mushrooms in
several plants.
Springtails cause very little damage to mushrooms in
the East, but are one of the most serious pests with which
the growers operating in the sandstone caves of the
Northwest have to contend. While the species found in
the sandstone caves has never been described in the
United States and apparently is not present in the East,
it is doubtful whether it would cause a great amount of
damage in the modern eastern houses, since they provide
atmospheric conditions unfavorable to the insects' rapid
development and reproduction.

Because the mushroom mycelium, as well as the mush-
room itself, is extremely sensitive to most fumigants, it is
necessary to take certain precautionary measures before
placing the spawn in the beds. in order to prevent heavy
infestations by insect pests and subsequent damage.
In the course of the heat in the beds the temperature
will rise high enough, if forced air circulation is employed,
to either kill the insects in the compost or drive them to
the surface where fumigants can be used effectively.
Electric fans provide the necessary forced circulation of
air during the heat.
Two 16-inch fans will equalize the air temperature all
over the house and make the temperature in the compost
fairly even in all the beds. The various pests can then be
killed by fumigation while the temperatures are highest.
Calcium cyanide. scattered on the floor in the alley-
ways at the rate of 1 pound per 1,000 cubic feet of air
space has heretofore been most widely used, but the burn-
ing of sulphur, which is cheap and has a double role as a
fungicide and insecticide, is gradually replacing the use of
cyanide. Burning sulphur at the rate of 2 pounds per
1,000 cubic feet of air space while the compost is at its
greatest heat in the beds, and leaving the house closed for
five hours after all the sulphur has burned, has proven
very effective against any pests in the house at the time.

Results of yield tests indicate that this process has not
injured the compost for subsequent mushroom culture.
Results of hydrogen-ion determinations have shown
conclusively that the sulphur fumes do not penetrate
much more than 1 inch into the uncased compost and that
the surface compost is rendered slightly more acid than
it was before being fumigated. Hydrocyanic acid gas
penetrates the compost to the same depth.
To prevent possible infestation of the houses after the
compost has gone through its heat and has been fumi-
gated, the doors and ventilators should be screened with
30-mesh copper-wire cloth. To prevent rapid develop-
ment and multiplication of insects and mites the tempera-
ture of the house should not go above 55c F. while crop-
A dust consisting of 60 per cent pyrethrum powder and
40 per cent finely ground clay, used at the rate of 21/2
ounces per 1,000 cubic feet of air space, has proven very
satisfactory for control of the adult flies and does not
injure the mushrooms.

Comparatively little skill is required in picking mush-
rooms. They are usually gathered at a stage of growth
about 12 hours before the veil would normally rupture.
Mushrooms in the same stage of growth often range from
1 inch to 3 inches in diameter, so the principal considera-
tion is not the size of the mushroom but whether it has
finished growing in the closed form. Mushrooms are
pulled rather than cut. After a mushroom or clump of
mushrooms is picked, the fleshy stump is carefully re-
moved and the hole is usually filled with fresh soil. The
removal of these stumps is important, since their presence
in the bed favors the development of green mold in the
soil and the green mold prevents the formation of new
mushrooms in the moldy areas. Large numbers of button
mushrooms from one-eighth to three-eighths inch in
diameter die off, even on normal beds, presumably be-
cause of the crowding out or breaking of the mycelial
strands connecting the young mushrooms with their sup-
ply of nutrition in the compost. With a little practice
these mushrooms are easily distinguished from healthy
buttons and they should be removed from the bed for the
same reason that the dead stumps are removed.
Most of the mushrooms sold in the United States are
marketed fresh, although a well-established canning in-

dustry has developed in the last 15 years to take care of
the demand for canned mushrooms. Fresh mushrooms
are sold on the basis of weight, in the East in 3-pound
baskets and in the West largely in 1-pound paper cartons.
When packed fresh they are usually sorted according
to varietal characteristics, size, and freedom from blem-
ishes. In most large cities they are sold on a commission
basis through produce dealers. In smaller cities they are
sometimes shipped directly from the grower to hotels.
Shipment from surrounding states into Chicago is usually
made by express, whereas nearly all of the mushrooms
shipped from Pennsylvania into New York City are taken
directly from the grower to the commission dealer in auto-
mobile trucks.
Often both the grower and the consignee benefit from
the use of United States standards for mushrooms when
handling the best grade. Mushrooms may be graded and
the containers marked United States No. 1 provided they
contain good quality mushrooms larger than 1 inch in
diameter. They may be marked United States Small,
United States Medium, United States Large, and United
States Extra Large if they conform to the quality require-
ments under United States No. I and the following size
specifications: Small, under 1 inch in diameter; medium,
1 to 15:; inches; large, 15 to 3 inches; extra large, over
3 inches. Packages in any of these grades should contain
fresh mushrooms of similar varietal characteristics which
are not badly misshapen, are free from disease, insect
injury, open cap, spots, and damage caused by dirt, or
by mechanical or other means, and having stems properly
trimmed and not more than 1 '!. inches long. *
Mushrooms are canned in Pennsylvania, Delaware,
Ohio, Minnesota, and Colorado. Usually they are re-
ceived at the cannery and processed on the day they are
picked. Button mushrooms are preferred for canning.
These are sorted out on a moving belt, carried imme-
diately to vats where they are preheated until they have
shrunk about 40 to 50 per cent in bulk, placed in cans,
weighed, and processed.
A few growers have tried marketing dried mushrooms,
but this product has not seemed to find much favor with
the consumer and must meet the competition offered by
dried mushrooms from the Orient and southern Europe.
('opi] s .|o'fh latl l.st 'lI ited StaMls spli.ifi. ti Ions 'for uit shI room grades andil
Sizes '. il ulldI nL tlll Ihll illitlioln f ItI rillms indl thlIe perverlnlll ge of It lrllr an o1' (of
type'S. ri' ll 111' l Jl:lill-'l oIII rI' lllr st frnlll Ish rllllrtlu l o1 .\4 gri I". lhitparlllll.lll I .\Agrillnhurv. V i hinllgt I. (:.


Mushroom growers must meet many of the same eco-
nomic difficulties that confront the producers of other
perishable crops. The cost of production is difficult to
predict and the sale price is almost entirely out of the
grower's control. Although the cost of raising a crop is
largely fixed, the cost of producing a pound of mushrooms
often varies considerably from one crop to another, de-
pending on the yield per square foot of bed space. The
price differs from one locality to another and from one
season to another. In the East prices are usually some-
what higher during the summer than in the winter, be-
cause fewer mushrooms are grown in the summer. Warm
spells in the early fall and late spring may greatly in-
crease the supply of mushrooms for several days at a time
by raising the temperature in mushroom houses. The
temperature rise is reflected in an increased rate of growth
of the mushrooms and in the production of a larger pro-
portion of buttons. In congested centers of mushroom
growing this usually occurs in hundreds of mushroom
houses at the same time and the grower often finds him-
self in the untenable position of producing the most mush-
rooms when the price is below the cost of production.
If a yield of 1 pound per square foot is assumed, the
cost of producing mushrooms in eastern Pennsylvania in
1930 was about 26 cents a pound. This may be divided
as follows: Interest on investment, depreciation, and
upkeep of buildings, 5 cents; raw materials, 14 cents;
and labor, 7 cents. (Table 1.) The estimated cost of
manure may differ as much as 3 or 4 cents from one
locality to another; the interest and depreciation charge
may be reduced when abandoned buildings or caves are
used; and labor cost will vary in different localities and
in different years. Otherwise costs are fairly comparable
in different localities. In some localities spent manure or
"mushroom soil" is sold to truck gardeners, but this rarely
returns an income of more than enough to pay for hauling
it away.

Table 1--Estimated Cost of Raising Mushrooms in Chester County,
Pcnnsylvania, 1930

.l lshroi ,.ns 1"i'n
Yidhl Is

SI'.llilo 1 io ]' nll s

Interest on investment (6 per cent of $5,000
equals $300.00) $0.0214 $0.0143
Depreciation (5 per cent) .0178 .0119
Manure, at $5.25 per ton (for 70 square feet
of bed space) .0750 .0500
Freight on manure, at $1.25 per ton .0178 .0119
Hauling manure to house, at 60 cents per
ton .0085 .0057
Composting manure, three turns .0081 .0054
Filling house .0063 .0042
Emptying house .0060 .0040
Fumigating and disinfecting .0036 .0024
Heat and light .0113 .0075
Spawn and planting .0200 .0133
Casing .. .00401 .0027
Ventilation. watering. and miscellaneous .0050 .0033
Picking and cleaning beds .0266 .0222
Packing .0116 .0116
Baskets, wire. and pape,. at 5 cents per
basket .0166 .0166

Tot-.l .2596 .1870

The following cost information. based on the estimates
(made in 1930) of several commercial growers, was used
in calculating the detailed cost per square foot of bed
space shown in Table 1.
Cost of building a double house (approximately 14,000
square feet) in a row of 10 is estimated at $4,000 on a
basis of wood construction, 100 feet long, 6-foot beds six
high, including heating plant. Equipment for this unit.
including trucks, is estimated at $1,000.
Cost of composting manure is based on the turning and
watering of a 90-ton heap three times by hand labor with
six men in 27 hours, at 35 cents per hour. (A heap of this
size fills a 7,000-square-foot house.)
Filling a house of 7,000 square feet, by hand labor,
takes seven men 18 hours (at 35 cents per hour), and
costs $44.10.

Emptying a house of 7,000 square feet takes six men 20
hours (at 35 cents per hour), and costs $42.00.
The cost of fumigating a house of 7,000 square feet is
estimated at $25 for sulphur, pyrethrum, labor, etc.
The cost of heat and light is estimated at $80 for 7,000
square feet, using soft coal.
Spawning and planting cost is based on the use of one
bottle of spawn, costing 70 cents, for 35 square feet.
The cost of casing 7,000 square feet with soil from land
belonging to grower includes that of screening (requiring
20 man-hours at 35 cents per hour) and hauling and
casing (requiring five men 12 hours), and totals $28.
The cost of picking and cleaning beds is based on one
man picking four to six baskets per hour, at 40 cents per
hour (including cleaning the beds).
Ventilating, watering, and miscellaneous costs are esti-
mated at $35 for each 7,000 square feet.
Packing cost is estimated on the basis of 10 baskets per
man-hour, at 35 cents.
Except in isolated cities where one or two growers con-
trol the supply, mushrooms are sold on consignment and
the price received for them is based on the prevailing
values, as indicated by sales from receivers and whole-
salers or retailers. In New York and Chicago the receiver
charges a commission of 10 per cent for handling mush-
rooms. The white variety commands a better price than
cream or brown and large mushrooms bring a higher
price than buttons. On this market a higher average
price is maintained in the summer because of the greatly
reduced supply.
Canners specialize in high-quality button mushrooms
and often fix a purchasing price in the fall that remains
fairly constant throughout the winter.

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