Mushroom Growing

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Mushroom Growing

Of the manyspecies of edible mushrooms which grow infields and woods, only one, Agaricus bisporushas been developed as a cultivated crop in theUnited States. Because of the variety of condi-tions under which fungi grow naturally, it mightbe assumed that commercial production wouldbe a simple process but nothing could be furtherfrom the truth. No other crop is as exacting inits requirements. Profitable production requiresconstant attention to maintenance of favorableconditions and eternal vigilance against theinroads of insects and diseases.

Because the mushroom is a fungus and lackschlorophyll, it cannot carry on photosynthesisand must depend upon non-living organicmatter for its nutrition. Also, because it belongsto a lower order of plants having no true roots,stems or leaves, it produces no flowers or seedsand reproduction depends upon spores. Hencemushroom growing is not a matter of plantinga seed to produce a plant.

The spores are borne on the gills on the under-side of the mushroom cap and one mushroomproduces millions of spores. Given a favorableenvironment, the spores develop a threadlikemass called mycelium or spawn, which in turn,under the proper conditions, develops thefruiting bodies which are edible mushrooms.

The early steps in this process, called "spawnmaking," are carried on in a laboratory undercarefully controlled and sterile conditions. Thespores are collected by a trained technician andplaced on a potato-dextrose-yeast agar forgermination. They are later transferred tobottles containing an organic medium such as tobacco stems, kafir corn, wheat or rye forcontinued growth. The bottles are kept at 75° F.until the threads of mycelium have covered thegrain or other medium after which they areplaced under refrigeration until time for use.

Because conditions for mycelia] growth arcalso favorable to growth of molds and bacteria,the bottles are checked frequently and any whichshow contamination are discarded.

Only the largest producers of mushroomsprepare their own spawn; most growers pur-chase their supplies from companies whichspecialize in that function.

Before getting his spawn supply, the growerprepares his houses. A "standard" mushroomhouse, usually built of cinder block, is 64 ft. x 20ft. and contains 2 tiers of beds with an alleybetween. Each tier is 6 beds high, giving a totalbed surface of approximately 4000 sq. ft.Mushroom houses are now built as "doubles,"that is, each house is wide enough for 4 tiers ofbeds. Because light is unnecessary for growth,the house has no windows. Temperature andair circulation are important, however, and aseries of ventilators is built into the roof.

The organic matter in which the myceliumgrows is called compost. In the early years ofcommercial mushroom production, compostwas almost entirely horse manure. FollowingWorld War II, because of the scarcity of horsemanure, growers adopted "synthetic compost"which is made of hay and chopped corn cobssupplemented with brewers' grains and gypsumand small amounts of ammonium nitrate ormuriate or potash.

Since 196o a decreasing availability of corncobs and an increased number of race trackswith available manure have brought about acombination of "synthetic compost" and horsemanure for mushroom compost.

Before being placed in the house, the compostmust go through a curing process during whichit is turned several times and water added. Inthis way it is broken down by the bacteriapresent and is both chemically and physicallyconditioned for the growth of mushrooms. Thecomposting process requires from 1-3 weeksdepending upon the material used and the rateof bacterial action. Over-composting or under-composting can have adverse results on themushroom crop. The experienced grower knowsby the appearance and feel of the compost whenit is ready to go into the house; no definite rulecan be laid down for this process.

After the beds have been filled to a depth of6 or 8 in., the compost must go through apasteurization period known as the "sweat out"or "cook out." The house is closed tightlyexcept that doors are opened at intervals toreplenish the supply of oxygen. Fans are installed to aid in bringing all parts of the houseto a uniform temperature. The heat generatedby bacterial action in combination with themoisture, causes the temperature in the compostto rise and the resulting pasteurization bringsabout a final conditioning as well as killinginsect and disease organisms which have comeinto the house in the filling process.

The "cook out" is a critical step in thepreparation for a mushroom crop. Muchdepends upon the condition of the compostwhen it is put into the house. The bacterialaction depends upon the moisture and carbo-hydrate content of the compost ; if conditionsare not right, the temperature may rise toorapidly or too slowly. If the temperature doesnot go high enough disease organisms are notkilled. On the other hand, an extremely hightemperature can cause chemical changes in thecompost which can result in a poor crop. Sinceair temperature is no indication of the composttemperature, thermometers or Thermo-couplesare placed in the beds and checked fre-quently.

A uniform compost temperature of 140° F.throughout the house is considered sufficient tokill animal pests and molds. As the compostheat approaches this point, heat is usually addedin the form of steam to equalize the air tempera-ture and the bed temperature and the house isheld at this point for from 4 to 6 hours. Thetemperature is then allowed to drop slowly,preferably not more than 5° per 24 hours.

When the compost is placed in the beds, ithas a strong odor of ammonia. By the time thetemperature has dropped to 125° F. after thepeak heat, no ammonia should be noticeable.The compost temperature is then allowed todrop to 75° F. before spawning. The entire"cook out" requires from 7 to to days.

The spawn is then broadcast on the beds andthe mycelium grows into the compost in whitish-gray threads. During the "spawn running"period, the temperature is maintained at notmore than 75' F. and the compost should have awater content approaching 70%. Water is appliedas a fine spray rather than as a heavy stream andnot in quantities that will cause the compost tobecome soggy. Transparent plastic is sometimesplaced over the beds to maintain a satisfactorymoisture level in the compost during the spawnrun. From 2 to 3 weeks are required for thespawn to grow through the compost.

While the mycelium will grow in the compostit will not develop into the fruiting stage andproduce mushrooms until a thin layer of soil(called "casing soil") has been placed on top ofthe compost.

Preparation of the casing soil is again a mostcareful process. Since the mushrooms derive

no nutrient from the soil, the physical charac-teristics of good casing soil are more importantthan its chemical composition. It must holdwater without becoming waterlogged and mustremain friable on the beds without "caking."Topsoil meets these requirements better thansubsoil. This means that in areas of concentrat-ed mushroom growing, long-range programs ofrebuilding topsoil must be planned.

Although the chemical content of topsoil isnot important, its degree of acidity affects thecrop. It should test between 7.z and 7.8 on theplI scale. Spawn laboratories maintain soil-testing services for their customers. If the pHtests below 7, lime is added. Mushrooms tend toproduce acid in the soil and the addition of limeneutralizes the acids and aids in preventing thegrowth of green molds.

The soil is screened in the field to removestones and debris and is then transported to thewharf at the mushroom house where it mustundergo sterilization.

One cause of crop failure in the mushroomindustry is the presence of nematodes which arepresent in all soils and all raw compost. At least2 species are especially injurious to mushroommycelium. The soil as it comes from the fieldmay also be infected with organisms which causemushroom diseases known as "bubbles,"verticillium spot, and "mat" disease (allfamiliar terms to the mushroom grower butmerely names to the inexperienced).

heating the soil to i8o` F. by passing livesteam through it will destroy nematodes as wellas other animal and disease organisms. Somechemicals such as chioropicrin have also beenfound effective and chemical sterilization of soilhas replaced steaming to some extent. Aftersterilization, the soil is placed in a clean bin oron a concrete wharf and covered to preventrecontamination.

When the mycelium has grown through thecompost, about t in. of soil is placed on top ofthe beds and leveled off. Again there must beconstant attention to watering, temperatureand ventilation.

Mushrooms begin to appear as "pinheads"about 3 weeks after casing. The temperaturemust be held at no more than 70° F. and prefer-ably between 50' and 65" F. The lower tempera-tures improve mushroom production and dis-courage the growth of insect and diseaseorganisms.

Throughout the growing period the growermust be alert to invasions by disease or insects.Optimum conditions for mushrooms arc alsofavorable to growth of molds and weed fungi,hence the precaution to prevent contaminationby spores in spawn, compost and soil. Mal-formed or diseased mushrooms are removed

Mushroom Growing716

from the beds and destroyed to reduce spread ofinfection.

Animal pests which create problems arespringtails, several species of mites and 3 speciesof flits peculiar to mushroom-growing areas.Adult flies are a means of spreading mold sporesand nematodes from one area to another and thelarvae of some species cause damage to themycelium and the mushrooms.

Because some insecticides injure the mush-rooms or inhibit their growth and some othersarc too poisonous to use on food crops, it isdifficult to treat insect infestations after mush-rooms appear. Hence, it is important to takeevery possible precaution in the proper manage-ment of the compost and casing soil. Othersteps in control include sterilization of the housewith steam before removing spent compost atthe end of the crop, proper disposal after re-moval and elimination of trash piles and otherpossible breeding places on the premises.

Mushrooms grow in somewhat rhythmiccycles called "breaks." The heaviest productioncomes from the first 2 "breaks," but bedsproperly adjusted for moisture and temperaturewill continue to produce mushrooms for about3 months.

During the production period, picking mustbe done every day, although it requires from 6to to days for a mushroom to grow to market-able size. Average production is 21: to 21 lbs. persq. ft.

In southeastern Pa., which is the mostconcentrated area of production in the UnitedStates, it has been customary to fill the houses inSept. for the first crop, then refill for a secondcrop about Jan., thus ending the growingseason with the advent of warm weather. Theincreased use of cooling systems makes itpossible to start the first crop earlier and extendthe second crop later into the spring months;or by limiting the picking to the most productiveperiods, it is possible to have 3 crops a yearinstead of 2. Few growers, however, find itprofitable to use air conditioning for a mid-summer crop.

In western Pa., a large mushroom-growingenterprise is carried on in caves from whichlimestone was formerly mined. Here, as well as insome large plants in other parts of the country, asystem of moveable trays is used instead of theconventional stationary beds. The tray systemlends itself more readily to filling, spawning andcasing by mechanical means. Because the cavesmaintain a year-round temperature of approxi-mately 56° F., special rooms arc maintained forthe "cook out" and spawn run which must takeplace at higher temperatures. It is possible underthese conditions to produce mushroomsthroughout the year by replacing the trays in the

caves every 5o days. This type of operation,however, is the exception rather than the rule.

Because mushroom-growing dots notrequire a large acreage, it must not be assumedthat the business can be started with littlecapital. The initial investment for one doublehouse can quickly amount to more than Sio,000exclusive of cooling equipment and necessarymachinery for operation. It is a businessrequiring complete understanding of all of thenecessary steps and is not recommended for theinexperienced.

Long considered a delicacy used primarily toenhance the flavor and attractiveness of otherfoods, mushrooms are known to contain smallamounts of the vitamin B factors, thiamin andriboflavin, and are somewhat higher in mineralsthan many vegetables. They are also low incalories since they have a high water content.Earliest commercial production in theUnited States was in the vicinity of New YorkCity and Long Island about 188o where theywere mostly grown in caves and cellars. About1885 some florists at Kennett Square, Pa.,tried growing mushrooms beneath the benchesin their greenhouses and in 1896 the first houseswere built in that area for the specific purpose ofgrowing mushrooms. From this beginning,southern Chester County, some 3o miles fromPhiladelphia, became the center of the industryin this country. There are sizeable operations inupper New York State, the Midwest, and on thePacific Coast, but Pa., continues to account forsome 6o% of the national production. Of some800 growers in the country, 600 are located inPa.

National production is in excess of16o,000,000 lbs. annually. Approximatelygoes to the fresh market, the balance finding itsway to the consumer as canned mushrooms,soups and sauces.

Since 195o, an international congress hasbeen held every 3 years under the auspices of theInternational Commission on MushroomScience, at which time scientists from all parts ofthe world present the results of research beingcarried on relative to cultural methods, im-provement of spawn cultures, and control ofadverse factors affecting the industry.

VIOLET K. TYSON

Insect Pests

The maggots of fungus gnats or mushroomflies eat the stem and the cap and ruin them asfood. Springtails are small jumping insectswhich feed on decayed vegetable matter and areattracted to manure. They eat cavities in thecap and gills of the Mushroom and are verydestructive when abundant. Mushroom miteswhich are white with soft bodies cat the roots(mycelium) and chew cavities in the stem and

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cap. Sowbugs ai-alegs which often a' a -Heating the ma.the spawn, kills n-.

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K. TYSON

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cap. Sowbugs are small gray animals with tolegs which often damage the spawn and buttons.Heating the manure to 135' F., before sowingthe spawn, kills most of the pests.

Sprays and dusts of insecticide # 27 andfumigation with insecticide #40 have beeneffective against the gants. Insecticides # isand #9 are approved for use on mushroomsunder specific conditions and advice from localauthorities should be obtained before using anyof the newer pesticides.

MUSHROOMS. These are the fruiting bodies ofplants which have no chlorophyll. They do notmake food from carbon dioxide, nitrates andminerals but with water and proper temperaturethese plants feed on organic matter which hasalready been manufactured by chlorophyll-containing plants or animals. The part of theplant which grows underground in long, minutemany-branched threads is the mycelium, or"spawn" as the commercial growers call amass of them. These give off the enzymes whichdigest whatever food materials there are in themedium in which they grow. When this digestedmaterial is dissolved it is absorbed by themycelia and hence supplies the materials forgrowth.

Mushrooms then are the fruiting bodies ofcertain fungi. There are over 3000 mushroomspecies in the United States. In nature theyfeed on decaying logs and organic matter inthe soil, or they feed on decaying animal matter.When there is no more food of the type theyneed, they cease to grow and die. In the interim,however they produce the visible fruiting bodiesor mushrooms, which in turn produce sporesthat are eventually spread by the wind. If thesefail in a suitable place, and temperature andhumidity arc at an optimum, these start togrow and eventually the growing mycelia willagain produce the mushrooms that are visibleabove ground.

"Fairy rings" are produced by certain fungiin this manner: The spore falls on an areawith food and the mycelia advance at a certainrate in all directions from that spot. Then,when the time comes for producing the fruitingbodies, they are all produced (above the groundof course) in a very definite ring with the centerof the circle being where the original spore wasdropped. It has been estimated that in certainplaces where there is plenty of food for theseorganisms so that they continue growth that bythe size of the circle of fruiting bodies and itsenlargement each year, some of these coloniesmay have been growing in the same location for400 years.

Moisture, quite a bit of it, is necessary forgrowth and the production of the fruitingbodies. Mushrooms are often very specific

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concerning the type of material they live on.Some live on decaying logs, and some of theseattack the log soon after it begins to dis-integrate then die when their specific foods areused up. Then come others, which could notlive off the log at first but can after it has beenworked on awhile by the primary fungus. Otherscome after this. Some live on the rotting leaveson the forest floor and since these arc re-plenished year after year these mushrooms arealways found in such places. Others may be sospecific in their demands that they live only on acertain kind of log, Poplar, Pine or Maple. So itis seen that in hunting mushrooms one mustknow something of their specific requirementsand then look in likely places.

Some fungi become attached to the roots ofcertain trees and the association can be beneficialto both. These mycorrhiza can only live in thiscombination. Mushrooms are identified only bytheir fruiting bodies and hunting mushrooms ina warm damp season is more productive than ina cold dry one.

It is extremely important that when onebegins collecting mushrooms to eat, onedefinitely knows the difference betweenpoisonous and non-poisonous species. There isno sure-fire rule of thumb—one must be able toproperly identify them. In an excellent publica-tion called "The Mushroom Hunter's FieldGuide" by Alexander H. Smith, published byThe University of Michigan Press, Ann Arbor,Mich., in 1963, there arc descriptions of 188 ofthe most common mushrooms, poisonous andedible, together with 200 black and whitepictures and 89 color plates. Even this authorstates that after all this is only a field guide, andeven with description, black and white photo-graphs as well as color photographs, it ispossible to make a costly misidentificationmistaking a poisonous sort for one that is edible.Before hunting and eating mushrooms gatheredin the wild, one would do well to studycarefully the remarks made in a book such asthis, then make doubly certain the onesselected for eating are definitely identified asedible species. It is interesting to note that theauthor lists 119 as edible; 15 as doubtful; 3o asnot recommended; and 24 as poisonous. Themost poisonous of all is the Destroying Angel(Amanita verna).

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