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Bacterial Blotch – Pseudomonas tolaasii (P. fluorescens)
Yellow to brown lesions form on mushrooms. Typically, spotting occurs at or near
the edge of mushroom caps. Blotch occurs when mushrooms remain wet for a period
of 4 to 6 hours or longer after water has been applied. The bacterium is spread
in air-borne soil particles. Controls include lowering humidity and watering
with a 150 ppm chlorine solution (calcium hypochlorite products are used since
sodium hypochlorite products may burn caps). If the mushroom stays wet, however,
chlorine has little effect since the bacterial population reproduces at a rate
that neutralizes the effect of the oxidizing agent. Shiitake caps are affected
by a bacterial disease caused by Pseudomonas gladioli (Burkholderia gladioli).
Sanitation is a critical component of control measures.
Cobweb mold or Dactylium
Mildew (Hypomyces sp.)
A cottony mycelium grows over casing. When it contacts a mushroom, the mycelium
soon envelopes the mushroom with a soft mildewy mycelium and causes a soft rot.
It is also a parasite of wild mushrooms.
Cobweb mold is darker than mycelium... almost grey as compared to white. The
difference in color is sometimes hard to tell for somebody that hasn't seen them
side by side before. Cobweb has several other indicators... the one that sticks
out is the speed of growth. A small patch the size of a dime will spread to
cover an entire jar/casing in just a day or two. Cobweb is also very very fine
strands, while mycelium tends to be thicker ropes.
Cobweb mold is favored by high humidity. Control strategies include lowering
humidity and /or increasing air circulation.
Dry Bubble – Verticillium
This fungus causes superficial, cinnamon-brown lesions of the mushroom cap.
Lesions may coalesce into a brown blotch. A grayish bloom appears when the
fungus sporulates. Infection of the stem results in a bent and/or split stipe.
The second major symptom is a dry bubble – a small, puffball-like mass where the
mushroom should be. Spores of this fungus spread in the air on soil particles
and on flies. Symptoms occur 10 to 14 days after infection. Sanitation is the
most important control measure.
Green Mold - Trichoderma
harzianum, T. viride, T. koningii
Green mold caused by Trichoderma harzianum is characterized by an aggressive,
white mycelium that grows over the casing and onto mushrooms, causing a soft
decay. Masses of spores that eventually form are emerald green. Heavily infested
patches of compost are barren. This is currently the most important disease in
the U.S. Agaricus industry. Many farms spread salt on the compost in affected
areas when green mold is first recognized. Strict sanitation is essential.
Shelving, trays, walls, floors, etc. may be surface disinfested as a matter of
routine, but it is done with a sense of urgency following an outbreak of a
disease. Many commercial products are available for cleaning surfaces. The base
ingredients in these materials include chlorine, iodine, phenol, or quaternary
ammonium, among others. Surface disinfectants are used farm-wide, from equipment
sanitation to room washdowns to foot-dip solutions to picking basket prewash.
Other Green Molds may be better defined as indicators since they don’t seem to
be as aggressive as T. harzianum. These species of Trichoderma also sporulate on
the casing surface and may sporulate on infected mushrooms. These fungi indicate
that carbohydrates are available, possibly due to inadequate nitrogen
supplementation during Phase I or undercomposting. T. viride reportedly produce
toxins that dissolve mushroom cells walls. A wet compost low in ammonia prior to
pasteurization, flies, poor sanitation, anaerobiosis, and other factors
influence green mold. These fungi are common in sawdust and commonly occur in
the production of specialty mushrooms.
Trichoderma is often mistaken for Penicillium or
Aspergillus molds(and vice versa), being that all
three look very similar and are not easy to tell appart without the use of a
Sime pictures underneath possibly show any of the three genuses out of the
Cinnamon Brown Mold –
Chromelosporium fulva (Peziza ostrachoderma)
The color of this mold ranges from yellow gold to golden brown to cinnamon
brown. It grows rapidly in circular patches. It is very common in soil, and
flourishes on damp wood. Areas in compost overheated during spawn run may be
colonized. Improperly conditioned compost will also support growth, but it is
most commonly known as a recolonizer of overly pasteurized casing, possibly
living on dead microorganisms. It often occurs on sterilized soil. Sexual
fruiting bodies may appear several weeks after the first appearance of the mold.
Spores are airborne.
Lipstick Mold –
Sporendonema purpurescens (Geotrichum candidium)
This fungus colonizes compost or casing. As spores mature, the color of the mold
changes from white to pink, to cherry red, and finally to dull orange. It is
slow growing. Spores spread in air, during watering, and on pickers. The
lipstick mold utilizes certain fats in the compost. It is an uncommon problem.
Control is centered around sanitation.
Red Bread Mold – Neurospora
Commonly to occasionally seen on agar and grain. Neurospora is fast growing,
sometimes taking only 24 four hours to totally colonize a media filled petri
dish. It is ubiquitous in nature, occurring on dung, in soils and on decaying
plant matter. Since this fungus grows through cotton stoppers or filter discs, a
single contaminated jar, though sealed, can spread spores to adjacent spawn jars
within the laboratory. This condition is more likely if the filter discs or
cotton plugs are the least bit damp; or if the external humidity is high.
Furthermore, Neurospora spores germinate more readily at elevated temperatures.
The pink mold seen in mushroom culture is most frequently Neurospora sitophila,
a pernicious contaminant that is difficult to eliminate. All infected cultures
should be removed as soon as possible from the laboratory and destroyed. A
thorough cleaning of the laboratory is absolutely necessary. If contamination
persists, remove all spawn and start anew.
Yellow Mold – Sepedonium spp.
This white, sparse mold grows in the compost during spawn run. With age, it
turns dull yellow to tan. Spores are airborne. Thick-walled spores may survive
peak heat. The mold colonizes compost considered ideal for spawn growth.
Black Whisker Mold – Doratomyces spp.
This fungus produces black powdery spores that appear as smoke when disturbed.
This mold indicates the presence of certain carbohydrates in the compost at
spawning time. It also indicates that the straw has been incompletely
caramelized or underheated in Phase I (therefore, carbohydrates are in a form
easily utilized). The proportion of carbohydrates, particularly cellulose, may
be too high. The black whisker mold is also present in compost that overheated
during spawn run. Simple carbohydrates are utilized by this fungus but it can
also utilize lignin. Doratomyces, Aspergillus, and Penicillium produce copious
numbers of spores and may cause respiratory problems (nasal and throat
irritation, chest congestion, breathing difficulty, etc.).
Molds – Penicillium spp.
Abundant blue-green spores are produced on the surface of the substrate. Similar
to Aspergillus. Favorable conditions parallel those
for the black whisker mold. Penicillium spp. utilize simple
carbohydrates, as well as cellulose, starch, fat, and lignin. These fungi are
very common on specialty mushrooms and are one of the chief concerns in agar and
grain culture. Spores are airborne and ubiquitous.
Black Mold (also Yellow Mold and others) – Aspergillus sp.
Very common in agar and grain culture, and in compost making. Found on most any
organic substrate, Aspergillus prefers a near neutral to slightly basic
pH. Well used wooden trays and shelves for holding compost are frequent habitats
for this contaminant in the growing house.
Species range in color from yellow to green to black. Most frequently,
Aspergillus species are greenish and similar to
Aspergillus niger, as its name implies, is black; Aspergillus flavus
is yellow; Aspergillus clavatus is blue-green; Aspergillus fumigatus
is grayish green; and Aspergillus veriscolor exhibits a variety of colors
(greenish to pinkish to yellowish). These molds, like many others, change in
color and appearance according to the medium on which they occur. Several
species are thermophilic.
Some Aspergillus species are toxic. Aspergillus flavus, a yellow
to yellowish green species, produces the deadly aflatoxins. A. flavus
attacks cottonseed meals, peanuts and other seeds high in oil that have been
stored in hot, damp environments. Of all the biologically produced toxins, the
aflatoxins are the most potent hepatacarcinogens yet found. The toxicity of this
species was largely unknown until, in 1960, 100,000 turkeys mysteriously died
from an outbreak of this disease in Great Britain.
Since A. flavus grows on practically all types of grain, this species is
of serious concern to mushroom spawn producers. Careful handling of any molds,
particulary those of the genus Aspergillus, should be a primary
responsibility of all managers and workers in mushroom farms.
Aspergillus fumigatus and Aspergillus niger, two thermotolerant
mesophiles, are also pathogenic to humans in concentrated quantities. The
affliction is called aspergilliosis or "Mushroom Worker's Lung Disease".
Spent compost is the most frequent source of Aspergillus fumigatus.
Fungus gnats (Sciarids) (Lycoriella spp.) and phorids (Megaselia
Adults are small (1/8 inch long), fragile grayish to black flies with long,
slender legs and thread-like antennae. Their wings are clear or smoky-colored
with no pattern and few distinct veins. Larvae are clear to creamy-white and can
grow to about 1/4 inch long. They have shiny black head capsules.
They are attracted to the mushroom crop and their larvae feed directly on
mycelium, swarm over the mushroom, and tunnel into the developing or developed
mushroom. Tissues that have been physically damaged by flies often become
colonized by bacteria which cause soft rot, thereby accentuating the problem.
Controls include strict sanitation and general farm hygiene. For example, the
grow room must be air tight. Fresh air that is used is filtered. Even a small
crack will serve as an entry for the flies. Most farms use sticky tape or some
other method that allows monitoring of populations. A biocontrol using nematodes
offers effective control when populations of flies are low. In addition to the
damage which fly larvae cause by eating mushroom mycelium or killing pins, the
adults also carry diseases such as Verticillium, Mycogone and Cobweb.
Many mites are commonly found in straw and manure, most species are beneficial
to mushroom growing as they feed on eelworms and other mites, although some can
Mites, like fly larvae, may feed on mushroom mycelium and on the mushrooms,
where they can cause surface discoloration. They may also live on other fungi
(weeds and indicator molds) found in mushroom culture. One example is the red
pepper or pygmy mite (Pymephorus spp.). These mites are commonly
associated with Penicillium and Trichoderma molds, upon which they
feed. Pygmy mites do not feed on Agaricus. These mites have the ability
to change into an intermediate stage called a hypopus, wherein they develop
flattened bodies and a sucker plate with which they attach to moving objects,
like flies. Mites at this stage swarm on top of mushrooms.
1. Tarsonemid mite
These mites are pale brown and are so minute that they are only visible with the
aid of a microscope.
They cause damage by feeding entirely on hyphae of mushrooms and the grower will
know if he has these mites present, as the base of the stem of the mushroom will
show a reddish brown discolouration. Where severe infestations occur the whole
base of the mushroom may be detached from the growing surface.
1. As with eelworms little can be done when mites are present in the growing
house, therefore efficient composting and peak heating must take place to ensure
that they are killed during the pasteurisation process.
2. Good hygiene should be practised around the farm, especially in the clearance
of crop debris.
2. Tyroglyphid mites (Tyrophagus spp)
These mites can be identified as they are slow moving, translucent, with long
hairs on their bodies.
If these mites are present in abundance they eat small pits in the caps and
stalks. These pits then suffer from bacterial decomposition, which breaks down
tissues just below the surface. This results in the skin collapsing which leaves
an open pit. Tyroglyphids may also feed on mushroom mycelium, where they are
present in large numbers, crop reductions can be caused.
Mites usually gain entry into the compost by clinging onto Sciarid flies when
the mites are the migratory stage. These migratory stages are normally produced
when mites become overcrowded.
The mites should not be a problem where efficient composting and peak heating
takes place. Organic debris should not be allowed to accumulate around the farm
as it provides a breeding ground for mites.
3. Red Pepper Mites (Pygmephorous spp)
These mites are not regarded as primary pests, their presence is usually an
indicator that Trichoderma (green mould) is present in the compost. These mites
feed on various weed moulds but not mushrooms, thus their presence indicates
that the compost is unsatisfactory.
The mites are yellowish-brown in colour, 0.25 mm in length and have a flattened
appearance, they also are capable of rapid rates of reproduction.
As already stated these mites are secondary pets and they often swarm on the
casing and mushroom surfaces. Where this happens their presence makes the
mushrooms unsaleable. These mites can also spread spores of Trichoderma from bag
Nematodes – Aphlelenchoides composticola and Ditylenchus
These nematodes are common inhabitants of most agricultural soils. Symptoms
include a degeneration of mushroom mycelium and failure of mushrooms to form.
Normally, an infestation is noticed at the time of third break. Mycelium in
affected areas is completely destroyed and as the compost decomposes, it turns
black and a medicinal odor is detectable. An effective Phase II is the primary
Several disorders have abiotic origins. Common ones include:
Browning – tyrosinase (phenolase)
is the main enzyme responsible for browning in Agaricus. Calcium chloride in
irrigation water decreases bruising by increasing the integrity of vacuole
membranes (thus, tyrosinase is not released).
Flock, hardcap, and open veil
physiologically induced malformation of cap and gill tissue. Cap opens
prematurely. Causes include some diseases, petroleum based materials, and
genetic abnormalities. Hollow core and brown pith – related to water stress, but
exact factors unknown. Long stipes and small caps – insufficient light and/or
condition where pink gill tissue, often with a porous appearance, develops on
the surface of a mushroom cap. The cause has been attributed to contamination by
petroleum based materials.
the natural reaction of the mushroom cap to dry air.
dense mycelial growth without fruiting. Stroma occurs if spawn is mishandled or
exposed to harmful petroleum-based fumes or chemicals. It also occurs in dry
mushroom exudes water from cap. The cause is not known, but it is seen in
low-moisture compost and high-moisture casing.