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Edible and Medicinal Mushrooms: Technology and Applications, First Edition.
Edited by Diego Cunha Zied and Arturo Pardo-Giménez.
© 2017 John Wiley & Sons Ltd. Published 2017 by John Wiley & Sons Ltd.
Mushroom production represents one of the best examples in agriculture where pests can be
controlled without the use of chemicals. Because mushrooms are typically cultivated in a pro-
tected environment, direct control over its pests is quite achievable. The fundamental princi-
ples necessary to manage pests, diseases, or other molds are the recognition of the problem
through its symptoms and signs and an understanding of the actual organism responsible, its
life cycle, and spread.
In mushroom production, the principal pests are flies, mites, and nematodes. Other pests
such as mice, spring tails, thrips, beetles, and sowbugs have been reported (Snetsinger, 1972).
This chapter will focus on pests associated with commercial production of Agaricus bisporus
and their management.
11.1 Fly Pests
Commercial mushroom fly pests include three dipteran families: Sciaridae, Phoridae, and
Cecidomyiidae (see Chapter16, Figure 16.11). Each family can cause significant yield or quality
loss and vector mites, nematodes, and diseases on commercial farms. The dominant problem-
atic species display regional, annual, and seasonal variations.
11.1.1 Dark‐Winged Fungus Gnat
Sciarids are commonly known as the dark‐winged fungus gnats, sciarid flies, big flies, or
mushroom flies. The predominate fly species in North America is Lycoriella ingenua (Dufour)
(syn. L. mali, L. solani) while in the UK both L. castanescens (Lengersdorf ) (syn. L. auripila)
and L. ingenua are mushroom pests with L. castanescens being the more serious pest there
(Menzel and Mohrig, 2000; Fletcher and Gaze, 2008). Bradysia spp. are also pests of mush-
rooms in other parts of the world (Fletcher and Gaze, 2008). Only Agaricus bisporus is subject
to severe attack by this gnat but it also will breed on oyster and shiitake mushrooms. In general,
the dark‐winged fungus gnat can be found in greenhouses in both soilless and soil mixtures, in
composting debris such as leaves, and outdoors in wild mushrooms.
Insect, Mite, and Nematode Pests of Commercial
Danny Lee Rinker
University of Guelph, Guelph, ON, Canada
Edible and Medicinal Mushrooms
Dark‐winged fungus gnats can be found on any mushroom farm, but direct yield losses occur
only when the gnats go unchecked. Larvae of this fly are general feeders, consuming mush-
room compost, mycelia, spawn grains, mushroom primordia (pins), and carpophores. When
mushroom primordia are small, up to about 1.5 cm diameter, the larvae can consume the entire
internal contents. The mushrooms will appear glossy and light brown, and the small carpo-
phore may be completely perforated and, when picked, the tissues crumble. Carpophores that
are larger when attacked show black necrotic areas in the stipe where the larvae made feeding
galleries. Some larvae do not tunnel into the stipe but consume the mycelia at the base of the
stipe, in which case the mushroom does not develop normally. Generally, little direct damage
from this gnat will be evident on first‐flush mushrooms because the fly population has not
developed sufficiently. However, second‐ and subsequent‐flushes may show some damage
from larval feeding. Kielbasa and Snetsinger (1980) established that 108 females per square
meter were required at spawning to set up conditions for economic losses.
Perhaps its greatest impact is as a vector of mushroom pathogens, such as dry bubble dis-
ease (Lecanicillium fungicola (Preuss) Zare) and Gams [syn. Verticillium fungicola (Preuss)
Hassebrauk, Verticillium malthousei (Preuss) Ware]) or green mold disease (Trichoderma
aggressivum Samuel and Gams f. aggressivum and T.a. f. europaeum) (syn. Trichoderma
harzianum biotype Th4 or Th2, respectively), from diseased to clean areas in the same
production room or to clean crops on the farm.
Eggs of this fly (family Sciaridae) measure 0.25 by 0.15 mm and are smooth, oval, white, and
translucent. Mature larvae are about 7 mm in length, have a white, translucent body and a
black head capsule (Figure 11.1). Pupae are about 2.0–2.5 mm in length, are white at first but
turn black prior to eclosion. Adult males and females measure between 2 and 3 mm in length;
most often they can be found near a light source. The adult wing has a distinctive forked and
Figure 11.1 Sciarid flies, adult. Credit: Photo graciously provided by F.J. Gea and M.J. Navarro (CIES, Quintanar
del Rey, Cuenca, Spain). (See color plate section for the color representation of this figure.)
11 Insect, Mite, andNematode Pests ofCommercial MushroomProduction 223
188.8.131.52 Life History
This fly usually invades the mushroom crop at or near the time of spawning. This can occur in
single or multi‐zone systems. After invasion, adults may oviposit on mushrooms, on compost,
or in the casing soil, laying eggs singly or in small groups. The larvae have four instars and may
feed on the spawn grains, mushroom compost, mycelia, and mushrooms.
Within four hours of emergence, female gnats are sexually receptive and usually will have
mated. Egg‐laying begins soon afterward. Female flies are strongly attracted to odors emanat-
ing from the mushroom facility, particularly as the compost cools after the pasteurization and
conditioning phases. Peak fly‐invasion generally occurs within four days of spawning. Flies
always seek the nearest site for oviposition; in commercial mushroom operations, this is
usually nearest to doors of the production facility. Larvae developing in the surface layer of
compost, which is later to be cased, will move through and pupate at or near the surface of the
The development times from egg to adult, survival, and fecundity are temperature depend-
ent. The optimum temperature for development and maximum survival is 18.3°C. If flies enter
at spawning, then the first‐generation adults will emerge about three weeks later. At higher or
lower temperatures, mortality increases; it may be as much as 33% at 27°C. Female fecundity is
inversely affected by temperature, such that an average female will lay 160 eggs at 12.8°C, but
only 63 eggs at 26.7°C. (MacDonald and Kielbasa, 1977; Kielbasa and Snetsinger, 1978). The
biology is not only dependent on temperature but also on the species on which L. ingenua is
feeding (O’Connor and Keil, 2005).
The number of generations on a mushroom farm depends on the mushroom crop length.
Multi‐zone systems harvesting only two flushes may only have one complete generation during
each cropping cycle. However, if the crop is extended beyond two flushes then two or more
complete generations are possible.
184.108.40.206 Management Strategies
The movement of sciarid flies from one production room to another or from one mushroom
farm to another is accomplished mainly by unassisted adult dispersal and the persistence of the
insects, which will crawl through any crack or crevice into the mushroom production facility.
In temperate climates in the winter with outside temperatures below 7°C, sciarid populations
are lowest since migration and outside reproduction is limited due to temperature. Although
the threat of fly problems is minimal at this temperature, sciarids can move from one produc-
tion room to another through corridors, lofts, mezzanines, or outside the building; and they
have been seen on the surface of snow 7–10 m away from production rooms where they have
emerged. During warmer months, they will move from building to building, and to farms
several kilometers distant.
Under conditions of poor sanitation and hygiene, eggs, larvae or flies can enter the room on
equipment that was not cleaned from previous spawning or casing procedures. In addition, by
leaving spawn overnight in a fly‐infested corridor, an infestation of flies can be introduced into
the production room through the spawn or boxes. Growers who obtain mushrooms from other
growers run the risk of introducing fungus gnats along with diseases, if other farms have a fly
When an invasion occurs, the size of the initial population and predicting its future size are
important considerations. Monitoring gnat populations provides this information, but such
factors as climate, disease, immature and adult insect populations, and growing practices are
also important (Wuest and Bengston, 1982).
Edible and Medicinal Mushrooms
The adult stage of the dark‐winged fungus gnat is the main concern when monitoring on a
commercial mushroom farm. Monitoring for adults is accomplished by means of a fluorescent
or black light as a fly attractant and a sticky surface to trap the flies (Wuest and Bengston,
1982). Yellow sticky cards are less attractive than a light source.
All production rooms should have a monitor regardless of farm system. Some monitor loca-
tions within the room may capture more flies than another. In a single‐zone shelf farm or in
phase II tray system, the monitor should be placed in the room prior to the compost cool‐down
period when air temperature reaches 43°C. Monitoring is more challenging for multi‐zone
farms with phase II and spawn‐run tunnels. If the tunnel is totally enclosed in a building, which
is the most desirable, a monitor should be placed in the work area. Some farms have placed
monitors inside spawn‐run tunnels at filling for monitoring during spawn‐run. Monitors posi-
tioned outside, where flies normally roost, and in the picking corridor, provide an indication of
the background or endemic population level and measure the effectiveness of an outside or
corridor control program. In cool weather, the picking corridor may serve as a significant
bridge for fly movement between rooms.
Accurate fly catches should be recorded daily to evaluate control programs and to design
future strategies. Threshold levels at different stages of a crop vary. For this reason, growers are
encouraged to determine their own economic threshold levels. On single‐zone farms, one fly
on a monitor has been considered a sufficient threshold at spawning for action.
220.127.116.11.2 Cultural Practices
Multi‐zone systems in North America are harvesting for only two flushes. Shortening cropping
cycles have been demonstrated as a viable economic management practice and ancillary to this
fly and disease problems are reduced. Rapid cool‐down at the end of phase II reduces the time
available for fly invasion. Higher temperatures occur in the compost during spawn‐run and
after casing, compared to the harvest period. Shortening the spawn‐ and case‐run prolongs fly
emergence in the cycle of the crop’s phenology. In general, less fly problems will occur if the
spawn‐run is short.
Fly control at the end of a crop is just as important as control during spawn‐run. Growers
should heat‐treat the old compost at 60 to 65°C for 8–12 hours to kill flies at all stages of devel-
opment; these conditions will also kill most disease‐causing fungi and bacteria. (Note that this
temperature and duration is not sufficient to eradicate virus disease and especially green mold
disease (Trichoderma aggressivum f. aggresivum).) A crop may have to be terminated earlier
than the schedule dictates to ensure that the population of emerging flies can be controlled
prior to its spread to other locations. Prior to adding heat, an adulticide should be applied to
eliminate adult fly escapees.
Prevention is the most effective way to control fungus gnats. If adults can be prevented from
entering the growing rooms, then the problem is solved before it begins. Cracks in walls, and
around air conditioners, pipes and doors, are the usual routes of initial fly invasion. In one‐
zone systems, installation of fly netting over doors during spawn‐run has been helpful. In all
systems, limiting the amount of traffic into the room at anytime, can help reduce the likelihood
of infestation. Monitors can be used to determine the tightness of a room and the need for
doorway management. In general, if flies can be excluded through the time of casing, they will
have little or no direct impact. However, if there is disease on the farm, then the flies will vector
this into rooms at whatever time they enter.
Good sanitation is also important for fly control. Flies can breed in the stumpage and frag-
ments of discarded mushrooms, and spent compost may serve as breeding material. Spent
compost and mushroom stumpage should be removed from the premises. Growers should also
remove and dispose of trash promptly.
11 Insect, Mite, andNematode Pests ofCommercial MushroomProduction 225
The mushroom farm community must also be considered. Each room, block, and farm has
an endemic or background population of fungus gnats. These populations are specific for each
farm and will vary from crop to crop and season to season. Pest populations throughout the
farm community can only be brought under control if each grower understands the benefits of
a consistent and total fly control program. Cooperation among growers also promotes better
fly management, based on sharing of knowledge about fly biology and behavior, and the essen-
tial conditions that favor colonization and spread of disease pathogens.
18.104.22.168.3 Biological/biorational Control
Biological and biorational products are used to control sciarid flies. These manage specifically
the intended target, having little effect on humans, non‐target organisms, or the environment.
There are several larvicides available. Larvicides are most efficacious and efficacy is affected by
the life stage of the larva at application (Rinker, 2002). Bacillus thuringiensis var. israelensis and
diflubenzuron tend to be more effective against younger larvae, while entomopathogenic nem-
atodes, especially Steinernema feltiae, and methoprene are more effective against the older
larvae. Timing of application should rely on monitor counts. Application of benomyl may
reduce the effectiveness of the Steinernema feltiae (Atawa etal., 2013). Cyromazine and dif-
lubenzuron modify the development of the exoskeleton of the larva while azadirachtin and
methoprene, as insect growth regulators, mimic the naturally occurring hormones in the lar-
va’s body, interfering with the natural growth stages.
Timing a larvicide application based on monitoring the fly invasion will provide maximum
effectiveness. Larvicides must be applied when larvae are susceptible. This is especially true for
the insect growth regulator, methoprene. In order for this chemical to be effective, the fourth‐
instar larva must ingest it, making monitors and an appropriate system of record‐keeping
essential to time its application.
The location of the larval grazing area must be anticipated. Sciarid larvae tend to move up
into the casing from the compost or remain in the casing. Thus, a compost drench prior to cas-
ing is not efficacious for an invasion of flies after the casing is in place.
Various predatory mites, Stratiolaelaps (Hypoaspis) miles (Berlese), Geolaelaps (Hypoaspis)
aculeifer (Canestrini), and Stratiolaelaps scimitus (Womersley), have demonstrated success
against various sciarid species (Castilho etal., 2009).
Larval mortality by biological and biorational products is slower than the rapid organophos-
phates and the carbamates. Mortality is measured in days as opposed to minutes. Overall
effectiveness varies with the product and the timing. Cyromazine and diflubenzuron are more
efficacious than the predatory mites, nematodes, microbial pesticides, or insect growth
22.214.171.124.4 Chemical Control
Chemical insecticides typically target adults in production rooms, work areas, or surfaces
where the flies will rest, swarm, and roost. Growers should also treat walls, door jambs, and the
plastic cover that is placed over the compost after spawning. Adulticides in the form of aerosols
or dusts should be applied when the action threshold is reached.
Resistance to insecticides is a concern. Brewer etal. (1989a, b) in Pennsylvania (USA) and
Delaware (USA) have demonstrated resistance of this sciarid to permethrin and dichlorvos,
two widely used adulticides. Many insecticides commonly used in the mushroom industry are
metabolized by the enzyme system implicated in permethrin and dichlorvos resistance.
Adulticides should be used sparingly and alternately with other products of different mode of
action to extend the effectiveness of the product.
Edible and Medicinal Mushrooms
The use of chemical insecticides can be an important part of gnat control on a farm, but
growers should integrate their application with other practices.
11.1.2 Gall Midges, Cecids
Gall midges or cecid flies are small rarely seen flies. They are economic pests of agricultural
and food crops, forest trees, and ornamentals.
Cecid larvae (Figure 11.2) feed on the outside of the stipe or at the junction of the stipe and gills
of both Agaricus and Pleurotus species. Their presence can result in direct yield loss or in a loss
of quantity of fresh or processed marketable product.
Most of the literature has not attributed direct yield loss to a cecid infestation. However,
White (1990) demonstrated that yield loss can occur when as few as four larvae per square
meter are present during spawn‐run because of its reproduction potential (see Life History). By
mid‐cropping 3.5 million larvae per square meter have been observed (Wyatt, 1960).
The actual presence of the orange or white larvae on the stem and gills make the product
unmarketable. And, as the larvae migrate from the casing and across the mushroom tissue,
their presence induces moisture accumulation and they spread the bacteria that induce brown-
ing. Together, the quality loss is substantial.
Gall midges (family Cecidomyiidae) are small, rarely seen flies, about 1.5 mm in length. Several
species are associated with commercial mushroom production: Mycophila speyeri Barnes,
Heteropeza pygmaea Winnertz, and Mycophila barnesi Edwards (Chung and Snetsinger, 1965).
Midge larvae are white (Heteropeza spp.) or orange (Mycophila spp.); mature larvae are about
2mm in length. Adult Mycophila can be distinquished from Heteropeza adults by the former
have wing venation and the latter none.
Figure 11.2 Cecid larvae, orange cecid larvae on a mushroom.
Credit: Photo graciously provided by Oscar Lahmann. (See color
plate section for the color representation of this figure.)
11 Insect, Mite, andNematode Pests ofCommercial MushroomProduction 227
When populations are high, their larvae are readily noticed because they wander off the beds
and accumulate in heaps on the floor.
126.96.36.199 Life History
Gall midges in mushroom cultivation reproduce by a unique process called paedogenesis.
Cecids do not need to mature to the adult stage to reproduce. Instead, a mature (mother) larva
will give birth to 10 to 40 daughter larvae without becoming an adult and mating. This can
occur in a week or less. Thus, in a few weeks the number of larvae can multiply exponentially.
Developmental time is dependent on temperature with the optimum around 240°C. Chung
and Snetsinger (1965) observed non‐hybrid Agaricus brown strains producing twice as many
larvae as non‐hybrid whites.
Adult development may be triggered by environmental or nutrient stress suggest Chung
and Snetsinger (1968). These larvae feed for about 14 days, pupate, and produce adults in
18–21 days. At the time of primordia initiation, there are no mushrooms. So, larvae must
feed on mycelia in the casing and on the forming mushrooms. At maturity, the larvae con-
struct pupation chambers of mushroom compost and enter a one‐day prepupal stage. After
pupation, adults emerge and become active. Cecid development is strongly influenced by
temperature. At 7°C, the total generation time is 103 days. At a substrate temperature of
around 24°C during the spawn‐ and case‐run production periods, first‐generation flies can
emerge within 18 days. During later stages of production, when the substrate temperature is
allowed to drop to about 19–21°C, the developmental time per generation lengthens to
about 21 days.
188.8.131.52 Management Strategies
Gall midges are associated with infested casing material, especially peat. And, they disperse on
inadequately sterilized growing surfaces (trays, shelves, netting) and especially on tools, equip-
ment, and workers’ shoes and clothing. Any practice that minimizes fly dispersal contributes to
gall midge control.
184.108.40.206.1 Cultural Management
Practices similar to those employed for sciarid fly control should be implemented for cecid
220.127.116.11.2 Biocontrol/Biorational Control
There is little published research on the evaluation of any product against Cecidomyiidae of
commercial mushrooms. White and Czajkowska (2000) determined that there was a sublethal
effect of methoprene (in vitro) on both Mycophila and Heteropeza where larval fecundity was
reduced and paedogenic life cycle extended, suggesting that this might be helpful in cecid
Chemical management. Older literature suggested the use of diazinon or lindane to depress
the larval population growth (Hussey etal., 1960). White and Czajkowska (2000) determined
that there was a sublethal effect of permethrin (in vitro) on both Mycophila and Heteropeza
where larval fecundity was reduced and paedogenic life cycle extended, suggesting as with
methoprene that this might be helpful in cecid management.
11.1.3 Phorid Flies
Flies in this family of insects are world‐wide and are a pest of mushrooms in many countries.
They are commonly known as humpbacked flies or scuttle flies. Six species have been reported
Edible and Medicinal Mushrooms
from commercial mushroom facilities in the US (Robinson, 1977). The predominant species in
the recent literature is Megaselia halterata (Wood).
Megaselia halterata larvae feed at the growing hyphal tips of the mushroom mycelium. This
species, unlike Megaselia nigra and agarici that were pests in the 1940s in the United States,
does not consume the sporophores. Thus, direct yield loss correlates to the number of larvae
grazing on the mushroom mycelium. More than 12,000 females per square meter of produc-
tion surface are necessary before significant yield loss occurs (Rinker and Snetsinger, 1984),
which is 12 times more than the number required for Lycoriella ingenua (syn. Lycoriella mali)
(Kielbasa and Snetsinger, 1980). Although direct yield loss can be a problem, the greater threat
is the transmission of Lecanicillium fungicola (syn.Verticillium fungicola).
The eggs are about 0.2 by 0.5 mm and lack surface sculpture. Fertile eggs are translucent;
whereas, infertile ones are cloudy and opaque. The larvae lack an apparent head capsule and
possess posterior respiratory horns, thus differing from sciarid larvae (Figure 11.3); and the
first, second, and third instar larvae have cepahlo‐pharyngeal skeletons measuring 0.5, 0.8 and
1.14 mm, respectively. The pupae (puparia) are approximately 2 mm in length. Young pupae are
whitish with respiratory horns barely visible. Older pupae are yellow‐brown with fully devel-
oped horns. The outline of the adult fly is visible through the puparium near the time of eclo-
sion. The dark, proctal plates of the male can easily be seen as the pupae near eclosion. The
adults of both sexes are small, measure 2–3 mm, lack forked veins and cross veins in the wings,
and are easily recognized by their “humpbacked” appearance, laterally flattened hind femora,
and quick jerky movements.
18.104.22.168 Life History
Adult females are attracted to actively growing mycelium and oviposit near the hyphal tips. In
commercial operations, the mycelium is actively growing about four days after spawning and
after casing. Unspawned compost does not support reproduction. Adult females mate in 24 to
48 hours after eclosion, and have a two‐ to three‐day pre‐ovipositional period before laying
about 50 eggs unlike the sciarid fly, which starts oviposition within 6 hours of eclosion. The
average developmental time from egg to adult at 16 and 24°C is 51 and 37 days respectively,
with adults surviving 4–8 days.
Figure 11.3 Sciarid larvae with
distinctive black head capsule.
11 Insect, Mite, andNematode Pests ofCommercial MushroomProduction 229
Newly emerged and older adult phorid flies readily fly to a suddenly exposed light, especially
the shorter wavelengths of blacklight, blacklight blue, or cool white. Outside, flight activity is
restricted to the daylight hours. The larvae, pupae, and adults of M. halterata arefrequently
parasitized by an endoparasitic nematode, Howardula husseyi Richardson (Figure 11.4),
Hesling, and Riding (Tylenchida: Allantonematidae). Parasitism by this nematode does not
obviously change the external appearance nor appreciably affect the length of the fly life‐cycle;
its most significant effect is the reduction of fly fecundity. Laboratory fly populations can be
virtually annihilated within five generations by this parasite.
22.214.171.124 Management Strategies
The integrated pest management strategies for control of sciarid flies are effective in managing
Shorter wavelength lights than those used for sciarids are more effective for phorid flies. The
action threshold can be at least five times higher than that for sciarid flies.
126.96.36.199.2 Biological/Biorational Control
Neem‐based products along with other plant botanicals will suppress Megaselia populations
(Erler etal., 2009a,b). The juvenile hormone mimic, methoprene, may show some activity against
them (White, 1979). The microbial, Bacillus thuriengiensis var. israelensis has shown control
under field situations (Keil, 1991). The insect growth regulator, diflubenzuron (Scheepmaker
et al., 1997), and the entomopathogenic nematodes, Steinernema feltiae, and S. carpocapsae
(Navarro etal., 2014) do not control these phorids.
The natural parasitic nematode populations can be favored by not allowing compost
temperatures to exceed 27°C.
188.8.131.52.3 Cultural Practices
Since the phorid is smaller than the sciarid fly, the size of screening must be smaller to prevent
184.108.40.206.4 Chemical Control
Generally, phorids are more sensitive to the chemicals registered for sciarids. Since phorids are
attracted to the smell of the actively growing mycelium, adulticides should be applied about
Figure 11.4 Howardula husseyi, a
macerated female phorid fly showing
Howardula husseyi larve, gravid female,
Edible and Medicinal Mushrooms
four days after spawning and/or shortly after casing. Monitor counts will dictate the appropri-
ate timing of the influx of flies.
11.2 Mite Pests
Several groups of mites have been associated with mushroom cultivation. These include:
gamasids, pyemotids, tarsonemids, and tyroglyphids. The predominant group familiar to most
mushroom growers is the pyemotid or red pepper mites (Figure 11.5).
11.2.1 Pyemotid mites
Red pepper mites, al so known as pyemotid or pygmy mites, actually feed on molds (Trichoderma,
Monilia, and Humicola spp.). They seem to be found only on production of the commercial
button mushroom, where they may cause losses in marketable yield.
Red pepper mites do not cause direct damage to cultivated mushrooms, but their presence
often contributes to a loss in marketable yield. They are a nuisance to mushroom harvesters.
Importantly, their mere presence indicates other problems (Clift and Terras, 1995). Indirectly,
the mites vector diseases, especially Trichoderma aggressivum. These mites can carry the
Trichoderma spores in special areas under their legs (Keil, 1996). And, thus, they can contami-
nate uninfected areas with Trichoderma.
A number of species of pyemotid mites have been identified from mushroom farms (Wicht,
1970). These mites (family Pyemotidae) are tiny, 0.25 mm in length, and yellow‐brown.
220.127.116.11 Life History
The mites have a sexual adult stage and a generation time of 4–5 days. Adult females may lay
up to 160 eggs over a 5‐day period. They do not live on Agaricus mycelium but require other
Figure 11.5 Red pepper mites on the surface of mushrooms.
11 Insect, Mite, andNematode Pests ofCommercial MushroomProduction 231
molds for development. Thus, their presence alone suggests the presence of other molds, not
necessarily Trichoderma, in the compost.
18.104.22.168 Management Strategies
Proper compost preparation and its pasteurization will minimize weed molds and eliminate
the food source for red pepper mites, thereby eliminating red pepper mite populations. Red
pepper mites can survive pasteurization temperatures on compost drier than 68% (Clift and
Terras, 1995). The casing surface at the post‐crop heat treatment needs to be moist as well.
These mites tend to congregate on top of the carpophores and can be seen by shining a light
across the pre‐harvested mushrooms. They have the appearance of “red pepper” on the mush-
room surface, hence, the common name “red pepper mites.” This behavior enables dispersal by
flies or harvesters’ clothing. Water splash during the irrigation process moves mites to other
shelves and to the floor. Attention to fly management, common equipment moved between
production rooms, harvesters’ clothing and shoes, picking baskets, and sales containers (a.k.a.
punnets) is required to minimize spread of the mites and molds.
22.214.171.124 Chemical Management
Miticides are not registered for control. Some producers have found it “helpful” to reduce the
number of mites on the mushrooms for sales by first applying a registered fungicide to the
casing followed a few days later by a registered chemical insecticide drench.
11.2.2 Gamasid Mites
This group of mites is predatory. They will feed on other mites, fly eggs, and larvae and nema-
todes. In general, these mites can be recognized as a group because they are fast moving on the
compost or casing surface. Fletcher and Gaze (2008) note three species: Parasitus fimetorum,
Digamasellus fallax, and Arctoseius cetratus.
This mite group is an indicator of other crop situations. They will enter the crop attached to
flies. And, they will reproduce on other living things in the compost or casing. Since they move
about the substrate seeking a prey, they will spread other problems throughout the crop.
Control of this group is through the management of situations or conditions that permit their
entrance into the crop and survival.
11.2.3 Other Mites Associated withMushroom Cultivation
These mites include Tyrophagus spp., Caloglyphus spp., Histiostoma spp., and Linopodes
antennaepes (Fletcher and Gaze, 2008; Snetsinger, 1972). These mites do not feed on Agaricus
mycelium but other fungi present in the crop. Their presence indicates problems with poorly
made compost and/or inadequate pasteurization and conditioning.
The Tyrophagus spp. and Linopodes spp. have been associated with pitting and browning of
the stipe. However, this may be a secondary situation and not the primary cause for the bacte-
Control of this group is through the management of situations or conditions that permit their
entrance into the crop and survival.
11.3 Nematode Pests
Mushrooms nematodes can be grouped into at least two broad categories: beneficial and harm-
ful. Mushroom growers have typically thought of nematodes as being harmful to the crop.
Edible and Medicinal Mushrooms
Parasitic (mycophagous) and saprophytic nematodes are associated with commercial mush-
room yield loss. The occurrence of mycophagous nematodes in mushroom culture is rare
under modern mushroom farming techniques. Saprophytic nematodes are common. Generally,
their overall economic impact on production is minimal; however, under heavy populations
significant individual crop reduction is experienced.
Beneficial nematodes, on the other hand, control insect populations. They may be either
natural to the population or introduced to the mushroom crop to control mushroom pests.
11.3.1 Saprophytic Nematodes
There is inconsistency as to the correlation of nematode populations and mushroom yield
reductions. Nevertheless, all commercial mushroom operations attempt to minimize these
free‐living nematode populations.
126.96.36.199 Symptoms andSigns
In single‐zone systems black necrotic areas may be visible on the spawned compost surface
prior to laying of the casing. These spots may show some colonized compost but the mycelium
will be fragmented and the compost wet. These areas will not be re‐colonized by the mush-
room mycelium. The surrounding colonized compost will degenerate, and the nematodes will
migrate into the casing layer. With careful observation and a bright light, the nematodes can be
recognized as they flicker (reflecting the light) on the compost straws.
Often the casing is well colonized by the mycelium but after ruffling or scratching, the myce-
lium does not re‐knit well in spots or the whole shelf. Sometimes the casing will initially be
slow to be colonized by the mycelium. The mycelium is fragmented and the casing does not
hold together well. As a consequence, yield is reduced (Kaufman etal., 1984). Sometimes grow-
ers confuse the die‐back symptom of virus disease with nematode problems. As in the com-
post, the flickering nematodes may be observed on the casing surface with a bright light.
The whiteness of the mushroom may be negatively affected. Bacteria on which the nema-
todes feed reproduce well in the moist environment created by the nematodes. The nematodes
and their associated bacteria lower the quality of the fresh mushrooms (Grewal, 1991).
Sometimes brown fungal colonies develop on the compost or casing. This fungus,
Arthrobotrys spp., is a parasite of nematodes. Its presence is an indicator of high nematode
populations (Fletcher and Gaze, 2008).
188.8.131.52 Causal Agents
The majority of saprophytic nematodes recovered from mushroom casing samples belong to the
genera, Acrobeloides, Rhabditis, Choriorhabditis, and Caenorhabditis in the order Rhabditida.
They are all bacteria feeders, characterized by having three or six lips fused or replaced by other
structures. Their stoma lack a stylet and their cuticle is annulated or smooth. Amphids are
inconspicuous and the esophagus has a terminal bulb. The tail of the male usually possesses a
bursa supported by rays. There are no caudal glands.
184.108.40.206 Disease Cycle andEpidemiology
Saprophytic nematodes are common inhabitants of compost and casing mixtures. Under opti-
mum conditions, 50–100‐fold increase each week is possible. Under slow drying conditions,
especially during the pre‐pasteurization phase of compost, some nematodes can form resistant
stages which can enable them to survive pasteurization temperatures. Insects, equipment,
workers, and irrigation of the casing can disperse the nematodes. In older farms with wooden
ceilings, nematodes can reproduce in the wet insulation and drop onto the compost through
the condensation on the ceiling.
11 Insect, Mite, andNematode Pests ofCommercial MushroomProduction 233
220.127.116.11 Management Strategies
Good sanitation and hygiene practices reduce the spread of nematodes on the farm. Thorough
post‐crop pasteurization and cleaning of the production room, netting, and equipment will
reduce carry over from one crop to another. Farms with wooden shelving or trays need to do
an especially thorough post‐crop heat treatment since the nematodes may be located in crev-
ices of the wooden boards and survive the post‐crop heat treatment.
Maintenance of proper temperatures during pasteurization of compost is critical to reduce
the nematode threat. If the surface of the compost becomes dry during the pre‐pasteurization
phase, resistant stages of the nematodes may survive the pasteurization temperatures. Changes
in the length of the pre‐pasteurization period, air flows, and humidity control may be necessary.
Insects are excellent vectors of nematodes (Rinker and Bloom, 1983). A good integrated pest
management program is required to reduce this additional impact of flies on a mushroom crop.
The casing material can be a source of nematodes. Although peat may have different levels of
nematodes, generally, pre‐packaged peat is no problem in mushroom production if it is prop-
erly handled. Once opened, the peat should be mixed in a cleaned area with cleaned equipment
and used within 24 hours. However, if the bags become broken and the peat becomes wet,
nematodes will multiply. These bags should be discarded away from the farm.
Once nematodes are noticed on the compost or casing the best control is to reduce their
spread in the room and on the farm and to determine the source or cause of infestation. Tools
and equipment should be sanitized between shelves during the spawning operation. Ruffling or
scratching should be avoided where nematodes are visible on the casing. There are no regis-
tered chemical controls.
11.3.2 Parasitic Nematodes
Parasitic or mycophagous nematodes were serious pests of commercial mushroom production.
Extensive sampling of commercial mushroom facilities in Canada and the USA over the past 50
years has not revealed the presence of these nematodes. However, they remain problematic in
other regions of the world (Katyal etal., 2007). Hussey etal. (1969), and Goodey (1960) provide
good discussion of this group.
18.104.22.168 Causal Agents
Mycophagous nematodes are in several genera: Ditylenchus myceliophagus and Aphelenchoides
composticola. These nematodes have mouth parts that can penetrate the Agaricus mycelium
and feed exclusively on the mushroom mycelium, destroying it.
22.214.171.124 Symptoms andSigns
The symptoms and signs of mycophagous nematodes are similar to that of the saprophytic
ones. The fine strands of the mycelium are destroyed and the casing/compost becomes soggy
and smells with little or no production in the area.
126.96.36.199 Disease Cycle andEpidemiology
These mycophagous nematodes may be found in soil and peat. One female can produce up to
500 eggs. They can increase rapidly and reproduce as much as 25,000 times in one week.
As the food source disappears the nematodes group together in clumps or swarms. As with
the saprophytic ones, a light on the compost or casing surface will reveal their presence. This
behavior permits “easy” access to flies that can transport them to other locations. These nema-
todes can survive for six weeks without feeding and in a desiccated state for upwards of three
years. Poorly post‐crop heat treated spent compost could be a good source of these nematodes.
Edible and Medicinal Mushrooms
188.8.131.52 Management Strategies
These mycophagous nematodes may be found in soil and peat. Avoiding incorporation of soil
into compost, avoiding runoff from soil onto the compost or compost ingredients, or prepara-
tion on soil will minimize the risk from infection.
Maintaining adequate uniform phase II pasteurization temperature will assist in elimination
of this nematode. If the compost dries during warm‐up to pasteurization, then some nema-
todes may go into a resistant stage and infest the crop at spawning.
Once an infection site is identified, it is quite important to maintain vigilant control of flies.
Covering the infected area with plastic will minimize movement by personnel, insects, or irri-
gation. Adequate management of temperatures during post‐crop heat treatment, disposal of
the spent material away from the farm, a thorough cleaning of the room prior to reuse and a
heat treatment of the cleaned empty room before fresh substrate is added are critical.
No chemicals are registered for control although some literature suggests azadirachtin or
diflubenzuron (Gahukar, 2014) and the fungicides benomyl and thiabendiazole (McLeod and
Klair, 1978) may reduce population growth of Aphelenchoides.
11.3.3 Beneficial Nematodes
Beneficial nematodes are new to the thought processes of mushroom farmers. Beneficial nem-
atodes can kill the host directly, reduce its ability to produce offspring, or be a carrier of disease
to the insect. These nematodes fit well into biological control strategies for insects.
184.108.40.206 Endoparasitic Nematodes
The phorid fly (Megaselia halterata) has within this insect’s population a naturally occurring
nematode, Howardula husseyi. The nematode enters the fly larva and reproduces within the
fly. As the nematodes develop inside the fly, they consume the fly’s reproductive system. Thus,
an infected female produces few, if any, offspring. When she attempts to lay her eggs, the
nematodes are released back into the compost or casing, ready to infect other phorid larvae
(Figure 11.6). Commercialization of this nematode for biological control has not been
220.127.116.11 Entomopathogenic Nematodes
Another more successful commercial nematode product for mushroom fly control has been
the development of nematodes that enter the fly larva and release infective bacteria that kill the
Figure 11.6 Phorid larvae.
(See color plate section for
the color representation of
11 Insect, Mite, andNematode Pests ofCommercial MushroomProduction 235
fly larva. These nematodes either bore through the body of the insect or go through natural
openings in the insect larva. Once the infective‐nematode enters the fly larva, it releases bacte-
ria that it carries in its digestive system. As the fly larva dies the nematode uses the cadaver to
reproduce more young.
One of the more common nematode species for mushroom fly control is Steinernema feltiae.
It is one of most effective species against the sciarid fly, Lycoriella ingenua (syn. Lycoriella mali)
with 70% average control at the farm level. However, no entomopathogenic nematode species
has been reported to control the phorid fly. The nematodes are typically applied to the casing
material in the irrigation water with the timing of application important to maximize control.
These nematodes prefer to attack large fly larvae or young pupae, about 12–16 days from egg
laying. This necessitates appropriate monitoring of invading adult populations. The nematodes
may reduce the mycelial growth on the casing surface with a slightly weaker mycelial growth in
the casing at pinning time when commercially recommended rates are applied at casing time.
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