Location of immature stages of the mushroom insect pest Megaselia halterata in mushroom-growing medium

Experiments were conducted to examine the location of oviposition by the phorid fly Megaselia halterata (Wood) (Diptera: Phoridae) in uncased and cased compost. Clearly, a majority of the gravid females choose oviposition sites directly after entering the top layer of the compost. In uncased compost, 60% of all adults emerged from the top of four compost layers of equal thickness. When the compost was covered by a casing layer which was still uncolonized by Agaricus bisporus, oviposition was further concentrated in the top compost layer. In this situation, 91% of all adults emerged from the top compost layer whereas only 1.5% emerged from the casing. When the casing layer was colonized by mushroom mycelium, 45% of all adults emerged from the casing layer and 53% emerged from the top compost layer. Further concentration in the top compost layer and the casing layer occurred as a result of upward migration of larvae. When compost was cased after oviposition, up to 43% of all adults emerged from the casing layer. We concluded that in the control of phorid infestations with insect pathogenic nematodes, applications in uncased compost can be restricted to the upper compost layer. When compost and casing are filled simultaneously, nematode applications in the casing layer only could be considered.     

Influences of compost and casing layer depths on the mechanical properties of mushrooms

The mushroom growing bed consists of an underlying compost which is covered with casing (a peat and chalk or lime mixture) to induce fruit-body formation. The influences of the depths of the compost and casing layers on the mushroom texture, susceptibility to bruising, and ease of detachment from the growing bed surface were investigated. Textural properties were determined on cubes of cap tissue and detachment torque was determined by using an instrumented rotating suction cup which was lowered on to the caps. The proportion of mushrooms which detached at the base from the bed surface was recorded, since this is an important parameter for an automatic (robotic) harvesting system. Shallow casing resulted in mushrooms that were firmer and less likely to deform plastically, but that showed greater discolouration after a standard bruising treatment. Shallower casing also increased the proportion of mushrooms that detached at the base. Increasing the depth of compost produced firmer mushrooms, significantly increased the detachment torque and reduced the proportion of mushrooms detached at the base. The proportion of mushrooms that detached at the base correlated negatively with the plastic deformation of cap tissue. A positive correlation was found between mushroom dry matter content and tissue firmness.     

Pseudomonas tolaasi in Mushroom Crops: A Note on Primary and Secondary Sources of the Bacterium on a Commercial Farm in England

Primary sources of Pseudomonas tolaasi Paine on a mushroom farm were the peat and limestone used in the casing process. The pathogen could not be detected in the farm soil, water supply, the mushroom spawn used, or in compost after spawning, but was isolated from the casing (peat/limestone mixture) layer of symptom-free mushroom beds and both the casing layer and compost of beds bearing diseased mushrooms. Secondary sources were numerous once the pathogen was present in mushroom beds. These included symptomless and diseased mushrooms, the fingers and shoes of people handling the crop, their baskets, knives and ladders. Ps. tolaasi could be isolated from dust in the air in infected houses and also from floors. Spores of infected mushrooms may transport the bacterium, as did sciarid flies and mites which are common pests of mushroom crops.     

Temperature,time, and the influence of volatiles on phialospore germination in Verticillium malthousei Ware

Phialospores of Verticillium malthousei Ware were atomized onto acclimatized water agar and incubated for 3, 6, 9, 12, and 24 hr at 12 to 36 °C at 6 °C intervals. Germination occurred at all temperatures exclusive of 36 °C with maximum germination (90–98 %) occurring in 24 hr at 12 °C, 12 hr at 18 °C, 9 hr at 24° and 30 °C. Volatiles from: 1) horse manure compost colonized by Agaricus bisporus; 2) mycelium impregnated casing (soil); or 3) casing supporting mature and immature mushrooms had no statistically significant effect on spore germination of V. malthousei when measured after 12 hr at 24 °C. However, a tendency towards inhibition after 6 and 12 hr at 24° and 12 °C, respectively, suggests the inhibition is temperature and time dependent. This dependency was noted with two substrates, colonized compost and casing which supported sporocarps.The statistical and programming assistance of Dr. J. A. Ayers, Department of Plant Pathology, Dr. R. Craig, Department of Horticulture, and Ms. Isabel M. Hoover, Agricultural Statistic Laboratory, The Pennsylvania State University is gratefully acknowledged.Contribution No. 759 from the Department of Plant Pathology, The Pennsylvania Agriculture Experiment Station. Authorized for publication as Journal Series Paper No. 455.0 on October 8, 1973.     

Re-supplementing and re-casing mushroom (<Emphasis Type="Italic">Agaricus bisporus</Emphasis>) compost for a second crop

Experiments were performed to determine the effect of adding nutrient supplements to colonized mushroom compost (MC) for the production of a second crop of mushrooms. Mushrooms were harvested for 1, 2 or 3 flushes, the casing removed and the MC then was fragmented and re-supplemented with delayed release supplements treated or non-treated with fungicide (thiophanate-methyl; Topsin M 70WP) and re-cased. Overall double-crop yields were higher when MC was re-supplemented after 1st flush (1st flush MC) as compared to re-supplementation after the 2nd or 3rd flushes. Mean double-crop BEs were 128, 119 and 109% when 1st-, 2nd- and 3rd-flush MCs were used, respectively. Treatment of delayed release supplement with thiophanate-methyl fungicide did not affect mushroom yields. Soluble salts and potassium concentrations increased 350 and 900%, respectively, in the casing overlay through three flushes suggesting that removal of the casing would help to alleviate the build up of these potential growth-limiting materials. Re-supplementing and re-casing of MC represents a potential opportunity for growers to increase revenues and reduce costs associated with preparation and disposal of compost. The ability to double-crop mushroom compost would provide growers a chance to increase yields by 40% or more, depending on whether they re-supplement and re-case after 1st, 2nd or 3rd flush.     

Scanning Electron Microscope Studies of Interactions between Agaricus bisporus (Lang) Sing Hyphae and Bacteria in Casing Soil

Relationships between the hyphae of Agaricus bisporus (Lang) Sing and bacteria from the mushroom bed casing layer were examined with a scanning electron microscope. Hyphae growing in the casing layer differed morphologically from compost-grown hyphae. Whereas the compost contained thin single hyphae surrounded by calcium oxalate crystals, the casing layer contained mainly wide hyphae or mycelial strands without crystals. The bacterial population in the hyphal environment consisted of several types, some attached to the hyphae with filamentlike structures. This attachment may be important in stimulation of pinhead initiation.     

Effects of Caenorhabditis elegans (Nematoda: Rhabditidae) on yield and quality of the cultivated mushroom Agaricus bisporus

Thirteen species of saprobic rhabditid nematodes (11 genera) were identified from samples of compost and casing material collected from mushroom farms in the British Isles. Caenorhabditis elegans, the most frequently found saprobe, was mass-produced monoxenically and its effects on the cultivated mushroom, Agaricus bisporus (strain U3) were studied. C. elegans did not multiply in well-prepared, pasteurised, spawned compost, whereas casing material proved to be a highly suitable environment for its reproduction. An initial casing inoculum of 10⁶ nematodes/crate of compost (7.5 kg), caused a significant reduction in mushroom yield. Losses in total mushroom yields of 11%, 20% and 26% were caused by initial inoculum rates of 10⁶, 10⁷and 2 × 10⁷ nematodes/crate, respectively. Yields were negatively correlated with the initial nematode inoculation level and regression equations were derived. The nematode treatments caused fewer mushrooms to be produced and an absence of the usual distinctive flushing patterns. C. elegans caused considerable deterioration in mushroom quality and characteristic distortion of mushrooms. Individual sporophores were mis-shapen, notched and had brown or violet coloured grills. Up to 3.8%, 6.7% and 10.8% of total weight and 3.5%, 5.4% and 8% of total numbers of mushrooms were distorted at the three highest nematode inoculum rates tested. Weights and numbers of distorted mushrooms were positively correlated with the initial nematode population. C. elegans commonly colonised sporophores.     

The control of paedogenetic cecid larvae in mushroom beds by the use of thionazin

Thionazin incorporated in the casing layer of mushroom beds was shown to be highly phytotoxic even at 5 ppm, but when incorporated in compost it caused little phytotoxicity up to 20 ppm. A rate of 8 ppm gave satisfactory control of Heteropeza pygmaea Winnertz (Dipt.: Cecidomyiidae), but was less suitable against Mycophila speyeri (Barnes), for which the use of γ-BHC in the casing should be retained. A severe infestation of M. speyeri was shown to depress the total yield of mushrooms by 59% and the saleable yield by 87%.     

Garbage Composting for Mushroom Production

Laboratory and pilot-plant composting of garbage mixtures of newspaper and vegetable waste has demonstrated that garbage can be converted to a medium that produces mushrooms (Agaricus campestris) in good yield. Sewage sludge was less satisfactory than newspaper, gumwood sawdust, or vegetable waste as a compost material for growing mushrooms. A sample of commercially produced compost was found to yield mushrooms in the same quantity as was produced in the laboratory experiments.     

Physiologic response of Agaricus subrufescens using different casing materials and practices applied in the cultivation of Agaricus bisporus

Casing materials and practices used in the cultivation of Agaricus bisporus were evaluated in the cultivation of Agaricus subrufescens, using the best techniques for optimization of production, including the possibility of re-casing of the compost for the production of a second crop of mushroom. Casing based on peat moss, loam soil or coir was compared to casing material mixed with or without spawn-run compost. Based on the results, we conclude that the casing layer used in the cultivation of A. subrufescens should not necessarily be the same as that used in the cultivation of A. bisporus. For the tested strain cultivated with loam soil as casing layer, the ruffling technique is highly superior to CACing and should be pursued in further research. The re-casing of compost in new cycles showed good results suggesting that the currently used compost could be improved.     

Physiological studies of a hybrid between populations of Dactylis glomerata from contrasting climatic regions. II. Intra population variation

Mushroom compost was treated with nematicides and infested with Aphelenchoides composticola at the time of filling into growing containers. Yields of mushrooms from infested untreated control composts were reduced to 40–60% of yields from uninfested control compost. Yields from infested compost treated with fenamiphos emulsifiable concentrate (e.c.) at 10 or 20 mg a.i./kg, thiabendazole wettable powder at 40 or 60 mg a.i./kg or oxamyl granules at 20 mg a.i./kg were as high as from uninfested controls. Compost treated with granules of AC 64,475 up to 20 mg a.i./kg or ethoprophos or thionazin up to 80 mg a.i./kg gave yields significantly lower than uninfested controls. Numbers of nematodes rose to about 10⁶/20 g of compost in untreated compost and then fell, and a similar peak occurred in treatments in which yields were substantially reduced by nematode damage. Treatments which yielded as well as the uninfested controls held maximum nematode numbers down to about 10V20 g of compost but populations stayed at this level or tended to rise while numbers in untreated compost fell. Incorporation of fenamiphos in casing or its application to the surface of beds 3 wk after cropping began gave lower yields than the uninfested control but mushrooms were being produced late in the cropping cycle. Fenamiphos e.c. at 20 mg ai./kg incorporated in compost is considered a practical preventive measure for control of A. composticola.     

Comparative Assessment of biological (Nematoda: Steinernema feltiae) and chemical methods of control for the mushroom fly Lycoriella auripila (Diptera: Sciaridae)

The sciarid fly Lycoriella auripila is the major pest of mushrooms cultivated in the UK. Its larvae, which are capable of damaging the crop at all stages of production, may cause severe yield losses and can only be controlled with chemical pesticides. An indigenous isolate of the insect‐parasitic nematode Steinemema feltiae was tested as a biological control agent and its effects compared with two commonly used insecticides, diazinon and diflubenzuron. The timing of application of nematodes was found to affect their efficacy. When applied to compost during spawning, nematodes did not significantly reduce fly emergence, but they did if applied at casing when they were almost as effective as diflubenzuron. Diazinon incorporated into compost did not reduce fly emergence and was also the only treatment that did not lower the incidence of mushrooms spoiled by tunnelling of the larvae of L. auripila. When compared with untreated control plots those treated both with diazinon and diflubenzuron showed significant mean losses in yield of 10% in total weight and 17% in total numbers of mushrooms picked. In contrast, when S. feltiae was applied at casing significant mean increases in yield of 7% and 19%, respectively, were attained. Infective nematodes persisted well in casing, very few were found on sporophores.     

Performance of olive mill solid waste as a constituent of the substrate in commercial cultivation of Agaricus bisporus

The feasibility of using olive mill waste (OMW) as an ingredient in the substrate used for cultivation of Agaricus bisporus (Lange) Sing. was studied in a large-scale cultivation trial, concerning 2500 m² of mushroom growing area, at a specialized mushroom farm. Standard commercial cultivation technique involving compost preparation, spawning, casing and harvesting was used. The performance indicators such as mushroom yield, biological efficiency, market quality as well as horticultural value of the spent compost showed that the compost prepared with OMW was superior to the control compost in all the categories. The OMW-amended substrate supported higher populations of beneficial microorganisms especially, actinomycetes which enabled the breakdown of the compost ingredients. It is suggested that OMW is a suitable ingredient for the preparation of mushroom substrate. We have demonstrated that conversion of OMW (a liability) into value-added mushroom substrate (an asset) is an effective waste management tool in oleaculture.     

Effects of Application Rates of Steinernema feltiae (Nematoda: Steinernematidae) on Biological Control of the Mushroom Fly Lycoriella auripila (Diptera: Sciaridae)

The potential of Steinernema feltiae for the biological control of Lycoriella auripila was tested in commercial mushroom‐growing conditions. The nematodes, applied at rates of 1.5, 3, 6 or 12 x 10 ⁶ infective juveniles per 34 kg tray of spawn‐run compost, were mixed into the casing material before it was spread over the compost surface. When compared with untreated control trays, any rate of nematode application significantly reduced fly emergence. Insecticides significantly reduced mushroom yields; nematodes significantly increased them. At a rate of 3 x 10 ⁶ infectives/tray S. feltiae elicited mean total increases in the weight and numbers of mushrooms produced of 8% and 11% respectively. The nematodes also reduced the incidence of mushrooms spoiled by tunnelling sciarid larvae. The early decline in the numbers of nematodes persisting in casing was a trend that was reversed later, when evidence was obtained that S. feltiae was recycling in insects that had been killed. When applied at a rate of 3 ‐10⁶infectives/tray of compost S. feltiae should provide reliable and cost‐effective biological control of L. auripila.     

Improvement of yield of Pleurotus eryngii var. eryngii by substrate supplementation and use of a casing overlay

Improved yield and biological efficiency (BE) of Pleurotus eryngii var. eryngii were achieved by supplementation of substrate with a commercial delayed-release nutrient and use of a casing overlay. Yield increases of 14% were achieved from cased substrates that were supplemented at time of casing with delayed-release nutrient (Remo’s). Use of a casing layer enhanced yield by 141% over non-cased substrates. When casing and substrate supplementation were combined, yield increased 179% over non-cased/non-supplemented substrates. Mushrooms harvested from cased substrates were darker in color and solids contents were lower compared to non-cased substrates. An additional break of mushrooms was harvested from non-cased “spent” substrate by fragmenting and re-supplementing the substrate prior to the application of a casing overlay. Three production methods were compared for their effect on mushroom yield: “standard”, “casing” and “casing after first break”. Casing of the substrate before first break (“casing” production method) resulted in the highest yield and biological efficiency.     

Holistic assessment of the microbiome dynamics in the substrates used for commercial champignon (Agaricus bisporus) cultivation

Microorganisms strongly influence and are required to generate the selective substrate that provides nutrients and support for fungal growth, and ultimately to induce mushroom fructification under controlled environmental conditions. In this work, the fungal and bacterial microbiota living in the different substrates employed in a commercial crop (compost phase I, II and III, flush 1 and 2, and casing material on day 1, 6 and 8 after compost casing and during flush 1 and 2) have been characterized along the different stages of cultivation by metataxonomic analysis (16S rRNA and ITS2), analysis of phospholipid fatty acid content (PLFAs) and RT-qPCR. Additionally, laccase activity and the content of lignin and complex carbohydrates in compost and casing have been quantified. The bacterial diversity in compost and casing increased throughout the crop cycle boosted by the connection of both substrates. As reflected by the PLFAs, the total living bacterial biomass appears to be negatively correlated with the mycelium of the crop. Agaricus bisporus was the dominant fungal species in colonized substrates, displacing the pre-eminent Ascomycota, accompanied by a sustained increase in laccase activity, which is considered to be a major product of protein synthesis during the mycelial growth of champignon. From phase II onwards, the metabolic machinery of the fungal crop degrades lignin and carbohydrates in compost, while these components are hardly degraded in casing, which reflects the minor role of the casing for nourishing the crop. The techniques employed in this study provide a holistic and detailed characterization of the changing microbial composition in commercial champignon substrates. The knowledge generated will contribute to improve compost formulations (selection of base materials) and accelerate compost production, for instance, through biotechnological interventions in the form of tailored biostimulants and to design environmentally sustainable bio-based casing materials.     

Formulating Atoxigenic Aspergillus flavus for Field Release

A procedure was developed to encapsulate mycelia of an atoxigenic strain of Aspergillus flavus in alginate pellets for seeding into agricultural fields in order to reduce aflatoxin contamination via competitive exclusion. Kaolin, a clay filler commonly employed in alginate formulations, was detrimental to pellet performance as measured by spore yield. Corn cob grits, a by-product of the corn industry, was found to be an excellent replacement for kaolin. Of nine nutritive adjuvants tested, wheat gluten improved pellet performance the most, although gluten concentrations above 5% were difficult to process. The best formulation tested consisted of 1% sodium alginate, 5% corn cob grits and 5% wheat gluten. On a 'per gram' basis, this alginate formulation yielded more spores than either A. flavus sclerotia or colonized wheat seed. Pesticides were also tested as adjuvants with potential use for protecting pellets under field conditions. Only one (chloramphenicol) of four tested pesticides (the others were dichloran, rose Bengal and cyfluthrin) reduced pellet sporulation. Formulations with or without pesticide adjuvants retained similar spore yield potential during a 2-year storage at 8 C. However, spore production in stored products lagged behind that of fresh products. At 75% relative humidity (RH), pellet storage stability decreased with increasing temperature from 27 to 42 C. Pellet spore yield at 32 C decreased as RH decreased from 100 to 90%. Sporulation occurred at 90% RH but not at 88% RH. Spore yield varied widely in four field tests, and the cumulative spore yield was inversely correlated (r2= -0.798, P 0.01) with rainfall. The results suggest that alginate pellets may be effective formulations for delivery of atoxigenic A. flavus strains to furrow-irrigated cotton in desert environments, where aflatoxin contamination of cottonseed is most severe.     

Effects of bendiocarb and diflubenzuron on mushroom cropping

When mixed into the casing or compost layers of a mushroom bed in the absence of pests, bendiocarb decreased yield and number of mushrooms according to concentration. The most severe effects were on mushroom number at the two highest rates used (100 and 1000 μg/g), and there were large increases in mushroom size. Effects of bendiocarb incorporation in the compost diminished with time, and there was partial compensation in yield and numbers at the fourth flush. The action of bendiocarb persisted when it was mixed into the casing. Diflubenzuron showed some opposite effects at lower concentrations. When either mixed into, or drenched onto the casing at the commercial rate (30 μg/g), yield and size were both increased and the timing of the flushes was unaffected. At the two higher concentrations (180 and 1080 μg/g), reductions in yield and number and an increase in mushroom size were shown. However, these effects became more severe with time, especially those on mushroom number, possibly due to the accumulation of a toxic breakdown product.     

Inoculation of Scytalidium thermophilum in Button Mushroom Compost and Its Effect on Yield

Scytalidium thermophilum isolates in culture, as well as the endogenous strain(s) in mushroom compost, were inactivated at 70°C. This temperature was used to pasteurize composts for experiments. Of nine thermophilic fungal species, only S. thermophilum and Myriococcum thermophilum grew well on pasteurized compost in test tubes. The effect of both species on the crop yield of Agaricus bisporus mushrooms was studied. In solid-state fermentation rooms called tunnels, compost was pasteurized and inoculated. After incubation, the inoculated organisms were reisolated and counted, showing their successful colonization. The yield of mushrooms on inoculated composts was almost twice that on the pasteurized control. This result demonstrates the effectiveness of S. thermophilum in compost preparation. Inoculation is not necessary for traditional compost preparation. Naturally occurring strains of S. thermophilum, present in ingredients, readily colonize compost during preparation. Inoculation may be vital if compost is pretreated at a high temperature in tunnels. This finding is of relevance for the environmentally controlled production of high-yielding compost.     

Substrate dependent larval development and emergence of the mushroom pests Lycoriella auripila and Megaselia halterata

Pasteurized, spawned, full-grown and immediately-cased full-grown compost were simultaneously exposed to natural populations of the mushroom pests Lycoriella auripila (Winnertz) (Diptera: Sciaridae) and Megaselia halterata (Wood) (Diptera: Phoridae). Different numbers of adults emerged from each of these composts. Highest numbers of L. auripila emerged from spawned and pasteurized compost whereas lowest numbers of L. auripila emerged from full-grown compost. the emergence from full-grown compost was delayed, which could be explained by the delayed development of the larvae in this type of compost. High numbers of M. halterata emerged from compost that was completely colonized by the mycelia of the edible white button mushroom Agaricus bisporus (Lange) Imbach. The immediate covering of the compost with a casing layer significantly lowered the numbers of emerging M. halterata flies. Compared with the emergence pattern from full-grown and immediately-cased full-grown compost, adult M. halterata showed a delayed pattern of emergence in spawned compost. Adult M. halterata did not emerge from pasteurized compost. The results of these experiments enabled us to improve the timing of the application of insect pathogenic nematodes in the control of the larvae of both insect pests.