Mushroom Virus - Frustrating and costly
This Article was originally produced for the Australian Mushroom Journal Issue 4 2020.
Reviewing the factors that improve mushroom whiteness
For mushrooms, whiteness signals quality. It may also be assumed to indicate storage life, flavour and freshness. Presenting clean, white mushrooms to consumers is a proven way to increase sales. Conversely, browning on mushrooms is definitely a negative. Browning may be due to disease, bruising, dehydration or simply age and senescence.
Project MU19005 has reviewed the factors that improve mushroom whiteness, from the time compost and casing are prepared through to harvest and packing. The result is a combination of strategies growers can use right now, techniques that are close to commercialising and advances to watch into the future.
Dr Jenny Ekman will summarise the results from this review and discuss some of the “Best Bets” growers can use to improve mushroom whiteness.
Recycled organics as an alternative to peat in mushroom casing
The Australian mushroom industry uses approximately 25,000 tonnes of peat casing every year. Mostly imported from Europe or Canada at a cost of $300 per tonne, peat is both an expensive and limited resource.
Compost made from recycled organics is locally available and cheaper than peat.
Join Adam Goldwater from Applied Horticultural Research for a webinar where he will present the results of the recent trials of commercially viable white mushroom crops cased with blends of composted recycled organics and peat.
This is a Waste Less Recycle More initiative funded from the waste levy.
Getting the best from your cookout
As mushroom crops mature, pest and pathogen levels increase so that by the end of the crop, the pathogen population reaches its maximum (Fletcher & Gaze 2008). Effective crop termination is essential to reduce the pathogen population, allowing the next crop to ‘start clean’ and to break the cycle of diseases, such as Dry Bubble, which are perpetuated by continual on-farm re-infection.
By far the most effective termination procedure is cookout in situ, where the crop is treated undisturbed in the grow room with steam. An effective cookout prevents contamination of subsequent and adjacent crops which occurs when spent substrate contaminated with viable pathogens, pests and their larvae is removed from a grow room (Beyer 2018).
Cookout must kill pests and pathogens within the compost and netting on shelf farms and within the compost and tray timbers on tray farms. Cookout must also kill Agaricus mycelium and spores within the compost and tray timbers to prevent spread of virus diseases.
Cladobotryum spp. – Cobweb disease
Cobweb is the common name given to a fungal disease affecting Agaricus bisporus crops in mushroom growing regions worldwide.
It is caused by species of the genus Cladobotryum (formerly Dactylium), primarily Cladobotryum mycophilum and Cladobotryum dendroides. The pathogen grows rapidly over the casing surface and colonizes mushrooms at all stages of development with a white aerial mycelium, causing a destructive soft rot. Cladobotryum sporulates heavily and the spores are easily spread around the farm causing secondary infections. Spores landing on mushroom caps incite browning, causing loss of quality.
Until the early 1990s, cobweb outbreaks had little impact and were easily controlled by available fungicides and routine hygiene practices. But during the early 1990s, the incidence and severity of cobweb on British mushroom farms increased and in 1994/95 the disease reached epidemic proportions, regularly causing up to 40% crop loss.
Nematodes: A fly-in-fly-out pest of mushrooms crops
Long distance dispersal of nematodes occurs by a process called ‘phoresy’, the transport of a small animal by a larger animal.
In mushroom grow rooms, nematodes attach to Sciarid flies and are transported to fresh mushroom beds to establish new colonies and new infections.
This is further evidence demonstrating why effective fly control is highly significant in successful management of mushroom diseases and pests.
This article was originally produced for the Australian Mushrooms Journal 2020 Issue 1
Penicillium hermansii – Smoky mould
Smoky mould is a destructive compost infection first recognized in the Netherlands nearly 30 years ago. Despite being identified as various Penicillium species over the years, the true identity of the causal organism has only recently been confirmed through molecular analysis as Penicillium hermansii.
Penicillium species produce long chains of very small, lightweight, dry spores which are around 0.002mm in diameter (Fig. 1) and become airborne very easily. A single Penicillium colony (Fig. 2) will produce 400,000,000 spores per day. Although P. hermansii is very slow growing, it is problematic because of the large number of spores it produces and its short generation time. Penicillium hermansii will sporulate only three or four days after infection, producing thousands of daughter colonies which in turn sporulate rapidly.
Action points to control Sciarid & Phorid flies
Flies are effective vectors of disease because the sticky disease spores attach themselves to the flies legs and the flies transport them from crop to crop.
Sciarid and phorid flies can breed in bushland, ‘waste’ or ‘spent’ compost in the farm environment and, most efficiently of all, in growing rooms.
The odour associated with the Phase 3 compost arriving on a farm either in bulk or blocks acts like a strong magnet to attract flies to the new crop.
The fact that a female sciarid can produce around 100 offspring and a female phorid can produce around 50 offspring means that new crops need to be strongly protected from invasion by adults and a holistic and integrated approach to fly control is needed.
Sampling Methods for Mushroom Pest and Disease Testing
This video describes how to collect samples for disease testing using molecular testing techniques.
This video was produced as part of the pest and disease management and research services (MU16003) project.
It was funded by Hort Innovation using the Mushroom Industry research and development levy and contributions from the Australian Government.
Fact sheet: Syzygites megalocarpus – Troll doll
Troll doll is caused by Syzygites megalocarpus a Zygomycete which is ubiquitous in nature, colonizing a diverse variety of dead or moribund fleshy mushrooms. Syzygites (pronounced “size‐a‐guy‐tees”) was initially observed on cultivated mushrooms between 2004 and 2007 in crops of Agaricus blazei (Sun mushroom) in Brazil.
It was first recorded in Pennsylvania in August 2011 and has since become widespread on commercial beds throughout North America.
Confined initially to late flushes of brown portobello strains of Agaricus bisporus, Syzygites has since been observed on earlier flushes and on white strains of Agaricus bisporus. Due to the mould’s tolerance to low temperatures, it has also been observed in postharvest packaged product, the mould appearing while on the store shelf.