PG Suspension – Production at Forest Research

PG Suspension is a biological control agent for Heterobasidion annosum, (formerly known as Fomes annosus), which causes conifer root and butt rot.

PG Suspension is manufactured at Forest Research’s Alice Holt Lodge research station in Surrey. An average of three batches are produced each year to supply Forestry England's East Anglia Forest District. 

The product is a suspension concentrate comprising live spores (oidia) and mycelium of P. gigantea. The formulation contains a mix of spores, water, sugars and colour additives.

The PG Suspension mixture is pumped into sterile plastic tubing and sealed at intervals to produce small sachets which contain 7-10ml of product. If kept refrigerated the product will retain its viability for six months because the low water activity (aw) of the formulation ensures that the growth of most bacteria and yeasts is prevented.

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  P. gigantea mycelium is scraped off Malt agar plates
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  Spores are mixed with sugar water and honey
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  The solution is pumped through plastic tubing
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  Completed sachets

Each sachet must contain several million spores per millilitre of concentrated product in order to be successful. The concentration of viable spores is monitored before the product is dispatched to the field, and another mid-term test on viability is carried out in the laboratory to ensure the product has not deteriorated over time.

Related materials

• Conifer root and butt rot (Heterobasidion annosum) resources page