The fungus Phlebiopsi s gigantea has been used in Europe as a biological agent for the control of conifer root and butt (caused by Heterobasidion annosum) for nearly 40 years. P. gigantea competes with H. annosum for the woody resource within conifer stumps, and is applied to stump surfaces at felling. Three distinct biological control products based on P. gigantea have been developed: PG Suspension in the UK, PG IBL in Poland and Rotstop in Finland. The formulations are of oidia, which are maintained in a sucrose suspension, sawdust, or a wettable powder, respectively. PG Suspension and PG IBL are applied to pine stumps, while Rotstop is equally as eVective on pine as on Norway spruce stumps. For each product, isolates of P. gigantea are selected from the wild and are screened for their competitive ability against H. annosum before formulation. Viability and purity checks are undertaken throughou t the production cycle and during routine use. The increasing use of mechanized harvesting machines to fell and process trees is having an impact on this biologica l control system, the formulations having to be compatible with the mechanical applicatio n systems and vice versa. This paper compares the formulation, testing and applicatio n of the three products, and considers some aspects of their future development.
The longevity of Fomes annosus in conifer stumps was assessed in 3 investigations, which showed that the fungus could remain active in stumps for periods of 16 to 62 years.The important role of the stump in the biology of Fomes annosus was clearly demonstrated by RiSHiiiiTH (1950RiSHiiiiTH ( , 1951. During 3 recent investigations we have obtained information on the longevity of F. annosus in eonifer stumps, whieh has an important bearing on the danger of infeetion in subsequent conifer crops.1. In 24, second-rotation Sitka spruce {Picea sitchensis [Bong.] Carr.) crops, affected to varying degrees by F. annosus butt-rot, three-metre-square plots were laid down at random through the study areas, and were cleared of brash and surface litter. Stumps remaining from the previous crops were carefully examined. The species, size and the presence or absence of active F. annosus were recorded for each stump. Fomes annosus was considered active if fresh sporophores were found on the stump, or if decayed wood in the stump contained fresh white pockets. The approximate ages of the stumps were calculated from the dates of clear-felling, which were obtained from records of forest operations. Some of the stumps examined may have been from earlier thinnings, and could therefore be older.Of the 24 crops, 21 had previous crops of Scots pine {Pinus sylvestris L.) or European larch {Larix decidua Miller), pure or in mixture. Active F. annosus was found in pine stumps from 33 to 62 years of age, on four sites. The 62 year-old pine stumps were small, 200-300 mm in diameter, and most of them had almost totally disintegrated. Infected larch stumps from 30 to 46 years of age were found on seven sites. Thirtyyear-old Douglas fir {Pseudotsuga menziesii [Mirb.] Franco) stumps on two sites were infected, and single sites of Norway spruce {Picea abies [L.] Karst.) (33-year-old) and Sitka spruce (30-year-old) had infected stumps. The sites were scattered throughout Britain, and were mainly on freely-drained brown-earths with an average pH of about 4.5. Ages of the previous erops at felling ranged from 12 (one of the Douglas fir sites) to about 80 years.2. In Kerry Forest, North Wales, the stumps of 30-year-old Sitka spruce felled in 1959 were examined. The crop was the second or third conifer rotation and was unthinned at clear-felling, when it was estimated that 80 "/o of the trees were infected Eur.
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