Inoculation
Inoculation is the introduction of the live fungus into the log. Shiitake spawn should be introduced into logs no sooner than 2 to 3 weeks after felling. If it. Is introduced earlier, the spawn probably will not survive. This ageing period after felling allows time for the tree cells to die before inoculation. Because the log is not sterile, it is important to introduce the spawn into many places spaced evenly along the log surface. An even, heavy inoculation density gives shiitake a competitive advantage over other micro-organisms. Introduction of soil or debris into the inoculation holes must be avoided.
Partially rotted logs should not be used. Logs cut in the fall through spring are inoculated in the spring, generally when mean daytime temperatures approach 10° to 16°C (50° to 60°F). Holes are drilled into the log in rows lengthwise to the log. Holes in each row are spaced roughly 20 to 40 cm (8 to 16 in.) apart; rows are 5 to 10 cm (2 to 4 in.) apart. To equalize inoculation density across the log surface, the holes in each new row are offset 10 to 20 cm (3 to 8 in.) from the last row (Fig. 2).
Usually, 10 to 30 pieces of spawn are required per log. Holes should be of a suitable diameter for a snug fit of the spawn plug—i.e., usually 1 to 1.5 cm (1/4 to 3/8 in.)—and of a depth that the spawn plug fits nearly flush with the log surface (Fig. 3). The depth of the hole may be easily standardized by attaching a locking sleeve to the drill bit which limits the depth that the bit will penetrate.
Spawn plugs are placed into the holes and gently pounded in with a hammer or mallet. A convenient method is to initially hold the spawn plug with forceps. If sawdust grown spawn is used, the holes should be completely filled with spawn. After inoculation, the surface of the log where the spawn was introduced is lightly painted with hot paraffin to seal in moisture and to disinfect the surface. Inoculation should be done in a shaded area to avoid direct exposure of the spawn to sunlight.
Author: Gary F. Leatham
The author is a Research Microbiologist, USDA Forest Serv., Forest Prod. Lab: P.O. Box 5130, Madison, WI 53705. The Laboratory is maintained in cooperation with the. Univ. of Wisconsin, Madison.
