DISTRIBUTION OF GREEN MOULD ON INFECTED MUSHROOM FARMS and EFFICACY AND LIMITATIONS OF MUSHROOM GRAIN SPAWN TREATED WITH BENOMYL AGAINST GREEN MOULD DISEASE OF THE CULTIVATED MUSHROOM
DANNY LEE RINKERl, AL CASTLE2, GLEN ALMl and
l Horticultural Research Institute of Ontario,University of Guelph, Vineland Station, ON
LOR 2E0 CANADA; 2 Brock University, St. Catharines, ON L2S 3A1 CANADA
Background and objectives
Trichoderma harzianum Rifai, biotypeTh4, (green mould disease) has been a serious economic problem in the Ontario mushroom industry (Agaricus bisporus (Lange) lmbach) since 1992, having been confirmed on 2/3s of Ontario mushroom farms. The primary means of control is a thorough sanitation and hygiene programme'. Despite the noteworthy efforts by many farmers in reducing the occurrence of green mould on the farm, the means of its entry into seemingly "clean and well-protected areas" remained elusive. A project was initiated in the summer of 1996 to determine the probable means of green mould movement on infected farms.
Materials and methods
Air samples, debris and swabs of surfaces were taken from six mushroom farms with a green mould problem (five in Ontario and one in Alberta), with a total of nine intense samplings. Petri plates containing malt agar were placed in the open to collect fallout from the air. The cotton swabs or debris were placed directly into petri plates containing malt agar.
Two methods were used for identification of Trichoderma harzianum biotypeTh4. In the first method, the Th4 was identified by first purifying the mixed cultures and then growing the pure culture on malt agar in light. At the end of a four-day light exposure, the Trichoderma species was identified through classical taxonomical procedures and its growth characteristics on the media. In the second method, unpurified cultures were flooded with water and the spore suspension placed into small centrifuge tubes. This mixture was analysed using a PCR test highly specific for Th4 (and Th2) developed by the authors.
Results and conclusions
Trichoderma harzianum was recovered from several locations on infested farms. The incidence of green mould was greater inside than outside buildings.
Inside, the highest concentrations of green mould were the common areas where personnel cross paths, for example, lunch rooms, washrooms, time clocks, telephones, hallways and wall charts. Green mould was also isolated from the packing areas. Most importantly, green mould was also recovered from rooms that had been prepared for re-filling with the clean Phase 11 material. Outside, green mould mostly was isolated on spent compost and farm vehicle roadways.
Surfaces with the greatest amount of green mould were harvesting related equipment. Structural surfaces such as walls, floors, drains, windows, doors or telephones were contaminated with the green mould organism. Green mould organism was isolated from large equipment used to move Phase 11 or spawn run compost as well as from the clothing, shoes or hands of personnel.
Green mould spores were collected from the inside air only and these from only two of five farms where air was sampled. It appears that transfer of the Th4 through the air is uncommon.
The management of green mould disease is the implementation of information in an intelligent and integrated manner. The primary approach to Trichoderma harzianum, biotype Th4, management is sanitation and hygiene. The principal efforts should include personnel flow management, a thorough post-crop clean up, removal of spent compost from the farm and dust/debris management on roadways.