10


PESTS AND DISEASES >


ble guest. By carrying out spore pressure measurement on delivery of compost from an infected tunnel, it is possible to identify the presence of Smokey Mould. At the moment the spawned compost is removed from the tunnel and filled into a growing room, infection with Smokey Mould can occur. After infection the Smokey Mould mycelium grows unseen and between the Agar- icus mycelium. Smokey Mould does however have a clearly shorter time to colonise the compost , while at the same time the temperature is lower during culti- vation and harvest so that Smokey Mould grows more slowly. But, because Smokey Mould keeps developing in the compost until the end of cultivation, the infection pressure on a farm can continue to mount up and form a threat for new growing rooms that have yet to be filled.


Cause Mild symptoms and occurrence only in a later flush could be attributed to infection of the incubated compost. However, with a sharp temperature rise im- mediately after filling the growing room with incubated compost and high losses in the first flush, it would be logical to assume that the mould was already present in the incubated compost and that the infection must have been present at the moment of inoculation. But where does the infection originate from? The true origin of Smokey Mould is still shrouded in mystery. As mentioned previously, Smokey Mould is caused by a new strain of mould (Penicillium her- mansii). This mould is unknown in other sectors and there are no additional isolates or other locations of substrates found in the CBS database (which contains more than 10,000 Penicillium isolates). Research shows that the spores and mycelium fragments of Smokey Mould are destroyed at relatively low temperatures (52 °C) and are unable to survive 60 °C in the pasteurisa- tion phase and certainly not the 80 °C reached during fermentation. As stated earlier, these experiments were performed in fluid mediums. Whether the results can be translated to practical situations where there are other influential factors (e.g. dry patches in the compost), still has to be investigated further. Another possibility is that Smokey Mould forms heat resistant ascospores that are able to survive difficult conditions. These have not been encountered until present.


[Figure X1. Smokey Mould (= Penicillium hermansii). A. Growth on nutrient medium. B. Growth on small particles of straw placed on nutrient medium malt extract agar (MEA). C. Close-up of colony on MEA. D. Microscopic image in which conidiophores of P. hermansii are visible. E. Conidia (= spores); occur in enormous amounts in the air after compost infected by Smokey Mould has been disturbed].


Control Small-scale trials have been run to investigate if and how Smokey Mould can be controlled. Bacillus subtilis is a natural bacterium that is used by some compost companies to control Trichoderma. This preparation was added to the compost at the moment of inoculation, but failed to perform; Smokey Mould developed as usual. At the time of inoculation, various concentrations of Sporgon were mixed through the compost. This visibly limited the growth of Smokey Mould mycelium and when applied in the highest concentration no Smokey Mould was visible at all. Further research must show which is the best method of treatment and which requi- rements apply for the admission of this fungicide.


Prevention and management Prevention is always better than cure, and this certainly applies in the case of Smokey Mould ‘disease’, which is impossible to cure. The tips below are based on our own research and on practical experience. Fermentation: Avoid dry patches, ensure the compost is well blended and homogenous so that all parts have the right moisture content and reach the right tempe- rature. Pasteurisation: The customary pasteurisation time of eight hours at 56 °C air temperature should be adequa- te. Here too ensure the compost is well moistened and that the ammonia content is high enough to eliminate harmful pathogens . Inoculation: Stringent hygiene measures at inoculation are always vital, and even more so if you are dealing with Smokey Mould. The incoming air must be filtered extremely well as this mould produces huge amounts of miniscule spores (< 2 micrometres) that are released into the air in large amounts. Cultivation: It is essential to cook out infected compost in the growing rooms (8 hours at 70 °C) to prevent huge clouds of spores spreading and germinating over the whole farm, as these spores can infect or re-infect other growing rooms. The immediate vicinity of a growing room that is being filled must be clean. Growing at lower temperatures can delay the growth of Smokey Mould and reduce the problem. Wet compost will exacerbate the problem, in drier compost the ex- tent of infection can be contained to some degree. ◗


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44