Steam sterilisation of mushroom tunnels
There are clear environmental benefits from developing systems that reduce chemical usage within the industry without incurring excessive extra costs.
This hygiene control system may contribute to pesticide-free or integrated crop management systems. This will help growers maintain their market share within an increasingly exacting industry.
There may be an economic benefit from the potential to crop an additional flush of mushrooms, though this is not the main potential benefit.
To investigate if portable low pressure steam sterilization reduces pest populations and disease levels on mushroom growing farms without causing undue damage to the tunnel structure or environmental control equipment.
Steam sterilisation report
This is an interim report into the investigation of disinfecting mushroom tunnels by stream sterilisation.
There is a continuing need within the mushroom sector to reduce pest and disease populations. Emptying mushroom tunnels especially after a disease outbreak can be a serious hygiene hazard to the whole farm. When compost bags are emptied either inside or outside the tunnel, spores of mushroom pathogens are released into the air providing a major source of contamination for the rest of the unit.
Steam sterilisation could be an important element in disease control and reduction of chemical use. This is becoming more relevant particularly with demand from consumer groups for lower chemical inputs.
This project was set up to ascertain if steam sterilisation reduces disease levels in mushroom bags and thereby reduce the level of disease contained within the whole unit. A replicated trial was designed to investigate optimum ‘cook out’ temperature and time for disease control under local conditions. This preliminary report outlines progress to date.
The assistance of colleagues in the Department of Agriculture and Rural Development (DARD), growers James and Dermot Tiffney, Portadown and Malachy and Paul Mc Kenna, Benburb and technical input from Kieran Murphy of J.F. Mc Kenna, Armagh, is gratefully acknowledged.
For the purposes of this project it was decided to investigate if steam sterilisation could control the 3 pathogens Cladobotryum, Trichoderma & Verticillium. Compost temperatures of 60oC, 65oC and 68oC at 50mm depth, with three ‘cook out’ times of four, six and eight hour duration were selected. Three temperature probes were placed in each of seven bags chosen at random using a ‘W pattern’. The three temperature probes were inserted in each bag at 50mm, 150mm and 250mm depth. Three of these bags were also seeded with the three pathogens at the three depths, by inserting stainless steel tubes containing inoculated glass vials.
Three bags were sampled before and after each ‘cook out’ by removing a sample of compost from each of the three depths. These samples plus those from the seeded tubes underwent laboratory investigation.
Steam was generated using a HKB Type FR230 boiler producing 400 kgs of steam per hour controlled by a Fancom 765 Computer linked to a laptop computer to record air and compost temperatures at 15 minute intervals.
Findings to date
Air temperature settings
A temperature differential of five degrees was maintained between the required compost temperature at 50mm depth and the set air temperature, e.g. for a bag temperature of 60oC an air temperature of 65oC was required and for a bag temperature of 68oC an air temperature of 73oC was necessary. Figures 1& 2 show air temperatures during two ‘cook outs’. Air temperatures up to 76oC have been reached (after one ‘cook out’ each in three different tunnels) without causing visible damage to the tunnel, the fan housings or lights contained within, although the polythene manufacturers have recommended that a temperature of 75oC should not be exceeded. It is not known at this stage if the overall life span of the house and its fittings will be reduced.
On average the boiler ran for 8 hours before achieving the required compost temperatures. The importance of the ‘activity’ of the compost in achieving high compost temperatures is clearly illustrated below by comparing the length of time required to reach 68oC at 50mm depth in an active compost (Figure 1) with the time required where the compost was considered inactive (Figure 2).
Figure 1 illustrates active compost with the bags reaching 68oC in the top 50mm within 9 hours. Figure 2 shows inactive compost, which required over 16 hours of heating to reach the target temperature of 68oC. Figures 1 & 2 show clearly the temperatures reached in the bags at 150mm and 250mm depth. The 250mm depth is approximately centre of the bag and over 60oC was reached.
Samples of the compost taken before and after each cook out at 50mm, 150mm and 250mm depth underwent investigation for signs of life. The seeded vials containing Cladobotryum, Trichoderma & Verticillium were plated out on selective media.
Initial data suggests that where temperatures between 60oC and 68oC were required in the top 50mm of bags placed on the floor these could be readily achieved whilst temperatures between 58oC and 65oC were obtainable at 150mm depth and between 52oC and 56oC were achieved at 250mm depth. The Fancom 765 computer accurately controlled the ‘cook out’ length to the required settings.
Preliminary results from the compost samples and seeded tubes look very promising. However further ‘cook outs’ are required to complete replicate 2 and 3, before these results can be confirmed.