A Report on Recent Work on Mushrooms in Belgium 1995-1999

Peter Flegg

(B. Desrumaux, P. Sedeyn, A. Overstijns, H. Desmedt, A. Werbrouk and P. Lannoy, Provinciaal Onderzoek – en Voorlichtingscentrum voor Land-en Tuinbouw, Proefcentrum voor Champignonteelt, Province West Vlaanderen, 336 pages with French and English summaries)

White Button Mushroom

Amounts of water applied from casing to ruffling.
Applying 10, 20, 30 and 40 litres of water per square metre to mushroom beds from casing until the casing layer was ruffled (about 1 week) had no significant effect on crop yields. Measurements of the water content of the compost showed that the upper layer of the compost loses water and the bottom layer becomes wetter. The higher levels of watering hardly affected the water contents of the upper and middle layers of compost but the bottom layer became increasingly wetter with the heavier waterings. It is concluded that much of excess water applied drained through to the bottom layer. Even though the bottom compost layer reached a water content of 80% yields of mushrooms were not affected. Adding a water-absorbent polymer to the upper layer (5 cm) of compost did not affect yield. The water content of the casing layer was hardly affected by the amount of water applied.

Pesticide phytotoxicity
Three pesticides, diflubenzuron, teflubenzuron and a commercial nematode preparation continaing S. feltiae, which are used to control sciarids, were tested for their effects on mushroom cropping. Although the yield of mushrooms following treatment with diflubenzuron was 1.07 kg/m2 lower than from the untreated beds (35.3kg/m2) none of the pesticide treatments significantly reduced yields nor was the average weight per mushroom affected. The conclusion is that all three pesticides can be used watered onto the casing without any adverse effects on cropping.

Cac-ing materials
Over three experiments the use of sterile cac-ing spawn and fully spawn run compost were compared for their effects on the mushroom crop. Neither crop weight nor average mushroom weight were affected by the type of cac-ing material used, but mycelial growth into the casing was slower and less dense when cac-ing spawn was used. As a result, greater care in watering was needed on the beds receiving that treatment. The use of fully spawn run compost resulted in the first and second flushes starting two days earlier than with cac-ing spawn, but the difference had disappeared by the start of the third flush.

Spawn running temperature
Compost from the same source was kept in two separate tunnels during spawn running. One was maintained between 25-27°C and the other between 30-32°C. After spawn run was completed, half of each tunnel was suppplemented with a standard material at 1kg/m2. Yields after three flushes from each of a series of 4 experiments, showed no statistical differences although the ‘high’ temperature spawn run treatement resulted in a crop of 27.74 kg/m2, 5.4% lower thatn from the ‘normal’ spawn run termperature treatment. There was, however, a noticeable crop loss from the high temperature treatment in two of the experiments and in one experiment supplementation increased the crop loss. As a result, it is considered advisable to avoid high temperatures (above 30°C) during spawn run.

Four commercial supplements were compared over a series of 4 experiemtns using the application rate of 1 kg/m2. None of the four supplements Champfood, Champlus-For, Millichamp 3000 and Substradd Forte caused any problems with over-heating and no significant differences between them in resulting crop yields were found. They all yielded between about 4-5 kg/m2 more than the untreated control.

Supplement dose rate
A combination of four rates of filling spawn run compost and three supplement dose rates was used in a series of 5 experiments. The crop yields from filling compost at 85, 90 and 95 kg/m2 were significantly different, a higher fill rate resulted in a better yield. Differences in yield resulting from adding supplement at 1.4 and 1.8 kg/m2 were not statistically significant between each other but both were significantly greater than from the lower supplement dose rate of 1kg/m2. It is pointed out that increasing both the fill rate and the supplement dose rate can have a beneficial effect on crop yields but a supplement dose rate above 1.4 kg/m2 does not increase yield further. A warning of possible crop loss when increasing supplement dose with poor quality compost is given.

Dry bubble resistance to Sporgon
Twenty-four samples of Verticillium fungicola collected by the Belgian Mushroom Research Institute Consultancy Service were tested for resistance to Sporgon. After five replications of the tests it is concluded that a total resistance does not exist, but the sensitivity to Sporgon of the isolates derived from the farm samples varied considerably.

Use of a bacterial formulation against sciarids
A formulation of Bacillus thuringiensis has been tested for its efficacy against sciarids and compared with diflubenzuron. No adverse effects on yields of mushrooms were found and mishapen mushrooms were not a problem. Whereas the B. thuringiensis product reduced artificial infestation by 56% when applied at spawning and 66% when applied at casing, the diflubenzuron product resulted in reductions of 89% and 98% respectively.

Phytotoxicity of Sporgon when used with cac-ing
In crops grown with the use of cac-ing and the ruffling technique, doses of Sporgon at 1, 2, 3 and 4g/m2 reduced the four-flush yield of mushrooms. The crop loss was greater with increasing dose rate and losses were incurred over all four flushes. The main reason for loss of crop is given as the high concentrations of Sporgon in the upper layer of the casing layer. Not even the highest dose rate of Sporgon produced detectable residues in first flush mushrooms.

Variation of mushroom colour with flush number
The effect of flush number on the colour of mushrooms was evaluated over 7 experiments. Only closed mushrooms free from casing material and bacterial blotch were examined. A distinct difference in colour between mushrooms of the first and second flushes and the third and fourth flushes was found. The later flushes had a lower lightness and a higher yellow/blue colour, that is, they were slightly darker. Little difference between the first and second flush could be found.

Effects of calcium chloride solutions used for watering on crop quality
Several series of experients on various factors relating to watering the beds with calcium chloride solutions have been carried out. An early series showed no adverse effects on yield of watering with 0.1, 0.2, 0.3 and 0.4% solutions and no benefits to crop quality either. Whether the hardness or softness of the water affected the outcome was also tested. The degree of hardness of the water had no major effects when no calcium chloride was present, but the use of water of medium hardness resulted in slighter better quality mushrooms (colour) after several days storage than did the use of hard water. This effect, though, was noticeable only in the later flushes. The possibility that degree of water hardness could affect the effect of calcuim chloride was further tested by including soft water (rain water) irrigation in some experiments, but it was concluded that the positive effects on crop quality of irrigation with calcium chloride solutions must be due to other factors than water type. Under Belgian/Dutch conditions the use of calcium chloride seemed to have no value. Following a further lengthy series of tests, it was concluded that the use of calcium chloride could have a positive effect but mainly on mushrooms after a lengthy (6 days) period of storage. Small crop losses and increased dry matter content of the mushrooms were thought to be related to the increase in casing layer salinity caused by using calcium chloride.

Minerals, microelements and supplements
Earlier tests showed that little or no further benefit in yield was gained by increasing the supplement dose rate from 1.4 to 1.8 kg/m2. A series of 5 trials was conducted to find out if adding a mixture of minerals and microelements had any effect. A commercial product, Micromax, was used. Although the addition of both supplements and the mineral mix separately resulted in increased yields, there was no interaction. Adding the mineral/microelement mix at a higher dose rate did not give a further significant increase in yield and the effects on crop yield of the mix are reported to be irregular. Adding the mineral mix did not improve the performance of the higher level (1.8 kg/m2) of supplements. Further trials with Micromax alone confirmed its beneficial effects on yield but the results were irregular. The possibility that this relates to variations in the composition of the poultry manure used to prepare the substrate has yet to be confirmed. Chemical anlayses indicated that it may not always be true to think that poultry manure always contains enough minerals and microelements to guarantee maximum yields.

The Oyster Mushroom

Adding corn steep liquor to the substrate
Adding 0.5% corn steep liquor to the wet substrate confirmed the results of previous tests, giving an increase in yield of 4.85 kg of mushrooms per 100kg of pasteurised substrate. There were no differences between two products, which were tested. The 27% yield increase is described as economically important and consequent increases (1-2°C) in substrate temperature resulting from adding the liquor are regarded as irrelevant. However, a further series of tests comparing corn steep liquor and a dried variant showed that only the dried variant gave a significant yield increase thus contradicting previous results obtained with corn steep liquor. There was also considerable variation in the results, more experiments showing no effects than those which showed benefit. Given this inconsistency in the results the report states that further experiments are needed, but points out that so far no adverse results have been obtained.

Plastic bag perforations
In a series of 4 experiments the effects of the number of holes and area of production surface were examined. In vertical plastic substrate bags, perforations on both sides instead of only on one gave a higher yield per weight of substrate which was statistically significant, but there was no difference between having 168 holes instead of 84. It is concluded that the distribution of holes is more important than their number. Testing the effects of the hole diameter, numbers of holes and the total fruiting surface area showed that yield was improved by increasing hole diameter and by an increase in the number of holes when the fruiting area was kept the same.

First report of a disease
In 1999 the Belgian Mushroom Research Centre observed outbreaks of a disease caused by Stemonitis herbatica. The disease is a myxomycete (a slime mould) and affected substrate and fruit bodies. This is believed to be the first report of such an infection. Spread of the disease in healthy crops is thought improbable.

For copies of the full report or for further information please contact:

Proefcentrum voor Champignonteelt
Iepersweg 87
B8800 Rumbeke,
Phone: 00 32 51 261 430
Fax: 00 32 51 240 020
Email: bernard.desrumaux@west-vlaanderen.be