Eight preventive measures for bagged shiitake mushrooms to safely overwinter the summer, explained in detail
Based on our investigation and analysis of the summer-survival problems in large-scale bagged shiitake mushroom cultivation in Xixia over more than ten years, we have summarized a set of preventive measures for bagged shiitake mushrooms to safely get through the summer. They are presented below for reference.
1. Prevent contaminated spawn
There are many factors that can cause contamination in spawn, for example: incomplete sterilization of the substrate, lax disinfection during inoculation, introduction of pathogens during inoculation operations, air forced in through the cotton plug, respiration or damage during spawn transport, inoculation with contaminated spawn, and other such reasons. If contaminated spawn is used for production, it can harbor incalculable losses.
1.1 Observation of pathogens latent in shiitake mushroom mycelium. Through long-term spawn production and cultivation management, it has been found that during suitable-temperature culture of shiitake mushroom mycelium, the mycelium can grow through visible pathogens such as long-haired mold, actinomycetes and Aspergillus flavus, while mycelium cultured at below 20°C can grow through common pathogens such as Penicillium and pale green mold and continue growing. Once a pathogen area has been crossed and covered by shiitake mushroom mycelium, it is very difficult to distinguish from pure spawn without careful observation. When the contaminants in this kind of spawn are inoculated into fresh substrate, they will regain activity under conditions above 20°C; if temperatures above 33°C occur and shiitake mushroom mycelium stops growing, they begin to spread rapidly and can destroy shiitake mushroom logs in a short time.
1.2 Select spawn free of contaminants. The spawn cultivation process should have temperature-controlled and constant-temperature conditions. If you do not have the conditions for cultivating spawn, when purchasing spawn from large professional research institutions or spawn production units, choose spawn that has not grown all the way to the bottom, which allows a rough distinction of purity in the later stage of spawn growth. When using bottle or bag spawn, remove the 1-2 cm thick layer of old surface spawn. For spawn cultured at relatively low temperatures, especially spawn inoculated through a hole made in the center, selection should be even more careful.
2. Prevent overly wet mixed substrate
Common shiitake mushroom cultivation technical materials state a substrate-to-water ratio of 1:1.2. If the moisture content of the sun-dried raw material is calculated as 15%, the moisture content of the substrate is (1 - 0.15): (1.2 + 0.15) ≈ 63%. After more than ten years of large-scale effect comparisons, controlling the moisture content at 50%-55% is optimal.
The main reason why spring-planted shiitake mushroom logs have too thick a mycelial skin after summer or have too high a moisture content that affects fruiting is that the moisture content of the mixed substrate is too high. The practical operation to solve this problem is to add water according to the substrate. That is, put the mixed raw material into a new cultivation bag, press lightly with the hand, and gently shake off the raw material. If there is no water mark on the bag film, there is a small amount of raw material, and it shakes off cleanly in one shake, that is the suitable moisture content. Among these, if there is no raw material on the bag film, it is on the dry side; if there is a water mark or substrate sticking to it, it is on the wet side. Cultivation bags mixed as described above show a surface coloration of tea-brown alternating with white spots, and the fruiting effect after summer is relatively stable.
3. Prevent latent pathogens in the logs
If pathogens are latent in the logs, devastating damage will occur during the high-temperature period in summer. The control measures are as follows.
3.1 Mix the substrate one day before bagging. Traditional raw materials, from mixing to firing for sterilization, require "mixing the substrate the same day, bagging the same day, and burning with a fierce fire." In this way, the contaminant spores in the substrate have not germinated and are not easily killed in 100°C steam. For example, the spores of the common Neurospora can withstand 130°C under dry heat conditions, and they need 6 hours at 30°C to germinate into mycelium. In spring cultivation, the temperature is around 15°C or even lower. If the substrate is mixed and bagged on the same day, the contaminant spores are in an ungerminated state and are not easily killed by steam. Long-term practice has proven that mixing the substrate one day in advance allows the sawdust to fully absorb moisture and germinate during heating of the pile, making the sterilization effect thorough and stable.
3.2 Closed cooling after sterilization of bagged substrate. Open the stack 2-4 hours after sterilization of the bagged substrate. While keeping the bagged substrate temperature above 80°C, move it into a fully closed cooling room hung with 8 cm plastic tubing, ignite an aerosol disinfectant, and keep it closed for cooling for 3-4 days. This can effectively prevent pathogens in natural air and contaminants adhering to dust on the bag surface from introducing contaminants before inoculation.
3.3 Aseptic operation during inoculation. Through a 2004 investigation and on-site comparison of shiitake mushroom bagged substrate summer survival in the Kaifeng area since 1999, which easily caused devastating bag failure, it was found that finished bagged substrate inoculated in a large room showed soft rot under a sustained 35°C environment, confirming that open inoculation is the main reason for difficulty in getting through summer. Only by inoculating in a well-sealed inoculation box according to aseptic procedures can a stable spawn success rate be obtained, safe summer survival be achieved, and excellent logs be cultivated.
3.4 Position-limited and temperature-limited hole punching. Hole punching is an important measure to promote mycelial growth. The key points of hole punching are: first, each time the punching position is limited to within 2 cm inside the outer edge of the shiitake mushroom mycelial mass, with a depth of 1 cm, using a fixed-length punching needle, to prevent punching into fresh substrate and infecting it with contaminants. Second, do not punch holes when the air temperature exceeds 28°C, to prevent self-heating of the logs after punching from causing mycelial burning or contamination. Third, do not punch holes on wax-sealed inoculation holes, do not punch holes on nodular growths, and do not punch holes in empty areas of the bag film.
4. Prevent high-temperature mycelial burning
The growth temperature of shiitake mushroom mycelium is 5-32°C, with the optimum at 24-27°C. Growth is poor below 10°C or above 32°C, and stops at 35°C. Experiments show that mycelium in mushroom wood still survives after 20 hours at 40°C, and dies quickly at 45-55°C. When you place logs in sunlight at an air temperature of 35°C, the temperature inside the bag film can be measured at around 55°C. Another example: when the temperature is measured under a shade net at an air temperature of 35°C at a height of 30 cm, it is 10-30°C higher than the natural temperature, so the shade shed should be raised appropriately and water sprayed during the temperature adjustment period to cool it down.
4.1 Tightly shade the mushroom shed. Whether building the shed with branches or black netting, direct light must be completely blocked. Ventilation openings can be made on the back side to maintain all-day ventilation, and let the air in the whole shed circulate in the evening and at night. If the shed is built in a bamboo or wood forest, prevent sunlight from passing through light shafts and sweeping across the mushroom bags, causing mycelial burning.
4.2 Prevent self-heating from burning the mycelium. After hole punching, the internal temperature of the logs rises 1-2°C above the surface temperature. When the air temperature of the mycelium-growing environment is above 26°C, stacked logs should not exceed 4 layers, and ventilation should be maintained every day. After the logs are put into the open air, they should be arranged in a single layer on the fruiting shelves to prevent self-heating from burning the mycelium. For mushroom sheds that need to be closed for mycelium growth, when the daily air temperature exceeds 25°C, temperature should be checked promptly and the shed opened for ventilation.
5. Prevent poor ventilation
Poor ventilation can cause the logs to thicken during color change and to be insufficiently dehydrated. The key points are that the shed site should facilitate air circulation, and a 1 m wide ventilation channel should be kept around the mushroom shed. The top shade net and the shed film should be kept at least 0.5 m apart.
6. Prevent contamination of inoculation holes
The spawn inoculated into spring-planted shiitake mushroom logs, because the mycelium has aged and lost its ability to resist contaminants, is easily infected by pathogens if operations or management are improper.
6.1 Prevent overly soft bagging. Logs that are bagged too softly have loose bag film, and the paraffin-sealed inoculation openings are prone to cracking or falling off and contacting air after inoculation.
6.2 Prevent overly thick wax sealing. When the sealing wax temperature is too low, the wax seal is thick but not tight, and the wax surface easily cracks during bag handling or draws air in through the holes. The wax melting temperature should be adjusted promptly to keep the wax seal on the spawn hole surface thin and tight. Among these, if the sealing wax foams when applied to the spawn, the temperature is too high and easily burns the spawn to death; if the surface after application is not smooth, the temperature is too low.
6.3 Prevent puncturing the inoculation holes. During operations such as punching holes to increase oxygen and putting logs into the open air to remove moisture, avoid puncturing the inoculation holes, and it is even more unsuitable to punch holes on the inoculation holes, to prevent air intake or contact with rainwater.
6.4 Prevent rainwater from entering the inoculation holes. During the summer period when logs are on the fruiting shelves, there should be a shed film above the shed to block rain. For logs without shed film, the inoculated hole surface should preferably face upward or be placed on the side.
7. Prevent cold waves from stimulating fruiting
Spring-planted bagged shiitake mushroom varieties that fruit in autumn and winter are mainly medium- and low-temperature types. If inoculated in February-March, they have already entered the color-change stage around the beginning of summer. Stimulation by a cold wave of around 15°C during the spring-summer transition may cause the logs to fruit.
The control measures are: first, close the mushroom shed before and after the cold wave arrives to buffer the temperature difference stimulus, and avoid disturbing the logs during the cold wave. Second, if there are fruiting logs, manage and harvest them according to the normal method of cutting the film to cultivate primordia, to prevent the primordia from suffocating inside the bag film and causing contamination.
8. Prevent poor dehydration of the logs
A relatively high moisture content in logs after summer (dehydration rate below 10%) is a common phenomenon causing difficulty in fruiting. Comparisons of multiple samples of the same variety confirmed that the reasons affecting poor dehydration include: uneven substrate mixing, too much water added to the substrate, logs filled too tightly with substrate, fewer than 40 holes total for hole punching and opening to the air on the logs, poor ventilation around the mushroom shed, and long periods of continuous rain in summer and autumn. Operating and managing according to the above technical requirements reduces the weight of the logs after summer by 20%-40% compared with the time of cultivation. According to different moisture contents, adopt measures to promote fruiting respectively: tapping the logs, water injection, and timed soaking. For logs that have particular difficulty fruiting, you can try closing the mushroom shed and burning an appropriate amount of diesel (kerosene) inside the shed to consume oxygen and promote fruiting.