What to Do When Shiitake Mushroom Logs Rot in High Temperatures? A Detailed Guide to Prevention and Treatment
?I. Analysis of the Causes of "Log Rot" in Shiitake Mushroom Substrate Logs
1. The Relationship Between "Log Rot" and Temperature
Shiitake mushroom is a mushroom type that fruits under low and fluctuating temperatures, and temperature is one of the most active and most important factors affecting the growth and development of shiitake mushrooms. Generally speaking, shiitake mycelium grows within a range of 5-32°C, with the optimum temperature being 24-27°C; it grows poorly below 10°C and above 32°C, stops growing at 35°C, and dies above 38°C. Under relatively high temperature conditions, such as in a culture solution at 45°C, the mycelium dies after 40 minutes. "Log rot" of shiitake substrate logs generally begins in late July to August. At this time, the logs are in the transition period from fully colonized mycelium to physiological maturity. The air temperature is often above 35°C, and since the temperature inside the bag is about 3°C higher than the air temperature, the mycelium is very prone to dying or losing vitality, resulting in mycelium burning and log rot, and the logs become susceptible to invasion by contaminating microorganisms, leading to high-temperature disorders.
2. The Relationship Between "Log Rot" and Variety
The high-temperature tolerance of mycelium differs considerably among different shiitake varieties. For example, the 135 series strains belong to the low-temperature type, strains such as 939 (9015) belong to the medium-temperature type, and strains such as Wuxiang No. 1 belong to the high-temperature type. Their tolerance to high temperatures differs greatly. For example, last year our province suffered a rare continuous high-temperature weather event, and mycelium burning and log rot were widespread and prominent, but losses varied from place to place due to differences in cultivated varieties. For instance, Songyang County used the Huagu 939 variety, and the mycelium burning rate was only 10%. Pan'an County used the Huagu 939 variety, and the mycelium burning rate was about 20%. In production areas such as Yunhe and Longquan, however, the Huagu 135 variety was used, and the mycelium burning rate reached as high as over 40%.
3. The Relationship Between "Log Rot" and the Altitude of the Incubation Site for Overwintering Through Summer
When the same shiitake variety is cultivated at different altitudes, its performance during the summer can differ noticeably. This is mainly because air temperature decreases as altitude increases, so mushroom farmers should make rational use of natural resources: farmers in high-altitude mountainous areas can choose low-temperature shiitake varieties for cultivation, while those in plains and low mountainous areas should choose medium-temperature and high-temperature varieties.
4. The Relationship Between "Log Rot" and Cultivation Management
Shiitake mushroom production is related to factors such as moisture, nutrients, temperature, air, light, and pH, and the occurrence of "log rot" is directly related to cultivation management. Although shiitake is a light-requiring fungus, it does not need light at all during the vegetative growth stage of the mycelium. Strong direct sunlight has an inhibitory and lethal effect on shiitake mycelium. Therefore, shade work must be done well during the incubation stage. Shiitake is an aerobic fungus; when oxygen is lacking, the mycelium temporarily sustains life through fermentation, but it consumes a large amount of nutrients, and the mycelium tends to age and dies quickly. Therefore, perforation for oxygen supply should be done in a timely manner. In summer high temperatures, shiitake mycelium will suffer from high-temperature disorders; the choice of incubation site and whether measures are appropriate directly determine the success of cultivation. Where stacks are dispersed promptly and cooling measures are well implemented, the rate of log rot is very low, whereas improper management often leads to a large number of logs rotting.
The meteorological department predicts that this year our province will exit the plum rain season slightly earlier than in previous years and will enter high-temperature weather earlier. Shiitake production areas should attach importance to the problem of safely getting shiitake substrate logs through the summer, and take practical measures to strengthen guidance on summer management of logs during the high-temperature season, so as to reduce possible losses.
????II. Countermeasures to Reduce "Log Rot" of Substrate Logs
1. Complete the dispersal of log stacks and arrangement of the yard as early as possible.
Shiitake mycelium is very sensitive to external temperature, and when the air temperature is above 35°C it may cause the mycelium to die. In principle, before the high-temperature season, logs should be dispersed and moved to sites with good ventilation and heat dissipation, either indoors or outdoors, taking care to handle them gently and avoid vibrating the logs, and this should be arranged during the low-temperature periods of early morning and evening. Indoor dispersed logs should be stacked in a "triangle" or "well" pattern, with a stack height of 3-5 layers and ventilation channels left between stacks. During high temperatures, it is strictly forbidden to turn or move the logs, to prevent the logs from being vibrated and the mycelium respiration from intensifying and raising the temperature; special attention should be paid to the summer management of the low-temperature-type, long-incubation-age "135" variety in low-altitude areas.
2. Advocate outdoor shaded shed incubation.
Because outdoor shaded sheds have good ventilation and rapid cooling, they can effectively reduce the occurrence of mycelium burning, and this is a relatively good way to get through the summer. Outdoor shade sheds should be built on the shady side of a hill, with the top and all sides shaded, covered externally with shade netting or reflective film and other coverings, but the shed roof must not be covered with ordinary plastic film, so as to avoid stuffiness and mycelium burning inside the shed; around the sides, trellises can be set up to grow climbing crops such as pumpkin and loofah to improve the shading effect. The shade shed should be made thicker and taller, and bamboo branches, tree branches, and other materials favorable for ventilation can be used to enclose the sides to improve ventilation. For old mushroom sheds, a comprehensive cleaning and insecticidal sterilization should be carried out before entering the shed.
If continuous high-temperature weather occurs, rotating sprinklers can be installed on the shed roof to spray water for cooling before 10 a.m. and after 4 p.m., and interconnected drainage ditches can be dug around the inside of the shed and along both sides of the walkways inside the shed to introduce "running horse water" for cooling. For those not using ditch irrigation with flowing water for cooling, the logs should be placed on the lower layers of the shelves as much as possible.
3. Strengthen the management of logs kept indoors through the summer.
For those choosing indoor summering, it is advisable to incubate in a ground-floor room with good ventilation and cool summer temperatures. In addition to dispersing the stacking density, attention should also be paid to adding shading facilities around the incubation room, such as building a shade awning and hanging shade netting. Around noon, doors and windows can be closed, and in the evening ventilation should be provided to dissipate heat. On high-temperature days, several basins of water can be placed indoors, and fans used for ventilation and heat dissipation, with the relative air humidity controlled at around 70%. Where conditions permit, water can also be sprayed onto the roof tiles to cool them, avoiding room temperatures above 33°C for extended periods.
4. Stop the practice of perforating logs during high temperatures.
During high temperatures, it is forbidden to carry out measures such as cutting the bags and perforating for aeration on the logs, to prevent air from entering the interior of the logs, enhancing mycelium respiration and raising the stack temperature. Perforation for aeration should be chosen when the weather is cool before high temperatures; the number of perforations can be appropriately increased or decreased according to the dry or wet condition of the substrate, with more perforations for logs with higher moisture content, and it should be done in batches within the same room. After perforation, the temperature rises relatively quickly, and ventilation and heat dissipation should be strengthened for 2-3 days to prevent the mycelium from dying due to high temperature.
5. Properly handle contaminated logs.
For local log rot in the early stage, it can be handled by digging out the rotten mycelium block down to healthy mycelium, then coating with a quicklime solution or a somewhat higher-concentration fungicide, to control further spread and damage by the pathogen. For logs that have already been completely burned, the bags can be broken open early and the substrate dried for reuse; in plain areas, shiitake substrate logs can still be made again before the end of September, but short-incubation-age varieties such as L66 and L33 should be chosen. When using contaminated substrate, quicklime water should be used to adjust the pH value, and the sterilization time should be lengthened; it is best to add new substrate, which is beneficial for mycelium incubation.