Effective farm sanitation strategies.

Effective sanitation strategies for mushroom farms encompass basic growing concepts. Growing strategies include attention to details, anticipation and making a series of compromises. The first two are critical for farm sanitation and hygiene. Attention to details includes farm integrity or maintaining a clean working environment throughout the whole farm.

Another detail is the movement of personnel and equipment around the farm, where "clean" area workers do not go into "dirty" areas and vice versa. Anticipation of the crop environment is important so that appropriate actions can be taken before a disease outbreak or an epidemic occurs.

Educating growers and all personnel about the biology of a disease will help them understand the importance of keeping things clean. Open communications between owners and employees will go a long way in preventing an early infection from becoming a disaster by third break. If your harvesters feel comfortable in pointing out anything suspicious, it may make the difference in catching an early disease outbreak.

FARM SANITATION

A good farm sanitation strategy must begin outside the farm, Figure 1. Having a good drainage system that prevents standing water and keeping weeds, litter, debris, stumps and trash away from the farm will reduce breeding areas and sources of food for many pests and diseases. Immediate removal of spent mushroom compost and mushroom stumps is an important detail, especially in the warmer months with more pest activity.

Inside the farm, a good management strategy starts with identifying dirty and clean activities. Obvious dirty activities include composting, filling, harvesting and emptying. Clean activities would be anytime after Phase II pasteurization and cool down, spawning through casing, including the time up to the first day of harvesting. Another important detail is keeping the doorways, breezeways and rooms dirt free and clear of debris. Keep the areas around the doors clear of clutter and organic matter when workers are not harvesting. Foot baths with disinfectants are only effective when the solution in them is kept at a concentration that is effective. Otherwise, footbaths with a weak solution become a vector of diseases. One suggestion is to keep fresh disinfectant on hand next to the footbath and replenish it every time workers need to clean their shoes, Figure 2.

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Often forgotten in the day-to-day routine is grower movement around a farm. Always start in the clean areas (Phase II, etc.) and move towards the harvesting area, to end up at later breaks. During the first round of checking rooms, look, read temperatures and check moisture and growth; but for other rounds made the same day, look and read temperatures but resist touching the substrate or casing. Check that machinery and equipment are clean during the final inspection each day.

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It's common sense to keep clean area equipment away from dirty area equipment and to clean and disinfect equipment before and after it is used. Before spawning and casing, areas outside the room should be cleaned and disinfected. Another common sense detail is to store spawn and supplement in a clean area and just prior to spawning move the materials outside the room that is to be spawned. Remember to close and seal the doors after spawning.

Casing materials should be stored in clean areas and the area where it is delivered should be sanitary and disinfected. After casing, immediately remove remaining casing mixture from the working area and the growing room.

Harvesters need to be reminded of a few basic rules. They should begin work each day with clean clothes and footwear. Harvesters should always use clean equipment and tools and never carry equipment from older crops or diseased growing rooms to newer breaks. Encourage harvesters to wash their hands and change gloves when moving from one room to another. They should not put their feet on the bed boards and discourage them from putting anything on the bed surface. Communicate to harvesting personnel that they should not touch the diseased mushrooms and molds but should mark the affected areas. After harvesting, equipment, racks and waste bins must be thoroughly cleaned and washed with a good detergent before disinfecting the equipment.

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If disease is present on the farm, all watering and harvesting should be done after a disease crew has inspected the rooms and all diseased mushrooms have been covered. After harvesting, floors should be clean but avoid using high-pressure sprays and brooms; both stir up too much spray and dust. Remove all stumps and dead mushroom tissue from the beds as they are a source of food for Cobweb and Trichoderma. After harvest, floors, walls, shelves, and other equipment/tools must be thoroughly cleaned and treated with disinfectants.

Three Common Diseases--Details for Control

Leonard North and Paul Wuest conducted many experiments that showed that Verticillium Dry Bubble spore to symptom was dependent on spore load and stage of the mushroom's development. Knowing when and what type of symptom first develops is a great detail to help understand when infection took place and the spore load at time of infection. The average symptom development time is about 7-10 days under warm moist conditions, but at temperatures closer to 60[degrees]F it may take as long as 10-14 days. Verticillium spot may develop in less than a day under high spore loads; under low spore loads it may take 2-4 days before the spots develop. When the spore load is high and infection is late in the mushroom's development, split stems will be found. When there is a high spore load and infection takes place early in pin development, the dry bubble symptom is found. With a moderate to heavy spore load and infection occurs later in the mushroom's development, spotting post havest could result.

Cobweb disease control is focused on spore germination and movement. The spores of this pathogen are large and aerodynamic. Although spores are hard to be dislodged by air alone, they are easily discharged into the air by watering or another physical event, such as harvesting or covering with salt. Adie and Grogan in the United Kingdom have done a lot of good research showing that spores discharged by water or salting will travel extensive distances on the bed, Figure 3.

After watering 85 percent of the spores went a distance of 18 inches with the fan off; with the fan on they traveled almost five feet. If possible, turn the fan off when watering or covering disease in a room with Cobweb because it will reduce the distance spores will travel. The important detail when covering a spot of Cobweb is to lay a wet paper towel on top of the infected area and then cover the paper with salt, starting around the edges and working into the center.

Cobweb spores germinate readily in high humidity (100 percent at >97 percent RH) and temperatures of around 70[degrees]F, mycelium grows best at 68[degrees]F. Although growers cannot compromise cropping temperatures, they may consider slightly reducing the relative humidity when Cobweb is present to reduce spore germination. Dead mushroom tissue left on the beds provides not only food for spore germination but moist conditions, even if the room air is dry. Removal of mushroom tissue is a critical component of a strategy to control this disease.

Our lab has recently reported that anaerobic conditions in Phase I and or Phase II predispose compost to infection by Trichoderma Green Mold. The link may be the organic acids produced under anaerobic bacteria have been shown to stimulate the growth of Trichoderma in culture and in compost, with or without spawn, Figure 4.

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We need to understand that these bacteria produce these acids even before growers can see or smell the anaerobic conditions. Therefore, wet dense compost may have low oxygen conditions and not smell anaerobic. Phase II rooms that lack sufficient air/oxygen can also create conditions in some compost that favor these anaerobic bacteria.

Sanitizers & Disinfectants

The Environmental Protection Agency (EPA) distinguishes between a sanitizer and disinfectant by how effective they are and how long they take to work. A disinfectant completely destroys bacteria, viruses and fungi in 10 minutes and may or may not require pre-cleaning. A sanitizer destroys 99.9 percent of the bacteria in 30 seconds, but is effective only on pre-cleaned surfaces. The EPA defines a sterilant as destroying 100 percent of all microbes including thick walled bacterial spores on a pre-cleaned surface.

How effective a sanitizer or disinfectant application is depends on several conditions. The dirt load and surface being disinfected are probably the most important factors around a mushroom farm. The concentration of the chemical used, time it is in contact with a surface, and the temperature at time of application will also determine how effective an application will be.

Components of a good disinfectant include the water quality used, an antimicrobial compound, an oxidant, chelants to tie up available ions like iron or calcium, solvents, and a base or acid component. Probably the most useful component is a surfactant, which has the ability to displace particles and penetrate soil and irregular surfaces. This penetration allows the active killing ingredient to reach the microbes more efficiently, Figure 5.

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