Pest populations usually are high in older rooms, and they threaten infestation of younger crops if they are not contained. Since mushrooms are grown inside environmentally controlled rooms, our industry is in a unique position in agriculture, we are able to control pest movement into and out of growing rooms. Once a room is pasteurized successfully, pests will have to enter in order to become a problem. If exclusion were completely successful, there would be no need for any other form of pest control for most diseases. This is especially true in the winter months when pests should be virtually nonexistent. There are several ways to accomplish exclusion:
- the integrity of the building must be maintained
- openings must be secured (doors, fans for boiler or electric rooms, etc.)
- air entering rooms must be filtered
- the movement of people and equipment must be restricted.
Growers doing Phase II filling need to take extra precautions. Since the compost was pasteurized before it is filled into the rooms rather than after fill, the compost is not in the "sealed" environment of the room while it is being filled and, there is not a later pasteurization. Extra care must be taken for sanitation and to ensure the compost is not contaminated during the filling process, since it will not be pasteurized once it is inside the room. For example, conveyors must be kept clean and sanitized, something that is not much of an issue with Phase I material. In addition, the fill crew and all equipment (especially shoes/boots) have to be clean and use proper sanitation procedures.
Construction of new growing rooms must permit easy sealing of the building and provide easy maintenance of that seal. Moldings along rooflines, for example, can hide cracks between the wall and roof. Sometimes air handling transitions or ducts are not installed tight against the ceiling. The space between the duct and ceiling can be so small that it is impossible to seal the area where the wall and ceiling join over the duct. Remember, the extreme environmental conditions produced during a normal mushroom crop, particularly during pasteurization, can be very stressful on a building. Cracks can develop that were not there during inspection prior to cropping. Building materials also are important. Because it is organic and porous, wood can be a good hiding place for pathogenic organisms. Porous cinder blocks and concrete also provide refuges for organisms, particularly in the floor, where it is nearly impossible to develop high temperatures. Consider inorganic, smooth, dense construction materials whenever possible. Plastic and aluminum are good choices, though cost often precludes their use.
Inorganic insulation is a must. Sawdust, for instance, can become a breeding ground for pest organisms. Don't overlook the obvious entry points in any building, such as drain holes (Figure 1) or the webbing in blockwork. Unless the top of the wall is capped, there are thousands of passageways within the wall through which flies can pass. In an existing facility, mortar and caulk are inexpensive alternatives to chemical pesticides or crop loss. When a growing room is empty, inspect for cracks and any other damage that may have occurred during the crop. Buildings expand and contract from the changes in temperature during cropping. High humidity causes wood to swell. Where dissimilar materials come together, such as wooden doorjambs against block walls, the different expansion rates of the materials cause cracks to develop between them. All of these areas must be inspected, and sealed as needed (Figure 2).
Figure 2. Rooms can be sealed with urethane insulation. Photo: PA Mushroom IPM Handbook
Turn off the lights inside the room and look for light penetration from outside. If a growing room has a spring roof, this area must be checked. Ceilings are especially susceptible to damage, particularly if the temperatures during pasteurization are allowed to get too high. High temperatures can damage insulation; sprayed-on polyurethane can buckle and crack. Nailed insulation sheets can buckle, pulling the nail heads through the insulation and leaving access holes through which pests can enter. Pasteurization at the end of a crop is also a good time to check lofts, since steam will escape through openings in the ceiling. Mark these openings and have them repaired.
Limiting and sealing access doorways is of particular importance. Only one or two doors in a plant or any mushroom building should be used as entrances. All other doors should be sealed. Doorways used for entrance and exit must be sealed around the edges, and there should be a threshold at the bottom to seal the door when closed. Seal these doors with weather-stripping or strips of filter material (Figure 3).
Figure 3. Filter material used to seal doors. Photo: PA Mushroom IPM Handbook
Spray the sealed edges with oil or adhesive as an additional barrier against pest entry. A step mat with a sanitizer should be placed at the entrance to sanitize shoes. Clean the mat regularly or it could become a source of infestation. It is better to not have any mat than to use a dirty one. Entrance doors into the growing rooms should be treated the same way as the entrance to the hallway or the plant itself. If there is more than one door into the growing room, one of them can serve as the entrance and the others can be sealed completely. If doors must be kept open for ventilation during Phase II, they should be covered with fly netting or filter material. Filter media must be impervious to fly penetration. What may look impervious to us may not be to a fly. Flies can get through much smaller holes than their body size suggests. Only by testing the filter material or fly netting can a grower be confident flies cannot get through it.
Choosing Filter and Fly Netting
Testing can be accomplished in a variety of ways. First, inspect the material. Holes large enough to permit the passage of flies may be obvious. There are other considerations for choosing filter material instead of netting for a particular application. With netting, excluding flies is enough, but filters are expected to remove spores and dust particles. When deciding which filter to use, you should know what quantity of dust and spores a filter can trap, in addition to knowing that it can exclude flies. Once a suitable material is found and attached to a door, filter frame, or other opening, the edges must be sealed. Flies are tenacious in their attempts to enter a mushroom house. They can smell compost and will mill about the outside until they find a way inside. The simplest method to seal the edges is to fold over the material and staple the edge directly to the doorjamb.
Additionally, an adhesive like Tangle Trap improves the edge seal. Flies snared by the adhesive not only are incapable of crawling under a filter but also are prevented from finding other cracks. Spray adhesive on netting and filter seams, doorframes, fan openings, and filter frames. There are times when an entranceway must be opened for a very good reason early in the crop cycle. Unfortunately, this is the most critical time for fly control in the crop cycle. When performing these tasks, limit the time the door is open and take precautions to prevent infestation or contamination. When employees bring equipment or materials into the growing rooms, they must keep doors closed when not actually entering, or exiting the room. Train them and remind them constantly. Teach your employees the importance of keeping doors closed. Lastly, spray the edges with fly trapping material. Though not as susceptible to disease organisms as cooldown and spawning, the casing operation and casing preparation can have pest problems. Phorid flies are attracted to actively growing mycelia, and Verticillium spores can infest the casing. Take the same precautions during these operations as you use during spawning.
Figure 4. Movement of employees between "clean" and "dirty" areas. Photo: PA Mushroom IPM Handbook
Exclusion also involves controlling the movement of people and equipment. Anyone who has been in older rooms--harvesters, maintenance people, supervisors--must not be allowed to enter new rooms they could infest by bringing in contaminated casing or compost, spores, flies, or mites (Figure 4). Exclusion continues to be important toward the end of the crop. At this stage, instead of trying to keep pests out, they must be kept inside the growing rooms. Exclusion now is more aptly called containment. Flies are actively seeking ways out of the growing rooms, looking for fresh compost or growing mycelium, and are most likely carrying pathogenic organisms. Though not as critical as the employees in the spawning operation, harvesters also must be trained to keep doors closed. Filters must be kept intact.
Most of the content of this article has been extracted from the PA Mushroom Integrated Pest Management HandbookPhillip S. Coles - Pennsylvania State University
Lomax, K. M. 1998. Air filter selection. Mushroom News 46:14-16. Authored by Phil S. Coles, Giorgi Mushrooms