Storage cleaning and disinfection is important, especially to minimize disease carryover from one season to the next. This is a critical initial step in storage facilities that had tuber breakdown due to rot or “hotspots” where tuber decay had occurred the previous storage season. (read part 1)
Previous research at the University of Idaho showed that:
- Silver scurf (caused by the fungus Helminthosporium solani) survived on foam insulation and soil floors for at least 9 months and in plywood and sheet metal for 3 months.
- Bacterial ring rot can survive on hard surfaces for up to 3 years and for up to 7 seven years on wood surfaces.
The potential for pest carryover from one storage season to the next makes the following cleaning procedures imperative to all farming operations.
Complete storage cleaning and disinfection consists of the following steps
1) Remove plant debris and foreign material. Before harvest, prepare the storage facility for receiving potatoes by eliminating foreign material. Clean up trash such as old tubers, duct tape, wood, metal, and insulation inside the storage. After removing all visible foreign material, pass a magnet over the floor to collect remaining metal contaminants. It is equally important to clean trash and debris that may have accumulated in the area directly in front of the storage doors.
2) Remove 1- to 2-inches of dirt floor and replace with non-potato soil. This step is often difficult to accomplish in a timely manner and one that often can be overlooked. If silver scurf infection is a perennial problem in the storage, or is of great concern, this is an important step to reduce disease spread. Growers who have had bacterial ring rot on their farm should replace the upper layer of soil in their storage facilities as well.
3) Wash the entire facility with soap and hot water or steam, then rinse with water afterwards. Washing is probably best accomplished with a pressure washer using hot water and detergent. Soap-based detergents are often fairly effective disinfectants in their own right, but are particularly effective at dissolving dried potato sap or other residues that might be adhering to floors, walls, or equipment.
- Steam washers can also be extremely effective for equipment cleaning because the high temperatures associated with steam make it very effective in dissolving dried materials. Unfortunately, steam cleaners cannot be relied upon to maintain the extremely high surface temperatures required for thorough disinfection for the length of time needed. For proper disinfection, high surface temperatures must be maintained for several minutes or more.
- Walls/duct pipes; beware of biofilms. Remember also that some pressure washers may lack sufficient pressure to reach elevated areas of interior walls, and a ladder may be necessary. Duct pipes must be thoroughly cleaned as well. Simply setting them outside in the sun will not do an adequate job of cleaning. This is because the organisms that cause disease in potatoes are capable of surviving on storage surfaces and on equipment under some
fairly harsh conditions. They do so in clumps or films of cells surrounded and protected by dried bacterial slime, dried plant sap, or other materials. These structures are referred to as “biofilms.” Biofilms not only allow some bacterial cells to survive, but can also be very difficult to dissolve and remove. - Exposure to sunlight is a good final step in the cleaning of equipment or duct pipes, after they have been thoroughly washed and disinfected.
4) Apply a disinfectant to all surfaces. This section also applies to equipment used in potato production and handling systems. A thorough and complete coverage of all surfaces is needed—including plenum, duct pipes, storage bay, and fan house.
Keep disinfectant wet for 10 minutes. There are a number of approved active ingredients, all of which have similar efficacy provided some simple guidelines are followed. Most important is to keep disinfected surfaces wet with the disinfectant solution for at least 10 minutes. This length of exposure has been shown to effectively kill pathogens likely to be on equipment and in the storage facility. Check the label of the disinfectant to see if rinsing is required. Before using any disinfectant be sure that the product is labeled and registered in the state where you are using it.
Selecting storage disinfectant
The following questions may be helpful in the initial selection of a storage disinfectant. Check the label (and supplemental label) for the following:
- Are there any safety concerns or recommended protective gear (PPE)?
- Is the product labeled for porous surfaces and/or non-porous surfaces?
- Is the product labeled for storage facility and/or potato handling equipment?
- Is a final rinse required?
- Is the product labeled for use only on seed potato facilities and equipment?
Role of surface in choosing a disinfectant. An additional question to ask when selecting a suitable disinfectant is what kind of surface materials are to be disinfected.
Porous versus non-porous. A “porous” surface is any permeable surface such as wood, insulation, or dirt floor. In contrast, “non-porous” surfaces are defined as
being non-permeable, hard and inanimate, like metal,glass, or concrete.
- Calcium and sodium hypochlorites can be corrosive to metal surfaces. In addition, hypochlorites and hydrogen peroxide products are both readily inactivated by organic matter and therefore are not as effective on soil and wood. Soil- and debris-free conditions are vital to obtaining maximum effectiveness with these types of materials.
- If using chlorine-based compounds, buffer the solution to a pH of 6.0 to 7.5 for maximum effectiveness. Avoid mixing chlorine compounds with hot water or with other products unless the practice is specifically allowed on the label.
Disinfect for 10 to 15 minutes; close storage for 2 weeks. One of the most important points to follow is to keep surfaces wet with disinfectant solution for a minimum of 10 to 15 minutes. Once this step is complete, close the storage for 2 weeks and open up the doors to air out and dry the storage surfaces. If 2 weeks
is not an option, try to allow enough time for surfaces to dry prior to filling the storage with potatoes.
Disinfectant chemistries
The following is a list of common disinfectant chemistries available, but additional products may be available and more appropriate to the surface that needs disinfecting:
- Sodium hypochlorite
- Calcium hypochlorite
- Ammonium hypochlorite
- Chlorine dioxide
- Copper quinolinolate
- Quaternary ammonium
- Hydrogen peroxide and/or peroxyacetic acid mixtures.
This range of chemistries is used in different brands produced by different manufacturers, and there are many variables as to percent of active ingredient, allowable application rates, and whether or not the product is labeled for potato storages and handlingequipment. Professional personnel, such as your storageservice provider, can perform all or some of these important steps in preparing for the incoming crop.
Clean storage before storing seed potatoes
Cleaning your storage is also an important step once the crop is removed and prior to storing seed potatoes for cutting and planting. This is especially significant
for commercial growers who had previously applied the sprout inhibitor chlorpropham (CIPC) with the potential of residue remaining in the storage. Mild to severe delays in emergence and growth can occur if seed is exposed to CIPC residues. It is recommended to avoid storing seed in a storage that has been treated with CIPC until one year has lapsed since treatment and the storage structure and ventilation system have been thoroughly cleaned. Always refer to the CIPC product label for specific guidelines and restrictions for subsequent seed storage.
Nora Olsen is a University of Idaho Extension Potato Specialist located at Twin Falls. Phil Nolte is a UI Extension Seed Potato Specialist located at Idaho Falls.
