Potato equipment and storages are exposed to a number of pests including fungi, bacteria, insects, nematodes and weed seeds. Many of these pests can be spread from tuber to tuber or field to field on equipment or in storage and cause problems in future crops if not eliminated or at least minimized.
Some disease problems, like bacterial ring rot (caused by Clavibacter michiganese), can be a very serious problem for seed potato producers, even when the disease occurs at very low levels. Nematodes are easily transferred from one field to another in soil adhering to equipment that is not properly cleaned between fields.
One of the best methods to minimize spread or recurrence of a pest is a good sanitation program for equipment and storage facilities. Equipment is often moved from field to field or even shared among growers, a practice that makes cleaning and disinfecting even more critical. This problem is not limited to private farms. The same issues also apply to custom operations and the purchase of used equipment.
It is imperative that all equipment be thoroughly cleaned and sanitized prior to movement into your fields for the first time. If there are known pest concerns in fields within your farming operation, it is advisable to clean equipment prior to and after movement between fields.
Prior to disinfecting equipment or a storage facility, removal of debris and soil is necessary to allow the disinfectant to be effective. This is very important because general disinfectants or biocides are very reactive with organic matter such as soil and debris.
If these contaminants are present in high quantities on the surface you are attempting to disinfect, the disinfectant will not perform well enough. Simply applying a disinfectant without an effective overall cleaning beforehand is not recommended.
Cleaning and disinfecting field and handling equipment
One of the most critical problems associated with contaminated equipment is soil. Most problem pests can be effectively eliminated by removing all soil and debris. Keep in mind that adhering soil is a problem in all field preparation and tillage equipment, and is not just limited to dedicated potato handling equipment. The amount of soil remaining on a piece of equipment varies with the type of equipment. Cultivators generally retain less soil than plows, which, in turn, retain less soil than harvesters.
The No. 1 objective for equipment that is to be cleaned and disinfected is to completely remove all soil. This task can be accomplished with pressurized water or with steam equipment. Clean the equipment at the previous field site or take it to a non-farm site for cleaning so that contaminated soil is not moved to a new field. (Removing contaminated soil at a non-farm site is a very important practice to follow when purchasing, leasing or borrowing used equipment.)
A seed cutter is a common source of contamination for bacterial ring rot, bacterial soft rot, Fusarium dry rot, late blight and, to a lesser extent, mechanically transmitted viruses such as potato virus X (PVX). This occurs because the cutting blades are in use continuously during the cutting process, transmitting sap, debris and the associated pathogens from infected seed tubers to healthy ones.
This highly effective mechanical transmission of seed decay and other pathogens dictates a strong and directed cleaning and disinfection of all cutting blades. At the very least, cleaning and disinfection procedures need to be employed between seed lots.
Cleaning and disinfecting storage facilities
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 “hot spots” where tuber decay had occurred the previous storage season.
Previous research at the University of Idaho showed that silver scurf survived on foam insulation and soil floors for at least nine months and in plywood and sheet metal for three months. Bacterial ring rot can survive on hard surfaces for up to three years and for up to 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:
Before harvest, prepare the storage facility for receiving potatoes by eliminating foreign material. 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.
Remove one to two 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.
Wash the entire facility with soap and hot water or steam; rinse with water afterward. 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 in cleaning equipment because the high temperatures associated with steam make it very effective in dissolving dried materials. For proper disinfection, high surface temperatures must be maintained for several minutes or more.
Be aware of biofilms forming on walls and duct pipes. 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 because the organisms that cause disease in potatoes are capable of surviving on storage surfaces and on equipment under some fairly harsh conditions. Exposure to sunlight is a good final step in the cleaning of equipment or duct pipes, after they have been thoroughly washed and disinfected.
Apply a disinfectant to all surfaces, including 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.
Most important is to keep disinfected surfaces wet with the disinfectant solution for a full 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?
An additional question to ask when selecting a suitable disinfectant is what kind of surface materials are to be disinfected. 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.
Once the surface has been kept wet with disinfectant for 10 to 15 minutes, close the storage for two weeks and open up the doors to air out and dry the storage surfaces. If two weeks is not an option, try to allow enough time for surfaces to dry prior to filling the storage with potatoes.
Professional personnel, such as your storage service provider, can perform all or some of these important steps in preparing for the incoming crop.