Cooperative Extension Publications

By I. Kutay Ozturk, Extension Potato Pathologist, University of Maine Cooperative Extension

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Introduction

The information provided below outlines the best practices for cleaning and disinfecting potato handling equipment and storage facilities, an essential part of a complete disease management program for potato production systems.

Potato handling equipment, machinery, and storage facilities regularly encounter various pests, pathogens, and weed seeds. These are contaminating agents and can easily spread between tubers and fields through farm equipment or in storage, leading to issues in subsequent crops unless adequately controlled.

Diseases such as Fusarium dry rot, bacterial soft rot caused by Pectobacterium spp., and late blight can easily spread through seed cutters. Silver scurf pathogen Helminthosporium solani can survive between seasons and bacterial ring rot pathogen Clavibacter michiganensis pv. sepedonicus can survive for three to seven years on equipment and in storage. Considering the potential impact of these diseases, effective sanitization of the equipment and storage facilities is essential.

Cleaning, Washing, and Disinfection

Cleaning and washing the equipment, storage, and surroundings are the essential steps necessary to ensure sanitization of the equipment and facilities. Plant debris, soil, and other materials carried over from the fields prevent the thorough coverage of the surfaces with disinfectants and hinder their efficacy. The first step of sanitization is the physical removal of all visible debris.

Cleaning farm equipment

Cleaning the farm equipment is primarily done by washing with high-pressure hot water and soap or with steaming equipment. Note that both these methods can remove paint from the equipment. The equipment needs to be cleaned at the previous field site or a non-farm site to avoid spreading the contaminated soil to a new field. Cleaning seed cutters are especially important since several important diseases can easily spread during seed cutting. It is highly recommended that the cutting blade be cleaned at least between the seed lots.

Fusarium dry rot, bacterial soft rot (Pectobacterium spp.), and late blight can easily spread by seed cutters. Dickeya spp., Potato Virus Y (PVY) and Potato Leafroll Virus (PLRV) do not typically spread through seed cutters (1, 2, 3).

Cleaning storage facilities

Cleaning the storage facilities starts with the physical removal of plant debris and foreign material. Remove debris such as leftover plant materials, duct tape, wood, metal, and insulation from within the storage area. Clean away the entire storage area by vacuuming, shoveling, and scraping. While still effective in the physical removal of debris and soil, sweeping can also spread pathogens by lifting dust. Clear away any trash or debris that is directly in front of the storage doors. Once all visible debris and foreign matter have been eliminated, sweep the floor over with a magnet to remove all remaining metal pieces on the floor. If the storage facility has a dirt floor, remove the top 1-2 inches of the soil and replace it with soil from a non-potato field.

Once cleaned from the plant debris, soil, and foreign material, wash the entire facility, including walls, bins, floor, and machinery, with hot water and soap or steam, followed by rinsing with water. This helps the removal of dried potato sap or other residues, which can provide shelter for pathogens. Pressure washing on some hard-to-reach areas, such as elevated walls, may not be sufficient, and a ladder might be necessary. Duct pipes should also be thoroughly cleaned to ensure the storage facility is fully cleaned. Steam in itself can be a very efficient disinfectant; however, the elimination of pathogens requires at least five seconds for fresh bacteria and 20 seconds for dried bacteria. Achieving this level of exposure to steam may not be practical for some surfaces, therefore steam application should not be considered as a reliable way of disinfection.

Disinfection of equipment and storage facilities

Complete cleaning and washing of all equipment and storage surfaces before disinfection is essential for complete sanitization. Only after thorough washing and cleaning, i.e., the removal of all soil, plant debris, and foreign material, disinfectants should be applied to achieve sanitization of the surfaces.

Most disinfectants require that treated surfaces remain wet for up to ten minutes to ensure the death of residual bacterial and fungal spores (always check the product label for specifics). The addition of a wetting or foaming agent to the spray solution may aid in keeping surfaces moist for the required period. When disinfecting solutions are used for dipping knives, crates, picking baskets, or foot dip tanks, the solution should be changed frequently to avoid neutralization. There is no one size fits all solution for disinfectant replacement frequency. Regularly inspect the disinfectant solution for signs of contamination, such as visible debris or a change in color or odor. If any of these indicators are present, it’s a good indication that the solution should be replaced. It is very difficult to kill ring rot bacteria in contaminated burlap bags. Preferably, contaminated bags should be burned. Do not reuse contaminated bags for handling seed potatoes.

Potato tubers are in direct contact with the potato storage building surfaces, so the potato storage building surfaces are considered food-contact surfaces. The same is in effect for bin pilers, conveyors, and anything else that handles the crop. Potato storage areas or agricultural commodity storage areas must be on the disinfectant label. Labeling for food processing areas does not apply.

Selecting the Right Disinfectant

It is essential to review the product label carefully before application of any pesticides or disinfectants. Several considerations must be taken into account while selecting and applying disinfectants:

• Is the product currently registered for use by the Maine Board of Pesticides Control?
• What are the safety concerns and personal protective equipment (PPE) requirements?
• Is the product labeled for food contact, potato, or seed potato handling equipment and/or storage facilities?
• Is the product labeled for the right kind of surface (porous vs non-porous)?
• Is a final rinse required?
• What are the environmental hazards, and can the necessary precautions be taken?
• If a specific disease is of particular concern in the equipment or facility, is the disinfectant of choice labeled against it?
• What is the recommended exposure time?

Below are the types of disinfectants that are mainly used in potato equipment and storage sanitization. This list is not exclusive. Additional products may be available and applicable.

Table. Types of disinfectants that can be used for potato equipment and storage sanitization.

Type	Inactivated by organic matter	Surface type	Corrosive to metal?	Safety precautions
Chlorine generating compounds: Significant inhalation risks. Follow safety cautions!
Sodium hypochlorite (Bleach)	Yes	Metal	Yes	Very corrosive. Inexpensive and quick-acting. Rapidly inactivated by soil and organic matter. No residual activity.
Calcium hypochlorite	Yes	Metal	Yes	Very corrosive. Inexpensive and quick-acting. Rapidly inactivated by soil and organic matter. No residual activity.
Chlorine dioxide	No	Metal/wood	No	Less corrosive than bleach. No residual activity.
Non-chlorine generating compounds
Quaternary ammonium	Some	Metal/wood	Slight	Slightly corrosive and safer when diluted. Some residual activity, low level of inactivation by organic matter and soil. Stainless
Peroxyacetic acid/hydrogen peroxide	Yes	Metal/wood	Yes	Low level of corrosiveness. No residual activity.
Phenolic compounds	Some	Metal/wood/ burlap	No	Residual activity. Oral poison.

References

1. Duellman, K. M., Whitworth, J. L., Lent, M. A., Bertram, M. C., & Randall, J. C. (2022). Mechanical transmission of potato virus Y in potato due to seed cutting is not a contributing factor to increased virus in field production. Plant Health Progress, 23, 381-387.
2. Secor, G., Rivera-Varas, V., Johnson, S., Greiner, B., Larson, K., Charkowski, A., & Karim, S. (2021). Potato seed decay and stand loss is not caused by Dickeya spread during cutting and handling of seed potatoes. American Journal of Potato Research, 98, 64-71.
3. Valkonen, J. P. T. (2007). Chapter 28—viruses: economical losses and biotechnological potential In: Potato Biology and Biotechnology (Vreugdenhil D., Bradshaw J., Gebhardt C., Govers F., Mackerron DKL, Taylor MA and Ross HA, eds).

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Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

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