This article appears in the March 2017 issue of Potato Grower.
Chlorpropham (CIPC) is the most commonly used sprout inhibitor for stored potatoes and is associated with most commercial storages. However, seed potato exposure to CIPC can be detrimental to plant emergence and productivity. Contact with CIPC may occur from temporary storage of seed in CIPC-treated facilities.
Seed inadvertently contaminated with CIPC may have delayed emergence, and yield losses can result. CIPC residue on seed as low as 0.6 parts per million can result in more than a 30-day delay in emergence and 36 percent decrease in yield. CIPC label restrictions must be closely followed regarding the cleaning and decontamination procedures necessary for storing seed in a building that has been previously treated with CIPC.
After removal of all potatoes and plant debris, washing and disinfection of storages is recommended. Complete and thorough cleaning of all surfaces (i.e., walls, fans, plenums and ducts) is required for seed to be stored in a treated building. Washing with soap and hot water, pressure washing or steam cleaning followed by a disinfectant spray is the recommended procedure for cleaning potato storages after emptying. In addition, six months must have elapsed since the removal of treated potatoes before storing seed. Removal and replacement of 2 to 5 centimeters of soil from the floor is also recommended. Seed should not be stored in a building that has been treated with CIPC unless label restrictions are closely followed.
Swabbing storage structure surfaces for CIPC residue may indicate the relative contamination level in a building and help ensure the safety of potato seed to be stored there.
A study was undertaken to determine if swabbing walls and other areas in commercial and research storage structures following a systematic method could lead to understanding the level of CIPC residue in the structure and the risk of seed contamination.
In the study, sterile cotton gauze pads were saturated with isopropyl alcohol and used to swab an area (1 foot square) of various materials and locations within commercial and research storage facilities. CIPC residue swabs were collected before and after cleaning and disinfecting research storages. Research bins were pressure washed with hot water and soap, rinsed, and followed with a quaternary ammonium disinfectant application. Commercial storage samples were sampled during the storage season prior to any cleaning. After swabbing, the gauze pads were sealed in plastic bags and immediately shipped to an analytical laboratory for CIPC residue analysis. The residue was reported in parts per million and represents the amount of chemical on the surface of the swabbed area.
Cleaning of storages reduced CIPC residue levels on materials to 0.25 to 22 percent of the levels before cleaning. Residue levels were variable depending on the area and material sampled within the storage facility. Concrete areas in the plenum near the CIPC application port generally showed higher residue than the upper catwalk area. Plastic and concrete may have a higher affinity for CIPC residue retention, and additional care may be needed for cleaning.
Interpreting the results is more problematic than finding them. Based upon these sampling procedures, cleaned and swabbed storages where seed potatoes were stored and subsequently had normal sprout development typically had CIPC residue levels below 20 parts per million. Cleaning and disinfecting storages using the procedures recommended on the label reduced residue on treated storage walls by 80 to 99 percent and resulted in residue levels that reached below 20 parts per million.
This study demonstrated the effectiveness of cleaning in reducing the level of CIPC residues on common materials in storage. This swabbing technique may be used to assess the effectiveness of storage cleaning and airing, and of elapsed time. The technique may also prove useful as a tool for making management decisions on minimizing the potential risk of CIPC exposure with temporary housing of seed.
More in-depth information can be found in the University of Idaho publication “Best Practices for CIPC Residue Sampling of Potatoes and Storage Facilities”.
The authors would like to thank the Idaho Potato Commission and the Northwest Potato Research Consortium for funding this research.