The recent decision to withdraw the registration of chlorpropham (CIPC) in the European Union (EU) has left a void in available tools for sprout control in storage. The availability of alternative sprout suppression options varies by country within the EU and the UK. Those options currently include caraway oil, DMN (1,4-dimethylnaphthalene), ethylene, maleic hydrazide, mint oil and orange oil. These products are used in combination with cultivar selection and cold temperature storage to minimize sprout development.
The EU sprout control paradigm has shifted, and these options will no longer be alternatives, but will soon become the standard practices. Research is ongoing in the EU and UK to identify novel chemistries and approaches for effective sprout suppression. The global potato industry will benefit from their continued research as they navigate the complexity of developing new sprout control programs.
The fundamental backbone for most sprout control programs in the U.S. includes CIPC. This allows the industry to adequately store and ship quality potatoes year-round to both national and global markets. Additional sprout suppression tools in the U.S. include clove oil, 3-decen-2-one, DMN, diisopropylnaphthalene (DIPN), maleic hydrazide, mint oil and 1-octanol. There is also interest in other essential oils such as oregano oil.
For over 20 years the University of Idah,o in partnership with numerous private and public entities, evaluated alternative products to CIPC and combination programs that include CIPC. Research stretched in multiple directions onto many tangents with the goal to identify products that may suppress sprouting. Many chemistries were tested with varying degrees of effectiveness and success. Some of the chemistries or natural products evaluated included maleic hydrazide, irradiation, biological control agents, 3-decen-2-one, DIPN, hydrogen peroxide, methyl jasmonate, imazamox, imazapyr, pelargonic acid, phosphite, salicylaldehyde, terpene constituents of plant extracts, trans-2-hexen-1-al and numerous essential oils (peppermint, spearmint, muna, clove, rapeseed, artemisia, rosemary, sage, and mixtures of oils). For most of these products, the appropriate thermal application temperature and rate were not known, so applications were made using educated guesses based on the chemical nature and other uses of the product. These educated guesses resulted in some failures (fire, off-gassing, lack of volatility, no impact on sprouting, decay) and some successes (product registrations and uses). In general, if a product showed promise, additional trials were done to address the ideal method, temperature and rate of application, recirculation time, timing of application, and the interaction cultivar and storage temperature had on application methodology.
In addition, studies would look at the impact on processing and fresh quality, wound healing, odor, taste and culinary quality, corrosion potential of storage materials, and disease expression or suppression. Finding, testing, and integrating a new product into the multiple facets of the industry is not an easy task. Continued research is needed in this area to further address solutions for sprout control. This could mean identifying true alternatives to CIPC, as needed in the EU, or recognizing current or novel supplemental products to use in combination or sequence with CIPC for desired sprout control. The latter can be especially significant as the U.S. industry expands the production of new cultivars, with varying degrees of dormancy and sprout behavior, which may demand greater fine-tuning of sprout inhibition.
The application rate of CIPC is determined by storage temperature and the intended length of time in storage. The initial application rate decision is made soon after potatoes are loaded into storage in the fall. But decisions change, such as the need to hold potatoes longer than initially thought, and therefore a second application (re-treatment) of CIPC or a supplementary product may be needed to further control sprouting. Many of the current sprout suppression products available in the U.S. can provide some additional control to extend sprout control in storage, usually via hormonal regulation and/or physically damaging the sprout. This is an area where research in the EU and UK will provide additional solutions for complementary sprout control programs in the U.S.