Seed potatoes in the Pacific Northwest are routinely cut into 1.5- to 3-ounce pieces before planting, and the cut surfaces provide the perfect entry point for pathogens. Although implementing optimal cultural practices such as allowing seed pieces to heal after cutting under certain circumstances and targeting favorable planting conditions can sometimes effectively protect cut seed from disease, using a fungicide seed piece treatment offers another level of insurance to help protect the seed against seed-borne diseases such as Fusarium seed piece decay, Rhizoctonia stem canker, silver scurf and late blight.
Fungicide seed piece treatments—applied either as a dust, slurry or liquid mist—can protect cut seed pieces and either prevent or suppress development of specified diseases.
Whole vs. Cut Seed
Previous research from the University of Idaho has demonstrated that cut seed, when treated with a protectant fungicide seed piece treatment, can perform as well as or better than single-drop whole seed that has not been treated. More recently, we found that a seed piece treatment (in this case, MaximMz, a combination of fludioxonil and mancozeb) consistently and significantly reduces the incidence and severity of Fusarium seed piece decay, compared to the non-treated control, regardless of whether the treatment is applied to whole seed tubers or cut seed.
In the same study, we also commonly saw yield bumps when a fungicide seed piece treatment is used. The yield bumps were statistically significantly higher for treated seed in three of 10 years. Interestingly, in eight out of the 10 years this study was conducted, single-drop whole seed that received a seed piece treatment of MaximMZ showed numerically better yields than cut seed pieces receiving the same treatment. However, this difference was statistically significant in only one of the eight years. Overall, we have found that fungicide seed piece treatments can have value whether seed is cut or used whole.
Liquid vs. Dust Formulations
How well a seed piece treatment performs depends on several factors, such as how seed pieces are handled before and after treatment, soil temperature and moisture at planting time, disease pressure, and coverage of the product on the seed pieces. Good coverage is key. To this end, liquid fungicides may actually have one up on the dusts. Liquids can lend themselves to more uniform and precise application, they can potentially provide better coverage on whole seed tubers, they can be easier to apply, and they offer the added benefit of improved worker safety. Some liquid formulations are designed to not need a follow-up treatment with a bark or other carrier dust.
The downside of liquids is that they do require more attention to calibration to avoid applying too much or not enough product. Additionally, if treated seed is not handled properly post-cutting, risk of bacterial seed piece decay may increase. In some cases, growers opt to apply a bark product after applying a liquid mist treatment to help dry the cut surfaces. This may be advisable particularly for formulations that require extra liquid to facilitate movement in an application system, such as some of the available mancozeb-based slurries. In our plot trials, we have not found a bark dust to be necessary with liquid products such as CruiserMaxx Vibrance Potato and Emesto Silver when working with small numbers of potatoes and allowing cut seed pieces to dry before planting. What works best for your operation may depend on your comfort level, handling practices post-cutting, and soil temperature and moisture at planting.
Available Treatments
Some of the available seed piece treatments labeled for use in Idaho are listed in the table below. This table only includes examples of those registered as direct seed treatments pre-plant; it does not include others that are registered for in-furrow application (which tend to offer better management of soil-borne pathogens) but not direct application to whole or cut seed.
Before using any product, verify that it is labeled for your state and purpose, and be sure to read, understand and follow the labeled instructions to minimize the risk of injury to the plant, the environment and the handler.
Regardless of what approach you use for protecting seed pieces, even the best fungicide seed piece treatment can be overwhelmed by poor handling practices, improper storage conditions, high disease pressure, or Mother Nature’s stubborn refusal to cooperate. As always, strive to implement a well-rounded, integrated disease management program that includes more than one strategy to reduce the risk of potato diseases.