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36 POTATO GROWER | MARCH 2022 DIGGIN' IN SEED | By Kasia Duellman Using whole or cut seed for managing Fusarium dry rot Big or Small? Over the years, researchers have amassed an abundance of data comparing the pros and cons of whole and cut seed. Recently, my team examined data from 10 consecutive years of field trials comparing the response of cut seed potatoes and small, whole seed potatoes (also known as single-drop seed) to fungicide seed piece treatments that target Fusarium dry rot. Previously published research showed that use of cut seed that was treated with a protectant fungicide seed treatment resulted in less Fusarium dry rot and greater yields (of large tubers and overall yield) compared to single-drop seed that didn't receive the fungicide. However, in this earlier research, no comparisons were made with single-drop seed that was treated with a fungicide. Since then, similar trials at the University of Idaho were designed to include such a treatment, where fungicide was applied to single drop seed. Specifically, we wanted to know if a fungicide seed piece treatment was as effective on whole seed as it is on cut seed in reducing Fusarium dry rot, a disease that can develop during storage, after seed handling and preparation, and after planting. The disease can arise from tuber-borne inoculum or from pathogens that are found in the soil. We also wanted to know if fungicide-protected cut seed would still outperform single-drop seed when it was also protected with a fungicide. What We Did All trials for our 10-year study were conducted at the University of Idaho Aberdeen Research & Extension Center. Russet Burbank seed potatoes from the same certified seed lot were used within each of the 10 years. The six treatments were the same across all the years: 1. Cut seed, not inoculated and not treated with fungicide 2. Single-drop seed, not inoculated and not treated with fungicide 3. Inoculated cut seed, no fungicide 4. Inoculated single-drop seed, no fungicide 5. Inoculated cut seed, treated with fungicide 6. Inoculated single-drop seed, treated with fungicide The fungicide seed treatment we used was a commercially available combination of fludioxonil and mancozeb, and we applied it at the full labeled rate. All inoculated treatments (treatments 3 through 6) were sprayed with a cocktail of spores from laboratory- grown Fusarium dry rot pathogens immediately after cutting and before applying any fungicide seed treatment, to simulate tuber-borne dry rot pathogens. The experiment was established using what is known as a randomized complete block design. This is a standard type of experimental design in agricultural research because it accounts for the natural variation that occurs in a field. Differences in Fusarium seed decay incidence (left) and severity (right) in Russet Burbank (2008-17). Differences in Fusarium seed decay incidence (left) and severity (right) in Russet Burbank (2008-17).