BADGER BEAT

Seed Potato Treatment Options Studied

Researchers study the effects of early season handling and disease control treatments on potato

By Dr. Amanda Gevens, chair, professor and integrated extension specialist, University of Wisconsin (UW)-Madison Department of Plant Pathology; Shane Hansen, doctoral candidate, UW-Madison Plant Pathology; and Stephen Jordan, outreach specialist, UW-Madison Plant Pathology

Healthy, certified seed and a maximum potato stand provide the best start for a profitable crop. Optimal conditions for planting are sometimes provided by Mother Nature, but growers also prepare for less-than-optimum conditions when orchestrating seed handling and early season disease management in potatoes.

This article addresses some of our recent research as we develop and enhance best management practices to positively influence stand and crop health.

Dr. Amanda Gevens and her team at the University of Wisconsin-Madison Department of Plant Pathology are studying seed potato handling and treatment with the goal of offering an improved understanding of seed and early planting parameters to aid in growers’ decision-making. Outcomes of

Seed cutting and suberization. In these early decisions foundationally drive potato crop yield and quality. Above, cut North America, most growers cut seed potatoes are loaded into a planter seed tubers to create seed pieces. at Mortenson Bros. Farms, Inc. Aside from the treatment of seed, cut and single drop seed statuses have unique benefits. Single drop/whole seed generally provides high vigor, increased stem counts, and increased tuber set, while tuber size tends to be uniform due to heavier set and less disease when compared to cut seed. Spray Foam Insulation & Roofing Comparative advantages of cut seed include reduced cost by extending Specializing in potato & vegetable stock to meet acreage demands, storage facilities for over 45 years. smaller, more uniform seed pieces, 715-424-4200 • 4111 8th Street South • Wisconsin Rapids, WI 54494 and fewer stem counts with smaller www.fencilurethane.com set and larger tubers.

Cutting seed potatoes creates an open wound that can become easily infected by pathogens including Fusarium dry rot and bacterial soft rot.

LIMITING PATHOGENS

Wound healing or suberization at 5055 degrees Fahrenheit with adequate airflow and high relative humidity has long been recognized as an approach to help limit these pathogens from infecting seed. Suberization and liquid seed-applied fungicides. In our University of Wisconsin (UW) Hancock Agricultural Research Station field trials, 20192021, suberization positively influenced potato emergence and yield when coupled with liquid seed treatment of fludioxonil. At 40 days post-planting, emergence of non-fungicide-treated cut seed did not significantly differ between suberization status (suberized versus non-suberized) for Dark Red Norland or Russet Burbank potatoes. When we investigated the use of the liquid seed-applied fungicide fludioxonil in addition to suberized and non-suberized seed potato treatments, we found that emergence was reduced in the non-suberized comparisons. The use of the drying agent Nubark (one example of Douglas fir bark powder—other commercial formulations are available) helped to recover emergence rate and

Figure 1: Shown is dark Red Norland potato plant emergence (%) resulting from UW-Figure 1. Shown is dark Red Norland potato plant emergence (%) resulting from UW-Hancock Agricultural Research Figure 1. Shown is dark Red Norland potato plant emergence (%) resulting from UW-Hancock Agricultural Research Hancock Agricultural Research Station field studies of cut and whole seed potato subjected Station field studies of cut and whole seed potato subjected to suberization/no suberization, and seedStation field studies of cut and whole seed potato subjected to suberization/no suberization, and seed-applied -applied to suberization/no suberization, and seed-applied fungicide/no fungicide/fungicide plus fungicide/no fungicide/fungicide plus Nubark/Nubark alone.fungicide/no fungicide/fungicide plus Nubark/Nubark alone.

Nubark/Nubark alone. Figure 2: Illustrated is Dark Red Norland potato total yield resulting from UW-Hancock Agricultural Research Station field studies of cut and whole seed potato subjected to suberization/no suberization, and seed-applied fungicide/no fungicide/fungicide plus Nubark/Nubark alone.

Figure 2. Figure 2. Illustrated is Dark Red Norland pIllustrated is Dark Red Norland potato otato total yield resulting from total yield resulting from UW-Hancock Agricultural Research Station UW-Hancock Agricultural Research Station studies of cut studies of cut and whole seed potato subjected to suber and whole seed potato subjected to suberization/no suberization, and seedization/no suberization, and seed-applied fungicide-applied fungicide/no /no fungicide/fungicide plus Nubark/Nubark alone fungicide/fungicide plus Nubark/Nubark alone. .

yield when fludioxonil was applied, especially in Dark Red Norland potatoes. The emergence and resulting yield

Relative seed age. WeatherRelative seed age. Weather-related planting delays are common in Wisconsin and other northern production regions. At -related planting delays are common in Wisconsin and other northern production regions. At of whole or single drop seed was not times, seed potatoes are warmed up and in queue for the field when weather delays occur. times, seed potatoes are warmed up and in queue for the field when weather delays occur. impacted by the fludioxonil and/or Nubark treatments. We explored the impact of relative seed age during the warm-up time (55 degrees) and liquid seed-applied fungicide on emergence in an environmentally controlled growth facility at the UW-Madison Department of Plant Pathology. We explored the impact of relative seed age during the warm-up time (55 degrees) and liquid seed-applied fungicide on emergence in an environmentally controlled growth facility at the UW-Madison Department of Plant Pathology. continued on pg. 32

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Figure 3. Shown is Dark Red Norland potato plant emergence resulting from UW-Madison Russell Laboratories growth chamber studies of cut seed potato subjected to differential aging or warm-up time prior to planting. Seed was cut, treated with fludioxonil, and planted after 0-8 weeks of aging. Emergence ratings were collected on a weekly basis for six weeks.

Soil and seed temperature. Seed potatoes planted into soil of temperatures different from that of the seed potentially risk the development of condensation at the interface of seed and soil.

Moisture and seed potatoes are a risky combination with respect to disease management and seed health.

continued from pg. 31

IMPACT OF FLUDIOXONIL

Only cut and non-suberized seed were significantly (negatively) impacted by fludioxonil treatment with a 15 percent reduction in final stand count and a 50 cwt. (hundredweight)/acre reduction in yield (Figures 1 and 2). This 15 percent reduction in the stand was cut by about half (from 15 to 7 percent) when the planting date was two weeks earlier (April 15) rather than later (May 1). For Dark Red Norland, cut, nonsuberized, fludioxonil-treated seed, planted both early and late, resulted in reductions in stand and total yield. As for Russet Burbank, impacts were less, with roughly 5 percent stand reduction in the early planting and no stand reduction (just delayed emergence) in the late planting.

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Neither planting resulted in a total yield reduction. It’s interesting to note, but not statistically significant, that for the purpose of equal comparison in our study, we placed our whole, single-drop seed under the same suberization conditions that we subjected our cut seed. Those conditions included 98 percent

Above, Figure 3: Shown is Dark Red Norland potato plant emergence resulting from UW-Madison Russell Laboratories growth chamber studies of cut seed potato subjected to differential aging or warm-up time prior to planting. Seed was cut, treated with fludioxonil, and planted after 0-8 weeks of aging. Emergence ratings were collected on a weekly basis for six weeks.

relative humidity, high airflow, and a temperature of 55 degrees. We saw numerical increases in yield for the suberized compared to non-suberized whole seed, but there were no differences in emergence. To summarize, best management practices include: 1) Use whole seed when possible; 2) When using liquid seed-applied fungicides on cut seed, always suberize the seed; and 3) When using liquid seed-applied fungicides on cut seed, add a drying agent like Nubark. Relative seed age. Weather-related planting delays are common in Wisconsin and other northern production regions. At times, seed potatoes are warmed up and in queue for the field when weather delays occur. We explored the impact of relative seed age during the warm-up time (55 degrees) and liquid seedapplied fungicide on emergence in an environmentally controlled growth facility at the UW-Madison Department of Plant Pathology.

Dark Red Norland seed started to sprout at two weeks under warm-up conditions, with substantial growth in sprouts at weeks 4, 6, and 8. Seed from each of these time points was then cut, treated with fludioxonil, and planted. Emergence was recorded each week until week 6. Aside from the 14-day emergence rating, emergence did not differ between non-fungicide treated and fludioxonil-treated seed for the five emergence ratings. Non-treated seed consistently demonstrated greater emergence than the fludioxonil-treated seed regardless of age and days postplanting. Notably, at four weeks of age, the seed substantially dropped in emergence by half. This trend continued through six and eight weeks of age (Figure 3).

Fungicide treatment on this 4–8-week-old seed reduced emergence by roughly 10-30 percent compared to the non-treated seed. We will repeat this work, but preliminary outcomes suggest that, once warmed up, seed should be planted within two weeks.

Longer wait times may substantially reduce emergence, especially if seed-applied liquid fungicides are intended.

Soil and seed temperature. Seed potatoes planted into soil of temperatures different from that of the seed potentially risk the development of condensation at the interface of seed and soil.

Moisture and seed potatoes are a risky combination with respect to disease management and seed health.

We evaluated the outcomes of seed potatoes cut and maintained at 55 degrees planted into soils of the following temperatures, 45, 55, and 65 degrees.

Soil moisture and temperature were recorded at the seed-soil interface as well as in the bulk soil surrounding the planted seed piece.

The temperature differential did result in increased soil moisture at the contact site with the seed piece.

More moisture was present in the scenario of 55-degree seed planted

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into 45-degree soil than in the 55-degree seed planted into the 65-degree soil. The differences were most pronounced within the first 24 hours of planting and plateaued between 48 and 72 hours after planting.

SEED & SOIL TEMPERATURES

We will be repeating this work with additional sensors to better understand the relationship between seed and soil temperatures, and moisture, on seed health and emergence.

Outcomes of these early decisions foundationally drive potato crop yield and quality.

Our work has, initially, not included inoculation with target pathogens, however, we have not been excluding pathogens as we utilized commercial seed and have been working in soils of fields with potato-growing history. The results of our work represent outcomes that might be expected in commercial standard operations. Seed or field locations with a heightened risk of diseases managed by seed-applied fungicides may experience different outcomes. We are also cognizant of the different results that come of seedapplied fungicides depending on the applicator tool and volume of fungicide and carrier liquid. These are additional factors that we are considering in our continued work. We appreciate our grower and industry partnerships as we continue our studies in this area of seed handling and treatment. Our goal is to offer an improved understanding of seed and early planting parameters to aid in growers’ decision-making in the early season.

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