- Saltro® fungicide seed treatment has proven to deliver economic returns when sudden death syndrome (SDS) is present and maintain yield potential when SDS is not present.
- Soybeans treated with Saltro outyielded ILEVO® treated soybeans by 1.28 bushels, on average, in 72% of the 141 on-farm trials.
SDS is a widespread soybean disease that can be economically devastating. The pathogen responsible for SDS, Fusarium virguliforme, overwinters in soil and crop residue prior to infecting soybean roots early in the season. Conditions that favor this disease include:
Early planting into cool soil conditions.
- Wet soils that delay emergence.
- Excessive precipitation during the growing season, particularly at flowering.
- Fields with a history of SDS or soybean cyst nematode (SCN).
- Cooler temperatures during flowering and pod fill stages.
Management Options
Although infection occurs very early in the season, foliar symptoms rarely manifest until the late reproductive stages, making in-season foliar applications generally ineffective for SDS management. Delaying planting date for warmer, drier soils can minimize early infection, but this can be challenging depending on the planting capacity of a grower and the number of acres needed to plant. Weather and its influence on favorable planting conditions can also further delay planting dates, resulting in lower yield potential. Selecting varieties with strong SDS tolerance has been the best management strategy until the recent introduction of several seed treatment options. 2 of the most common seed treatments offered are biologicals and succinate dehydrogenase inhibitors (SDHI). The SDHI class of products has proven most effective of the 2 options at managing SDS in previous trials. Less is known about the need to combine variety tolerance and seed treatment management options as compared to using the 2 independently.
SDS Field Trials
A series of replicated small plot and large plot strip trials were established in the 2020 growing season. Replicated small plot trials were conducted at 8 locations by the Golden Harvest® Agronomy in Action research team to evaluate the independent and combined effectiveness of variety tolerance and seed treatments for managing SDS. CruiserMaxx® Vibrance® (CMV) was used as the base fungicide/insecticide seed treatment. Saltro and ILEVO seed treatments were added independently to the CMV treatment base to understand each of their ability to manage SDS and impact on crop safety. A CMV soybean treatment check was also included to understand the value CMV provided for SDS and other diseases and insects. All seed treatments were applied to an SDS susceptible (S) and tolerant (T) variety of similar adapted relative maturity (RM) for each location. Depending on the local RM, either GH2537X (S) and GH2788X (T) or GH3546X (T) and GH3759E3S (S) were planted.
In addition to small plot trials, 142 on-farm strip trials were conducted with local farmers to compare soybean seed treatments across more management practices and a larger geography (Figure 2). Strip trials ranged between 4-54 rows wide and 150–2,000 feet in length. Depending on the location of the strip trials, different combinations of the same 4 seed treatments previously mentioned were used. Typically, only one soybean variety was planted per strip trial location.
Replicated Small Plot Results
Variety differences were present, but the differences were not consistent across trial locations. The susceptible variety often was the highest yielding variety at a location. Yield response from adding specific SDS seed treatments varied across replicated 2020 trials due to different levels of disease pressure. Very few symptoms of SDS were present in untreated plots at any of the small plot locations, indicating that overall, SDS wasn’t a major yield limiting factor in these results. This is also likely why SDS susceptible varieties outperformed tolerant varieties at several sites. When averaged across all 8 locations, neither SDS seed treatment increased yields over the fungicide/insecticide seed treatment check, likely due to the lack of SDS presence (Graph 1). Cedar Rapids, IA, was the only site with statistically significant yield differences. Numerically, Saltro added 1.4 more bushels to CMV and statistically yielded 6 bushels more than the untreated entry at Cedar Rapids (Graph 2). Although no foliar symptoms were observed at Cedar Rapids, there were likely minor SDS root infections or other diseases present that led to yield differences.
Strip Trial Results
SDS presence at strip trial locations was not confirmed, however, it is assumed based upon trial cooperator feedback that SDS foliar symptoms were infrequent at most strip locations. There were several differences between Saltro and ILEVO performance noted in available data. At the 8 locations reporting emergence data, varieties with ILEVO seed treatment had nearly 6,000 fewer plants per acre than CMV, and more than 7,000 fewer plants per acre than CMV with Saltro (Graph 4). Brown necrotic and damaged cotyledons were frequently reported in ILEVO treated plots when compared to other treatments. When averaged across 86 comparisons, adding Saltro to CMV resulted in yield gains slightly less than 1 bushel, although there was a 1.3 bushel advantage over ILEVO treatments (Graph 3). Unfortunately, due to not having a good method to characterize locations for SDS presence, the high number of low disease environments likely masked any observable value when looking across location averages.
The lack of difference between CMV and CMV + Saltro treatments does reconfirm the good crop safety of Saltro. Although final stands were not available at the majority of locations, it can be speculated from locations reporting emergence (Graph 4) that reduced stands from ILEVO were likely part of the reason Saltro treated seed outperformed ILEVO in 72% of the 141 comparisons (Graph 5). If we were able to isolate locations where SDS was high, we would anticipate even greater yield advantages for Saltro. The 2020 strip trial data show a clear performance advantage of Saltro over ILEVO in both emergence and yield.
Summary
Results from these trials show the benefit that seed treatments can provide for managing SDS in soybeans. Due to lack of consistent SDS presence, these trials were unable to determine how the value of an SDS treatment changed when applied to SDS tolerant varieties and susceptible varieties.
When conditions are conducive for SDS development, adding Saltro will help preserve leaf area, maximizing photosynthesis throughout the season and leading to improved yields. In addition to yield, the phytotoxicity symptoms on cotyledons and reduced early vigor observed with ILEVO results in reduced photosynthetic capacity at the critical plant establishment stage (Figure 3). Reduced stands from ILEVO may not always have direct impact on yield. However previous seeding rate trials indicate that once final stands reach less than 100,000 plants per acre, yield loss occurs more frequently. Fields treated with ILEVO should be monitored closely if weather causes inclement soil conditions for emergence. Overall, Saltro appears to provide improved performance over ILEVO in both yield and crop safety.
For more information on Saltro fungicide seed treatment and its protection against SDS, contact your local Golden Harvest Seed Advisor.
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