The addition of Saltro® fungicide seed treatment to CruiserMaxx® APX seed treatment provided superior yield performance vs similar competitive offerings.
Saltro was particularly valuable in high yielding, early planted fields where seedlings are exposed to greater stress.
High SDS or SCN pressure was not required to realize the value of adding Saltro.
Sudden Death Syndrome Overview
Figure 1. Interveinal chlorosis and necrosis associated with sudden death syndrome. Sudden death syndrome is a primary soybean yield-limiting disease that infects plants early but typically delays symptomology until after flowering. It is caused by a soilborne fungus, Fusarium viguliforme. that overwinters in the soil and can remain viable for several years. Its symptomology is easily recognizable. As toxins produced by the fungus are translocated to the leaves, chlorosis (yellowing) and eventual necrosis (browning and death) of the area between the leaf veins occurs (Figure 1). Plants are often easy to pull out of the ground, as root decay also occurs. A bluish growth at the base of the plant also indicates the fungus is present and active.
There are no in-season management options to SDS once visual symptoms are present because fungal infection occurred when plants were in the seedling stage. The pathogen prefers cool, wet spring soil conditions for infection of soybean roots. Unfortunately, cool soils often coincide with early planting dates utilized to maximize yield by increasing plant nodes and potential pod development.
SDS can also be indirectly managed with improved soybean cyst nematode (SCN) protection. This is because SCN weakens plants and creates entry points on roots for pathogens to enter the plant.1 Most Golden Harvest® varieties utilize the PI 88788 or Peking genes as a source of SCN resistance although either trait can still be potentially overwhelmed in fields with high SCN pressure.2 Adding Saltro to CruiserMaxx APX can provide additional protection against SDS and SCN.
Figure 2. Trial plot treatment setup, 2023.The unpredictability of SDS occurrence and field to field variability of SCN can make it challenging to determine when to invest in additional seed treatments to manage them. Therefore, trials were set up in 2023 to better understand if there is value in utilizing Saltro across all soybean acres, or should it be solely utilized in fields with high SDS and/or SCN risk.
Trial Details
Conducting trials targeted at SCN or soilborne diseases can be very challenging, as SCN populations and disease pressure can spatially differ across short distances creating “hot” spots. To address this, trials were designed in a checkerboard pattern, and treatments were compared to the average of neighboring check plots. In the example shown in Figure 2, a particular treatment, denoted Trt1, was compared to the average of the four check treatments surrounding it (highlighted in red). This method increases the probability that both comparisons are exposed to similar SCN and/or SDS disease pressure.
Table 1. Planting information, SCN populations, and base yield of the CruiserMaxx APX treatment at ten Agronomy In Action sites, 2023. †ND: Not Detectable Ten trials were conducted at eight Agronomy in Action sites to assess the value of adding Saltro to a base seed treatment package of CruiserMaxx APX. Additional competitive seed treatments [Acceleron® + ILEVO® (Metalaxyl, Floxastrobin, Prothioconazole, Imidacloprid + Fluopyram) and LumiGEN® + ILEVO (Oxathiapiprolin, Metalaxyl, Penflufen, Prothioconazole, Cyantranilprole, Imidacloprid, Bacillus amyloiquefaciens strain MBI 600, Bacillus pumilus strain BU F-33 + Fluopyram)] were also compared to CruiserMaxx APX. All seed treatments were applied to the same untreated variety selected for each site to further minimize potential variability (Table 1).
Sites used in the trial represented a wide range of yield environments, planting dates, and SCN pressure (Table 1). All sites except Slater, IA 1, Slater, IA 2, and Waterloo NE exhibited low SCN populations, whereas the three mentioned sites were classified as medium pressure.
Figure 3. Burnt cotyledons caused by a phytotoxic response to ILEVO (Fluopyram) at Clinton, IL, 2023. Soybean Stands
Soybean stands were counted at the V3 growth stage for all sites except Clinton, IL and Janesville, WI. Adding Saltro to CruiserMaxx APX seed treatment did not statistically increase plant stands but did numerical increase them by 1,810 plants (Graph 1). Saltro (Pydiflumetoten) fungicidal activity is primarily focused on fusarium-based diseases which less frequently reduce plant stands, therefore significant stand increases were not expected due to preexisting protection offered by CruiserMaxx APX. However, the Acceleron + ILEVO treatment which utilizes different fungicide and insecticide active ingredients had, on average, 3,388 fewer plants than CruiserMaxx APX (statistically significant at α=0.10). Plant stands of LumiGEN + ILEVO were similar to CruiserMaxx APX (740 less). Differences in final stands could be attributable to the differences in base fungicide activity across the three treatments. It is also possible that any stand reductions with ILEVO treatments may be due to phytotoxic effects on seedlings often observed with its active ingredient (Fluopyram), particularly under cool soil conditions (Figure 3). In comparison, Saltro did not produce any phytotoxic effects on seedlings, as indicated by the positive stand response and visual observations.
Graph 1. Response of plant stands of three seed treatments vs CruiserMaxx APX across seven Agronomy in Action sites, 2023. * indicates a significant response vs CruiserMaxx APX (α=0.10). Field conditions were not very conducive for substantial seedling disease development at most sites. Although several trials were planted into cool soils in mid-April (Clinton, IL, Slater, IA), moisture prior to and after planting was generally well below-average, which likely limited pathogen activity. Despite these unfavorable conditions for seedling diseases, CruiserMaxx APX still demonstrated an advantage to protect plant stands compared to other base seed treatments.
Graph 2. Response of yield of three seed treatments vs CruiserMaxx APX across all Agronomy In Action sites, moderate-yielding sites, and high-yielding sites. * indicates a significant response vs CruiserMaxx APX (α=0.10). Yield Response
Overall, the addition of Saltro increased yield by 1.3 bu/A across all sites when combined with CruiserMaxx APX (Graph 2). In comparison, no significant increases over CruiserMaxx APX were observed with Acceleron + ILEVO or LumiGEN + ILEVO. Segmenting sites into moderate-yielding (55-65 bu/A) and high-yielding (>70 bu/A) categories further showed the value of CruiserMaxx APX and Saltro. At moderate-yielding sites (Blue Earth, MN, Bridgewater, SD, Grundy Center, IA, and Waterloo, NE), Saltro addition did not significantly enhance yield over the CruiserMaxx APX base (Graph 2). In addition to the lower yield potential, these sites were planted in mid- to late-May into warmer soils where SDS pressure was low. Despite this low disease pressure, visual SDS suppression by Saltro was still observed. CruiserMaxx APX did exhibit significant yield advantages of 1.3 and 2.4 bu/A over Acceleron + ILEVO and LumiGEN + ILEVO, respectively. This response demonstrates CruiserMaxx APX is a leading seed treatment option and provides value, even in moderate-yielding environments when disease pressure is low.
The addition of seed treatments with activity against SDS and SCN to CruiserMaxx APX was predominately observed at the high-yielding sites. These sites had earlier planting dates that generally created more stressful early growing conditions (though Clay Center, KS was an outlier). Pairing Saltro with CruiserMaxx APX increased yield by 2.1 bu/A. Overall SDS pressure was still relatively low at these sites, suggesting that Saltro still delivers value in high-yield scenarios, even when SDS or SCN pressure is low.
Summary
A CruiserMaxx APX + Saltro seed treatment offers broad-acre protection against seedling diseases as well as SDS and provides an additional layer of defense against SCN when paired with PI 88788 or Peking genetic seed resistance. This trial also found that adding Saltro can still improve ROI potential, even in environments where SDS and/or SCN pressure is low, especially in intensively managed, early planted fields.
References:
1 Geisler, L.J. and K.C. Broderick. Sudden death syndrome of soybean. 2014. G2243. Univ. of Nebraska-Lincoln Extension.
2 Tylka, G. 2022. High reproduction of SCN populations on PI 88788 resistance is frightening. Integrated Crop Management. Iowa State University. https://crops.extension.iastate.edu/cropnews/2022/10/high-reproduction-scn-populations-pi-88788-resistance-frightening
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