Sudden Death Syndrome (SDS) is a disease that affects soybeans and is caused by the soilborne fungus Fusarium virguliforme (Figure 1). This fungus prefers wet conditions and thus is usually most severe in irrigated fields. SDS tends to be most severe on well-managed soybeans with a high yield potential. It also tends to be more prevalent on fields that are infested with soybean cyst nematode (SCN) or planted early when soils are wet and cool. Historical yield losses from this disease are generally in the range of 1 to 25 percent. While there are differences in susceptibility between varieties, there are no varieties that are completely resistant to SDS. Fortunately for the past several years, ILeVO (Bayer CropScience) seed treatment has shown to be effective at reducing the severity and yield loss to SDS, especially when used in combination with more tolerant varieties. A new seed treatment for SDS, Saltro (Syngenta Crop Protection), will be available to farmers for the first time in 2020.
Figure 1. Soybean foliage with visual symptoms of Sudden Death Syndrome in the study plots located at the Kansas River Valley Experiment Field near Topeka, KS, in 2019. Photo by Eric Adee, K-State Research and Extension.
Testing different seed treatments to control SDS
A research study was started in 2019 to determine the effectiveness of different seed treatments, including Saltro, on SDS in soybeans. Irrigated soybeans were grown at Kansas River Valley Experiment Field near Topeka, KS. The field was Eudora silt loam with pH of 6.4 and organic matter at 1.6%. The previous crop was corn that was vertical-tilled prior to planting. The field had a history of SDS.
Two soybean varieties, NK S39-R9X (four reps) and NK S35-K9X (two reps), were planted at 160,000 seeds/acre on May 16, 2019. Seed in all the treatments had been treated with CruiserMaxx Vibrance seed treatment at 0.0945 mg ai/A. Saltro alone, Saltro with Avicta, Saltro with Clariva, and ILeVO were included in the study.
Soybean cyst nematode (SCN) population at planting was very low (43 eggs/100 cm3 of soil). Rainfall was supplemented with two irrigation events consisting of 0.61 inches each in the last week of July. Plant populations were counted at V1-2 and V2-3, and severity of SDS foliar symptoms were rated every five to six days after onset of symptoms (August 16 through September 3). Disease intensity for the season was calculated using area under disease progress curves (AUDPC) from the four ratings and those values are reported in Table 1. Low AUDPC values indicate better control of SDS. Grain was mechanically harvested to estimate the yield.
Rainfall was above average every month of the growing season, with May (11.28 inches) and August (9.2) precipitation almost three and five times the average, respectively. July (88 oF) was the warmest month, especially during the last half, while August (85oF) was four degrees below average. There were no differences between the soybean varieties for data collected, thus they were combined for analysis.
Summary of results
Foliar symptoms appeared relatively late (August 16) with soybeans at R4 growth stage. The progression of symptoms increased rapidly, however, with individual plots at 40% by August 22. The plant population at V1 to V2 was slightly lower with the ILeVO treatment, but there were no differences in population at V3. Higher yields were closely associated with lower AUDPC values and less severe SDS. Saltro (0.075 mg/A) and ILeVO (0.15 mg/A) seed treatments greatly reduced the severity of SDS and increased soybean yield compared to the control. The addition of the Avicta and Clariva Elite Soybean to Saltro did not alter the performance of Saltro on SDS and soybean yield.
Table 1. Effect of different seed treatments on Sudden Death Syndrome in soybeans from research conducted in 2019 at the Kansas River Valley Experiment Field near Topeka, KS.
|
Treatment |
Plant Population |
Plant Population V3 |
SDS severityy |
AUDPCx |
Yield |
|
|
(plants/acre) |
(plants/acre) |
(%) |
|
(bu/acre) |
|
Control (no seed treatment) |
139,973 aw |
112,966 |
46.2 a |
395 a |
59.5 c |
|
Saltro 0.075 mg /A |
141,167 a |
111,514 |
12.6 b |
66 b |
71.8 ab |
|
Saltro 0.075 mg /A + Avicta 0.242 mg /A |
144,329 a |
113,256 |
5.9 b |
44 b |
70.8 ab |
|
Saltro 0.075 mg /A + Clariva Elite Soybean 0.119 mg /A |
141,425 a |
117,322 |
9.0 b |
48 b |
71.1 ab |
|
ILeVO 0.15 mg /A |
122,259 b |
103,963 |
12.2 b |
70 b |
66.2 b |
|
P-value |
0.039 |
0.30 |
<0.0001 |
<0.0001 |
<0.0001 |
|
CV (%) |
8.8 |
NS |
57 |
77 |
8.2 |
|
y Disease severity estimated September 3 at R6. x Area Under Disease Progress Curve from August 16 – September 3 w Data followed by the same letter or without letters within a column were not significantly different at P< 0.05. |
Take home message
The addition of Saltro as another tool to combat SDS is great news for growers who need to manage SDS on a regular basis. It is not known from this study if Saltro will reduce Soybean Cyst Nematode as successfully as ILeVO has done in previous research. Regardless, this data indicates that both products can significantly reduce the severity of SDS and increase soybean yields. Incorporating either of these two seed treatments, in combination with a partially resistant variety, has the potential to greatly reduce the yield loss due to SDS, and increase the profitability of soybeans production.
Eric Adee, Agronomist-in-Charge, Kansas River Valley Experiment Field
eadee@ksu.edu