Management Of Sudden Death Syndrome In Soybeans: K-State Research

 

Sudden Death Syndrome (SDS) is a disease caused by the soilborne fungus Fusarium virguliforme. 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. Losses were unexpectedly low in 2015 considering the generally favorable soybean growing conditions in eastern Kansas.

 

 

Symptoms of SDS are fairly easy to recognize. SDS begins as small, bright, pale green to yellow circular spots on the leaves during late vegetative or early reproductive growth stages. As the disease progresses, the tissue in these spots starts to die and enlarges to form brown streaks between the veins, which remain green. Symptoms are more pronounced on top leaves.

 

 

 

 

 

 

 

 

 

Flowers and pods may abort or not fill. Another key symptom of SDS is substantial amounts of root decay and discoloration of roots and crown. Diseased plants are easily pulled out of the ground because the taproots and lateral rots have deteriorated. Symptoms present on both the leaves and roots are diagnostic for SDS.

 

 

Effective management of SDS requires an integrated approach. Management starts with the planting of SDS resistant varieties. At K-State, we have been evaluating soybean varieties for SDS resistance in our performance test for the past several years. Most varieties are susceptible to some degree, and very few have good resistance. The most susceptible varieties yield 40 to 50 percent less than the resistant varieties at locations where SDS is present and yield levels are in the range of 60+ bushels per acre.

 

 

 

Seed companies also have SDS ratings for most of their varieties, and there is typically a wide variation in ratings. There is little or no correlation between the maturity of a variety and its SDS resistance rating.

 

The presence of SDS is strongly correlated with the presence of SCN. Therefore, where SDS is present, soil samples should be taken to determine the level of SCN present and it will need to be managed along with the SDS. Producers cannot manage SDS simply by selecting varieties that have SCN resistance, however. Some varieties with resistance to SCN are susceptible to SDS. And some varieties that are susceptible to SCN are resistant to SDS. Ideally, producers should select varieties that are resistant to SDS and multiple races of soybean cyst nematode.

 

Cultural management practices that can reduce the risk of SDS infection include delaying planting until soil temperatures are warmer, avoiding planting into overly wet soils, and reducing compaction problems within a field. Producers who have fields with compaction problems should make every effort to correct that problem before planting soybeans next season.

 

Crop rotation also seems to have some positive effect on SDS, but only if the field is not planted to soybeans for four years or more.

 

 

Recent K-State research with seed treatments on soybeans has shown some promising results. A study with a seed treatment applied to irrigated soybean was conducted at the Kansas River Valley Experiment Field in 2015. The seed treatment was applied at the rate of 0.15 mg/seed to five soybean varieties with different levels of tolerance to SDS. The most severely infested plots had about 21% of the leaf area expressing symptoms of SDS by the R6 growth stage. Treatment with the new product ILeVO from Bayer CropScience reduced the amount of SDS and increased yield in the most susceptible varieties, but had no significant effect on already-low disease incidence or yields on the more resistant varieties (Table 1).

 

Table 1. Influence of soybean variety and seed treatment on Sudden Death Syndrome, Kansas River Valley Experiment Field-Rossville, 2015

 

 

In similar research at this Experiment Field in 2013, ILeVO reduced the percent leaf area with SDS at R6 from 18% to 5% on the most resistant variety while yields of that variety were increased from 28.6 to 42.9 bushels per acre. Disease severity was much greater in 2013 than in 2015.

 

In 2014, ILeVO was tested on a highly tolerant variety. SDS severity was very high that year, with about 50% of the leaves showing symptoms in untreated plots. ILeVO decreased to about 15%, and increased yields from 47 to about 58 bushels per acre.