While sudden death syndrome (SDS) doesn’t appear until early reproductive stages, the fungus infects the plant in early stages. This season is ripe for high infestation as a record-cold April could encourage fungal spores that survive in the soil to germinate.
Researchers first discovered this tricky disease 45 years ago in Arkansas. It claims the No. 2 spot—just behind soybean cyst nematode—for yield loss. While research continues working to contain and control this disease, understand your risk is likely higher this year.
SDS is caused by a strain of Fusarium, which infects the plant very early in its growth—even infecting the seed in some cases. Early planted soybeans are typically at a higher risk since soils are cooler and often wetter. This years prolonged cold could mean everyone needs to watch for the disease if conditions later in the season favor symptomology.
According to Purdue Extension, wet conditions at flowering followed by warm, dry weather encourage symptom expression. If this doesn’t happen the fungus might have little to no effect on your crop. Note, if symptoms do appear (which happens during the R2 stage) there is no rescue treatment.
So how do you defend your crop? It all starts with seed selection, so if you haven’t planted yet keep this in mind. Look for varieties with resistance, consider delaying planting to when conditions don’t favor the disease’s development and look for seed treatments that control Fusarium.
How to Identify SDS in Your Field
Since SDS can mimic other diseases it’s important to learn how to tell it apart. It’s a soilborne pathogen that overwinters in infected residue so pay special attention to fields with a history of the disease. Start scouting in June and keep scouting until mid-August.
Look for these symptoms:
- Yellow, interveinal chlorosis and necrosis after R2
- Leaflets turn brown and drop, leaving bare petioles
- Lower stem cortex will have brown or gray streaks, but a normal pith (not to be confused with brown stem rot)
If SDS appears in fields this year, make note and plan to use seed treatment, resistant varieties or crop rotation to combat the disease.