This is one of the most difficult questions to answer because there are many things to consider. I also don’t want to be outright negative because we do still have options for sclerotinia management in sunflowers. However, management is the operative word.
First of all, sclerotinia head rot infections have an interesting pathway. Spores use dead sunflower florets, plus pollen, as the base to infect a sunflower plant. The spores grow into the receptacle, infecting and decaying the entire head after a period of time. Sclerotinia wilt (basal stalk rot) and mid-stalk rot are also infected by the same sclerotinia species, but it will be via the mycelia that grow from the sclerotia bodies in the soil for basal stalk rot. Mid-stalk rot is also infected by ascospores, but this can be earlier in the season than head rot or at the same time.
So, management of sclerotinia does not start at flowering. Crop rotation is the most obvious management tool that we are familiar with in sunflowers, but it is not reliable. Yes, always put at least three years between sunflower crops and any other oilseed that is a host to sclerotinia, but sclerotia bodies have a long life in the soil and it feels impossible to get rid of them.
Here are some additional management tools that, if layered, will definitely help manage the potential of sclerotinia infections of any kind, in any crop:
Nitrogen – avoid excess nitrogen rates, as this will encourage dense vegetative growth and prime conditions in the lower canopy for sclerotia development.
Weed control – many broadleaf weeds and volunteers can be host to sclerotinia, which can multiply sclerotia in the soil after a season of successful weed infections.
Click here to see more...