Looking ahead a little, R1 soybeans are not that far away in some of the area. I know that additional inputs on soybean are hard to think about right now, given the already increased cost of herbicide programs for the year. However, the continued wet weather and the cooler temps we are seeing, especially at night, sets us up for a potential disease threat at R1 stage (beginning flowering) soybeans, and that threat is white mold (Sclerotinia).
Key risk factors are fields that are near or at canopy (narrow rows, especially), with high plant populations and higher nitrogen levels. Other heightened risk factors include 1) a history of white mold in the field, 2) soybeans planted on soybean, sunflower or dry bean ground, and 3) reduced or minimum tillage. Tillage reduces white mold by burying the sclerotia and keeping them from “germinating” and producing spores at the soil surface.
As for control, start with cultural methods, like crop rotation, variety selection, wide rows vs narrow rows. Beyond that, here are best management practices for fungicides:
- The timing for soybeans is straight forward- R1 soybeans. White mold infects through the dead flowers on soybean, so infection really is focused to R1 and later.
- Fungicide Products for white mold include: Prothioconazole (Proline) (special 2ee label for SD and ND)- 3 oz at R1, Stratego YLD at labeled rates, and Endura from BASF.
- Domark is labeled for suppression, as are Headline and Priaxor fungicides
- Picoxystrobin (Dupont Aproach fungicide) has been advertised as having activity on white mold. I do not have good local data to support the claim, but the plant health side of any strobilurin is solid, and the pest is labeled on the Aproach label.
- Cobra herbicide has proven itself to provide good suppression of white mold, in addition to weed control.
For another approach on fields with consistent issues, maybe look at Contans. This is a biological control that needs to be applied prior to planting and have tillage to incorporate it. Contans is a parasitic organism that lives on the sclerotia of white mold. It can be effective, is a little difficult to handle and apply.