Nathan Kleczewski, Extension Specialist – Plant Pathology; firstname.lastname@example.org; @Delmarplantdoc
Several growers are growing rapeseed this season. A major disease affecting rapeseed is white mold caused by the fungus Sclerotinia. Yes, this is the same white mold that affects our lima beans, snap beans, soybeans, and even sunflowers. The pathogen survives for many years in soils as resistant fungal structures, and when soil is wet and conditions are cool, produce tiny, fleshy “trumpets” that produce infective spores. Spores that land on senescing tissues, especially flower petals, are colonized by the fungus. Once colonized, they can enter the plant, colonize the stem, and choke off water and nutrient movement in the plant. If you planted canola and that field has a history of white mold in other crops, especially if you experienced white mold in this field last season, you may have an elevated level of white mold risk. Other factors that can increase white mold risk include variety (leafier varieties tend to hold more moisture in the canopy), lodging, planting populations (dense plantings favor disease). In my opinion, the dry weather has not been favorable for white mold, but cooler temperatures and potential rains next week may increase the potential for disease development. Fungicides for white mold suppression should be applied when plants are between 20-40% flowering, and there are several options to select from. However, remember to put pen to paper and consider your actual risk level for significant loss relative to commodity price and yield potential.
Below is a risk checklist you can use to determine your potential need for management of white mold in rapeseed: