Earlier this week, I looked at some rapeseed with fellow Extension Agent Trish DeHond. This field is showing some light damage from the recent cold. The plants are still in the rosette stage, which is very resiliant to cold injury, so this light damage isn’t very concerning.
The photo below shows a leaf with classic symptoms of cold injury. The white colored tissue has been damaged (burned) by the cold had windy conditions that we saw about two weeks ago. New growth will be fine.
The photo below shows some nutrient stress. Purple coloration is usually a sign of phosphorus deficiency. This is most likely showing up not because we are lacking phosphorus in the soil, but because the soil is too cool for the roots to grow and adequately take it up. Phosphorus up-take will improve as the soil warms back up.
We also found some signs of white mold in the field. This form of white mold is Sclerotinia sclerotiorum and is a totally different species than the white mold that commonly attacks peanuts (Sclerotium rolfsii). This fungi reproduces by forming very dense structures called sclerotia that can survive in the soil for several years. Crop rotation is the best way to prevent white mold from getting started in a field. Prolonged damp conditions are making it easier for this disease to develop right now.
White mold has caused the stem of this plant to rot right at the surface of the soil. The white fuzz we see in this picture and the one above is the mycelium of the fungus. Currently only a very small amount of the field is affected.
Here is what Sclerotinia looks like later in the season on a mature plant. The black masses on the stem are the sclerotia that will fall off the plant and remain in the soil.