After an unusually warm start, winter has finally started to feel like…winter. The warm weather that stuck around for so long caused some rapeseed fields to grow a little faster than normal and now we’re seeing some cold injury on rank growth.
The plants will survive this, but cold damaged plant tissue can be a great “breeding ground” for plant diseases like Sclerotinia white mold, so we’ll need to keep an eye on this, especially if it stays wet.
The soil has finally cooled down now as well, meaning root growth has slowed. The purple foliage (below) showing up now is evidence of this.
Purpling is usually caused by phosphorus deficiency in the plant, but before you line up the spreader truck to make an application, remember that the roots must be actively growing in order to take up P. Therefore, when the soil is cool, this symptom commonly shows up even when there is adequate P in the soil. Take a look at the soil temp below.
40 degrees at 4″ is pretty cool and evidently enough to slow root growth. On a bright sunny day, this soil may warm up a few degrees, but probably not much since there is a good bit of crop residue covering the soil in this field. These plants won’t grow much more until the soil warms again in the spring.
Overall, we have a decent looking rapeseed crop so far. Make sure to scout your fields regularly for disease now that many fields have some cold damage present.