Upon checking my records, the area of the field that produces flat stems
was tested several years ago and found to be boron deficient. Pelleted
boron was spread in this area and that may be the problem. If added to a
farm field, it would be mixed with the soil but in a black raspberry patch,
it is top-dressed and, probably, a boron pellet didn't land near plants that
produces flat stems. Does that make sense?