Sclerotina
Symptomes :
Sclerotinia is a brownish rot that can attack plant stems and foliage. Sclerotinia attacks the stems of plants with the symptoms often being the shrinking and collapsing of stems and shoots. It can rapidly kill some plants so act quickly if you have this problem.
Description :
Sclerotinia is a brownish rot that can attack plant stems and foliage.
  Solution :
§ Spraying with a Fungicide § Where practical cut off and destroy infected parts of plants