(also stem break), a harmful disease of flax caused by the imperfect fungus Kabatiella, or Polyspora, lini. Brown spots form on the leaves, stalks, bolls, and seeds. Browning is encountered in many flax-growing regions. Constrictions of destroyed tissue form at the root collars of the shoots, which then fall. The affected stems break easily. The fiber separates poorly from the shive and is low in quality. The seeds become frail, with decreased germinating power. During the vegetative period, the pathogen of browning is spread by conidia, aided by insects, in particular large flax flea beetles (Aphthona Euphorbiae F.). The pathogen survives on seeds and on plant residue in the soil for two or three years.
Control measures include destruction of the beetles, treatment of the seeds with fungicides, and the implementation of other practices that contribute to better growth and development of the flax plants.