Yellow Witches' Broom

Order: Uredinales

Family: Lymantriidae

Latin Name: Melampsorella caryophyllacearum Schrter

Common Names: Yellow Witches' Broom


This rust fungus causes abnormal shoot growth on balsam fir. Usually not severe, but can be a serious problem in Christmas tree plantations especially when balsam fir is grown on heavy agricultural soils where chickweed is common.

Life History

This rust fungus infects fir buds in the spring and invades the young shoots. The perennial brooms grow slowly the first year and cause only slight, elongated swellings that are very difficult to detect on infected shoots. The following spring, buds on the infected twigs produce upright shoots that are thicker and shorter than normal. Needles of the new shoots are stunted, thickened, pale green and arranged in a spiral curve. During the summer, the needles become yellow; in autumn they die and drop off, leaving the broom empty of foliage during the winter. The broom produces a new crop of pale green needles in spring which release spores to infect its alternate host, chickweed. When the rust matures on the chickweed, it releases spores to infect the trees.

Damage Symptoms

Trees with visible brooms. Needles that are stunted, turn from green to pale green to yellow, then die and drop off. Branches affected by the brooms are deformed by galls and cankers.

Control Options

Large scale control programs in forest plantations are not practical. Christmas tree lot control would be two-pronged:

  1. Remove the brooms while they are still small. In the case of large brooms, the whole tree should be removed and destroyed. Also, search for mature balsam fir around the plantation and remove the brooms.
  2. Remove the alternate host (chickweed) by means of a herbicide.


CAUTION: Read and follow the instructions on the label when using any control agent. Proper application and use of recommended personal protective equipment are essential for the safe use and effectiveness of any pesticide.

DISCLAIMER: Control options are suggestions only. Actions taken for pest control are the sole responsibility of the applicator in full compliance with any Federal, Provincial or Municipal Acts, Regulations or Bylaws.