Order:    Uredinales

Latin Name:    Melampsorella caryophyllacearum Schröter

Common Name:    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.

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.

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.

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.