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Ask the experts: This strange growth can’t be a broom, but what is it?

Editor’s note: This article is excerpted from a Central Region newsletter and recounts a discussion at the National Meeting in Ohio in 2016. 

Question: This growth is on a fir growing on my daughter’s property near Eau Claire, Wisconsin. It looks like a broom, but not quite. What the heck is it? —Jerry Belanger

Answer (Chris Daeger):  Well, it certainly appears to be a broom. A typical witch’s broom is normally congested and has a much slower growth rate: That is why I question it; as it appears to already have an intermediate’s growth rate or something faster than what the spring’s growth shows on the rest of the fir.

It could be an extremely rare example of a broom exhibiting “giant” tendencies. Yes, we could surmise it being a reversion of sorts since those do have a higher growth rate than the original plant.

If it is just a seedling grown straight species Abies, the growth as it appears now (single attachment question really needs to be determined) then it is plausible that this weird growth was caused by a viral organism. It still can be genetic in nature (a good thing) that caused the original bud to mutate, as a reversion can be as well. Only time will tell and giving some future grafts 10 years to grow and evaluate will prove that it is healthy and reasonably safe to pass it on. If this weird growth is coming from multiple points along that branch, then I’d bet that something disease-related caused all that growth, much like a canker disease.

Additional photos and information were provided: the tree is a straight species Abies.

Well, it certainly appears to be a witch’s broom of some sort since it originates at a single point. Now, what caused it remains a mystery, being either viral or a disease-influenced or a genetic reason. The latter is what one hopes for — those tend to be “graft-able” or maybe “root-able”.

I’d like to gather these shots and present them as a Conifer Sketch at the national meeting. Some additional theories and opinions might help us.

After the meeting:  It’s all bad news. It is caused by fir broom rust (Melampsorella caryophyllacearum) and its alternate host plant is chickweed. It’s not a good mutation for anything and should be removed and maybe even burned. I’d get rid of the branch it’s growing on. You can look up other particulars online if you care to.

After presenting the pics at the meeting I asked the audience if they had any thoughts. Western Regional President and ConiferBase Editor, David Olszyk, recognized it right off; it stumped almost all of the rest of us at the meeting, including me. Definitely a turnaround from the stump the experts session earlier in the morning which went really well!

From USDA Forest Service leaflet 87 July 1964:  “Fir broom rust on true firs (Abies species) is caused by the fungus Melampsorella caryophyllacearum Schroet. The disease is native in almost the entire range of firs in Eurasia and North America. The rust fungus occurs on alternate hosts (chickweeds) beyond this range to 70°N and 50°S latitude. The disease is seldom more than a curiosity in the Eastern States, where few epidemics have been reported since it was first recorded in 1856. But in the Rocky Mountains and Great Basin, many stands are heavily disfigured because a few to dozens of yellow witches’-brooms (sic) occur on almost every fir.

The most conspicuous and easily identified symptoms of fir broom rust are the bushy, upright branch proliferations or witch’s brooms, which bear annual, yellow needles. There are other brooms on fir, caused by mistletoes in the Pacific coast states and the Southwest or by another rust (Milesia pycnograndis) in the northeast, and occasional brooms of unknown origin, but only Melampsorella causes marked loss of chlorophyll and annual casting of all broom needles.”

Additional information: Cornell University reports that, “over the past few years fir broom rust has become a problem for some Christmas tree growers in upstate New York. As the acreages of Fraser and other firs increase we are likely to see more of this disease. In the worst cases in New York, fir broom rust caused distortions that made hundreds of trees unsaleable.”

This same bulletin also states that, “The affected fir needles on the brooms are stunted and turned downward.”

John Schwandt, US Forest Service: “Broom rust alternates between true firs and chickweeds. Spores from chickweed infect young fir needles. The fungus then spreads into the woody tissues of branches and stems where witch’s brooms form. The yellow color of these brooms is due to yellow-orange fungal structures and spores produced on infected foliage. These spores complete the life cycle by spreading to chickweed. ”

Photos: Anne-marie Ida. Experts Dave Dannaher and Gary Whittenbaugh contributed to this report.

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