Wednesday, July 15, 2015

How Does a Plant Qualify for Noxious Weed Classification? Hoary Alyssum, Berteroa incana

Our star of the day is Berteroa incana (hoary alyssum, berteroa blanche), an introduced invasive species here in North America which is originally native to Eurasia [1]; it is a member of the Brassicaceae (mustard family). US range map here, Canada range map here. This plant is marked as weedy/invasive in the US [2], but is not listed federally as a weed in Canada [3]. Berteroa incana has noxious weed status in Michigan [2], and in Alberta, British Columbia, and Saskatchewan [3].

Berteroa incana inflorescence
I've mentioned a couple of other plants with noxious weed status on this blog: Leucanthemum vulgare, and Alliaria petiolata. So at this point you may be wondering what a plant has to do/be in order to obtain the noxious weed classification.

The answer to this question isn't always entirely straightforward, because there are a number of potential reasons for governments to confer noxious weed status on a plant, and because sometimes plants which exhibit similar traits to legally recognized noxious weeds aren't on the list for a variety of reasons (eg lack of resources, petition for review hasn't been tabled before the assessing body, insufficient scientific data, management concerns, political reasons, economic reasons).

Berteroa incana whole-plant view (in among a rambling pile of other plants)
The nice thing about Berteroa incana for the purposes of this discussion is that it exhibits more than one of the common traits that will lead a plant to be classified as a noxious weed. For example, it used to hold the noxious weed classification in Michigan [4], because it had been implicated in loss of pollinator diversity and therefore constituted a presence disruptive and deleterious to native ecosystem function [5]. It is unclear from my research whether this hypothesis has been disproved or if the plant has since been removed from Minnesota's noxious weed list for other reasons.

This plant's noxious weed status in Michigan must be attributable to agricultural or environmental undesirability, as these are the criteria listed by the state for plants to qualify for the noxious weed list [6]. It is possible that Berteroa incana was assessed as both; the list provides no further detail.

Berteroa incana inflorescence
Berteroa incana's noxious weed status in Alberta and British Columbia is explicitly outlined as being due to its toxicity to horses [7,8], and in British Columbia also because it interferes with alfalfa crop quality [8], by invading alfalfa fields and competing with the forage plant; it also ends up in the hay and is considerably less nutrient-rich than alfalfa, thereby reducing the nutritious value of the fodder produced.

Phyciodes cocyta collecting nectar from Berteroa incana (photo posted before on this post)
So a plant can end up on a noxious weed registry because it is particularly deleterious to ecosystem function, or because it is undesirable from an agricultural or environmental standpoint. If I have a reliable source on the matter, I will generally indicate why a particular plant is listed as a noxious weed. But if I don't, it is one of these reasons (and I couldn't find out which).

As for what to do about this plant... well, small populations can simply be pulled by hand [8], or in some places and contexts it may be appropriate to treat with an herbicide (2,4-D, dicamba, or glyphosate) [4,8].

I am remembering a visit I made to Toronto a few years back in August where I lost my voice because of the smog. The same thing is happening now with all this heat and traffic in Montreal, only it's not a visit; I'm stuck here until the end of the month and I'm losing my voice fast (I'm already at the stage where I can no longer hum). I had forgotten how hard it can be to breathe in a large city in summer...

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