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Tuesday, July 20, 2010

Bad, Bad Purple Plant

spotted knapweed

At least in the eastern US, the bad, bad plant is the Spotted Knapweed. This is the answer to the post Purple in the Fields - Pick the Bad Plant

It was interesting to me that each of the plants had at least one guess. Let me tell you about the others first. The Big Bluestem is a native prairie grass that is actually very desirable. You might not want it in a garden, but I'm SO glad that there is a big patch of it filling in the field. It's tall- 6-7 feet.

The mistflower is native to the US. It does not seem to be a pest in our area. Actually, I've only seen it a couple of places other than in my field. I'm amazed at how happy it seems here. I transplanted some to the east side of my house because it seems able to take the hot morning sun bouncing off the house.

Most interesting was Julia's response. She really knows plants, but I think each of us would be lost in the other's home space. She identified it as Himalayan Blackberry, a genuine invasive pest in the west. I don't think we have that one here yet. This is probably Rubus hispidus, although they hybridize.

So we are left with the Spotted Knapweed. Betchai call it right. She's looking like a bit of a plant expert herself with two correct IDs in the past week! Why is this such a bad plant? There are several reasons.

1. It is not native to the US, but to Eastern Europe. When plants are moved to spaces where they were previously unknown they tend to either die out or become aggressive. This is because all of the natural checks and balances don't usually come with them, such as insects or animals that eat them.
2. It has a long tap root that outcompetes other plants for water. Anyone who has tried to manually control this plant knows how difficult it is to pull up. You really can't get it all up unless the ground is moist.
3. It produces a LOT of seeds. Once the spotted knapweed gets started in an area it will soon be found everywhere.
4. It tends to be passed over by grazing animals. It is less palatable than many other plants. Cows, deer, rabbits, etc will leave the spotted knapweed and preferentially eat other plants, leaving the knapweed to propogate.
5. There is some evidence that it is allelopathic. This means that it can exude chemicals that inhibit the growth of other plants in the vicinity.

Just about the only way to eliminate this plant is to get an army of people to pull plants on a regular basis. This is a never-ending job, so except for perhaps small areas, it can't be eradicated.

My point of this post is to remind everyone that there are invasive plants where you live! Learn how to recognize a couple of them, and do what you can to prevent their spread.


Dennis the Vizsla said...

It sounds like Purple Loosestrife's ne'er-do-well cousin.

Duxbury Ramblers said...

Alien plants - most are beautiful in their native places, then they escape, we have our problem aliens the main one at the moment is Himalayan Balsam lovely plant and the bees love it, sadly it takes over large areas in no time at all. I am sure some natural remedy will come along and bring it under control, along with our help to contain it. Our Common Knapweed C. nigra is a magnet for all sorts of insects, moths etc. Glad you enjoyed the young mink video, they have been a pest since the mass release in the late 90s but as you say very cute.

Ann said...

I guess I shouldn't have been fooled by this ones beauty

betchai said...

i learned about this plant in the trails here, oftentimes, at the trailhead they have pictures of non-native plants and what we could help to prevent them from totally crowding out the native species. thanks for sharing the more detailed explanation what makes them a bad plant.

Ratty said...

I noticed this plant growing all over at Island Lake park recently. I thought they looked really nice growing in the tall grass. It's a shame to read they are not a good plant to see there. Beautiful but deadly.

Sharkbytes said...

Dennis- I think the loosestrife is worse. If it is more than 3 years old you need dynamite to remove it. I spent quite a few years as the primary remover of that plant from a wetland at a Bot Garden. Horrid stuff.

Carole- mink a pest? mass release? interesting. Any animal can be a problem in big numbers. The deer here are awful, truth be told.

Ann- Maybe I'll dig out a picture of it's sister plant, and you can see that this one is the homely child (that not what makes it bad though)

betchai- it makes a lot more sense when we understand why they cause problems, for sure.

Ratty- yup... lots of times the bad ones also turn out to be pretty too.

RNSANE said...

Plants can definitely become pests. I think about the kudzu in the South...I think it was brought in from China but it is definitely a pest when it overgrows plants and trees and shuts out their light. It takes over whole landscapes.

wiseacre said...

Spotted Knapweed is hard to ignore around here - it's everywhere that's sunny and dry.

Purple Loosestrife is in full bloom - huge colonies at the northern end of the county in the wet meadows. What makes it so invasive is the seed. It's seeds have a longer life span than most people. All it takes is the soil to be disturbed and it will germinate.

Sharkbytes said...

Carmen- I think the japanese knotweed is going to be the kudzu of the north. It's really awful.

Wiseacre- the loosestrife is really something. I played a minor part in the first release of the Galerucella beetles in Michigan. It takes a lot of years for them to make a difference, but it has finally helped in that original release site.

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