Field Overun with 'Spotted Knapweed"

Markus Antonius · 21-08-2022 11:37PM #1

Noticed a few of these growing in one section of the field last year and didn't think much of them as I didn't know what they were:

http://www.wildflowersofireland.net/plant_detail.php?id_flower=140

After searching for ages, I found that they are called "Spotted Knapweed" and this year have completely taken over the whole field, killing the grass growth altogether.

Luckily I topped them back in April as the few that I missed are now flowering. I've noticed that the leafy base is regrowing so figured now would be a good time to spray them.

Has anyone dealt with these before? Any recommendations for treatment, sprays etc welcome

Base price · 22-08-2022 12:15AM

Do you have a photo of the ones that are now flowering in your field so they can be independently identified. The only reason that I'm asking is cause the photo you posted is from the Wildflowers of Ireland website.

Birdnuts · 22-08-2022 01:42AM

Have them on some of my fields nearest the shore - never caused much bother(stock will happily graze them) and they seem to support alot of pollinators. AFAIK they have no effect on grass growth either

Markus Antonius · 22-08-2022 12:35PM

https://www.boards.ie/discussion/comment/119503590#Comment_119503590

I never have my phone on me when I'm in the fields but will take a pic the next time. They look identical to that picture though. The pink flower has only come out in the last two weeks or so.

https://www.boards.ie/discussion/comment/119503736#Comment_119503736

I was the same but they have completely overun the field now and the cattle won't go near them. The leafy base takes up a lot of real estate and have stunted the grass growth.

Danzy · 22-08-2022 12:42PM

https://www.boards.ie/discussion/comment/119504930#Comment_119504930

There isn't much growth for grass now, not here anyway. Grass is stunted in much of the country.

Top it before flowers are too established and it seeds.

It's a perennial but it isn't robust and topping will do it.

Markus Antonius · 22-08-2022 01:04PM

https://www.boards.ie/discussion/comment/119504956#Comment_119504956

Good to know thanks.

The topping I did back in april or so did a great job but on pulling them up I've noticed the roots are sprouting new stems and the leafy base as seen in the picture has returned.

A quick look online recommends 'Tordon' (chemical name: Picloram), which appears effective at giving 4 years of control with minimal effect on grass. Now might be a good time while they are trying to recover.

One note I read online that is putting the fear in me is that the microscopic seeds stick to tractor tyres and spread to other fields this way.

Danzy · 22-08-2022 01:37PM

https://www.boards.ie/discussion/comment/119505052#Comment_119505052

Is it a lot of cocksfoot or Timothy in the field z it tends to grow better with them.

Markus Antonius · 22-08-2022 02:23PM

https://www.boards.ie/discussion/comment/119505229#Comment_119505229

Timothy yes. The field is surrounded by bog too so not sure if this has an influence. Might thrive in acidic conditions.

I badly need to send off soil samples for all my fields to see whats going on.

Danzy · 22-08-2022 02:28PM

https://www.boards.ie/discussion/comment/119505474#Comment_119505474

It grows in every type of soil. Its great for breaking hard pans and bringing up minerals from deep

Not much good though if it is all that is there

If I had to guess I'd say your grass is drought struck like mine, the knapweed with such a deep route is going deeper and thriving.

Top immediately longer it goes on seed will develop. It will flower into September

Field Overun with 'Spotted Knapweed"

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