Tom's Blog

Monday, April 13, 2015

Good time to spray early perennial weeds

Catnip (Nepeta cataria). Easy to spray
since there is nothing else green nearby
Many perennial weeds come up early, since they overwinter as dormant buds. Right now weeds such as catnip, motherwort, reed canary grass, smooth brome grass, and Canada thistle are already visible, and are lush enough that they can be sprayed. The best herbicide is glyphosate (used at 2%), since it has no soil residual.

We used to think that we could eradicate these perennial weeds by pulling or digging, but soon discovered that this did not work. The reason is that these weeds have extensive root systems and therefore resprout. You can't get all the plant by pulling or digging!

I strongly recommend using glyphosate at this time of year, because most of the ground is still bare. Since glyphosate is inactivated by soil particles, it has no effect on the soil itself. Anything green will be killed, but anything still underground will not be.

However, timing is critical. By next week lots of "good" species will be up, so it is important to be able to recognize what you are spraying. Good plants to watch out for (and might already be up in sunnier areas) include (among others) golden Alexanders, shooting star, native thistles, Trillium, and columbine.


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