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I have a big big problem, up here in Western Washington...

My outdoor cactus beds are constantly being overrun with quackgrass overrunning cactus beds. Mostly Opuntiads, but also some Echinocereus and semps.

Will herbicides designed to target weedy grasses such as GrassBGone be safe to destroy grass while leaving cactus alone?

Also, will Casoron germination inhibitor harm existing cactus while mitigating invasion of dandelions/etc?

Thank you so much.

Ed J
the CACTOMAN

I know I'm not directly answering your questions. I'm not 100% sure as I don't usually use chemical herbicides. But, can you paint the herbicide on the target grass rather than spraying?

Bigger question: can you edge the beds with a root/runner barrier to prevent the beds getting overrun by the grasses?

We used to use a pre emergent herbicide (Oxadiazon granulas) for pots in the nursery. It's designed to kill germinating seeds only and did not affect the trees. As for the grass in the beds, you can safely spray glyphosate around the cacti as long as you don't wet the plants too much. Their waxy coating prevents the chemical from entering. I once sprayed glyphosate right over the top of a heavily weed infested planting of Senecio serpens and it worked perfectly without harming the senecio in any way. Try to find a Round Up which does not have powerful wetting agents added to it.

Quackgrass is a real pain, it will come back. Germination inhibitors won't help, since it spreads by rhizomes. However, if you put down a deep mulch, the rhizomes will run just under the mulch and can be pulled out easily. I found wood chips worked well for this, I'm sure gravel would do the same. After you get the stuff killed out of the beds, a band of deep gravel around the outside of the beds would provide a defense against its return. I doubt that barrier edging would be successful, the rhizomes can go quite deep, and they will find any crack.

Don't put down landscape fabric, the rhizomes will run under it and you won't be able to pull them out.

I know that Roundup kills it very effectively so you only need not to spray but use small brush and put small amount of Roundup on grass stems and leaves. It will kill all rhizomes also.

What the Roundup web site says about that: "Thanks to this plant's hardy nature and extensive root system, it may require a second application to wipe it out completely."

I think they're being over-optimistic.

According to my own experience it's very effective with monocots.