Herbicide to kill orchids?

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Does anybody know of a good herbicide for invasive orchids? Years ago Dow made a product called Dowpon that supposedly killed monocots but left dicots unharmed. It was sold to kill grass invading flower beds and crop fields. I haven't seen it for a while, so I don't know whether something like that is still manufactured and sold.

I'm asking because in late fall 2013 I planted a Thelymitra azurea in a wash that runs through my property. This is a winter-growing, summer-dormant plant, and I already grow a lot of bulbs like that. They do really well during our cool winter with occasional frost, and I hoped the Thelymitra would likewise do well. During the winter this area is frequently damp. The plant did really well, growing and blooming in early 2014, and it set seed. Unfortunately, before I could harvest the pod, it split, and the seed blew away.

Well, the following fall 2014, among the grass that normally sprouts there, I saw something new. I'm supposed to remove the winter annual grass from the wash per the homeowner's association, but I thought I might have Thelymitra seedlings. So, I hand-weeded the grass and let the plants grow. Indeed, they are Thelymitra. But they didn't bloom in early 2015; I guess they weren't mature enough. I kept talking to neighbors about wanting to keep them, and nobody filed a complaint.

Last fall, 2015, they again sprouted. There is now a large patch of them, in flower. I think they look really nice. But, somebody has filed a complaint at the homeowner's association, because I am allowing unsightly weeds to grow on my property. I have 2 weeks to remove them.

I've tried hand-weeding, but the soil is very rocky, so that is extremely time-consuming. That is why I'm asking about herbicides that will kill orchids. I'd like something that will kill all of them but not harm the nearby desert trees. Anybody have suggestions?

Thanks.