Burclover in kikuyu grass

I asked Ortho if they had any pre-emergent weed killer that would work on a heavy infestation of burclover (and other weeds with painful pointy seeds) in my "lawn," and they said no. The 'agricultural extension' people never answered my email.
I'm not going for the House Beautiful look, which would be impossible anyway, I just want to get rid of stuff that hurts when I walk barefoot. I'm willing to kill every seed in this 20x50 area, but I don't know what to use and when (SoCal) to use it. Home Depot and OSH are not knowledgeable.
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