Pre-emergent could work for the gravel area's. Use Roundup to kill weeds present currently and then apply the pre-emergent. Granular varieties require water to dissolve and form the protective barrier. Kills germinating seeds before they can sprout.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)