No, if the price of land decreases, it only discourages people from selling if they think that the price will come back some time in the future. A permanent tax change won't make people think that.

More: If the tax rate has gone up enough that the price has gone down, then if I hold it, I'm also having to pay the higher taxes year after year. That's going to encourage selling, not discourage it.

I don't like Georgism for other reasons, but I think that part will work as advertised.