I'm not so sure this argument is as viable as it appears at first glance. The author points mostly to the rise in corn prices since it is linked to many other food staples. While he correctly points out that the cost increase is due to the rise in demand of corn for ethenol products, he appears to ignore the basic market process. The rise in price is due to the rise in demand: as demand increases prices goes up and as demand decreases, prices go down. Right now, we've had a spike in demand for corn that does not correspond with production. I would think that if the demand continues, corn growers will increase their production thereby decreasing the overall price.

As for using food as a weapon, I see international law concerns. Although food is certainly used by military forces, and international law does account for dual use when it comes to targeting (e.g. a bridge could be a lawful target since it allows an enemy to deploy forces despite the fact it is also used by civilians to take food to market), I doubt it would go this far. I don't really see a difference between carpet bombing a city and freezing food shipments to that city. The end result is the same: the targeting of the population as a whole by lethal means. But maybe I'm wrong. I'd be willing to consider arguments to the contrary.