Infestations are more frequent in the Southeast, which is also a less prominent grain producer.
In a reversal of an earlier stand, the President said this could harm American grain producers.
China is the world's largest grain producer, with total output reaching a record 456 million tons last year.
A whiskey tax would make western farmers less competitive with eastern grain producers.
Because of the surpluses, grain producers in recent years have been heavily dependent on Government subsidies for any profits.
And some, if not all grain producers are certain to be adversely affected.
The first regulatory step came in 1580, when grain producers were prohibited from selling directly to the market.
Wheat had been the single most profitable crop statewide between 1870 and 1900 as California became one of the largest grain producers in the nation.
The United States and the world's other major grain producers have said famine is not yet a problem.
It became more economical for grain producers to ship to large terminals along the main line.