Millions of hectares of crops in the US have been destroyed by a massive storm that swept across the midwest on Monday.

In Iowa alone, an estimated 4m hectares of corn has been flattened, one-third of the state’s total acreage of corn. A state of emergency was declared across many of the state's counties.

The storm was classified as a 'derecho', which is a long storm front similar to a hurricane, but without an eye, or centre point. The storm quickly moved almost 800 miles from South Dakota, west and eventually southwards through the heart of the midwest corn belt, taking in Wisconsin, Indiana and Iowa.

Barn damage

In addition, farmers all over the region are reporting that barns and grain stores have been damaged.

Some commentators have noted that many of the stores were empty, and are wondering if USDA estimates of carry-over stocks in the region, and across the country, have been overestimated.

With a month to go to the harvest of corn (maize), it is still too early to say if the crop will be salvable, but such an event has the capacity to change sentiment around the marketplace. That sentiment is still pushing prices downwards, with expectations of a bumper harvest predominating. The crop predictions are for about 15bn bushels of corn, which would be the second-highest ever crop. Corn futures on Wednesday were down for for both September and December.