Hungary and Romania have joined the list, from the US to Ukraine to Zimbabwe, whose corn has been damaged by dry weather, with yields now expected to fall roughly one-quarter from last year thanks to "profound drought".

Romania's agriculture minister, Daniel Constantin, warned on Friday that while the country's wheat harvest would not end up "alarmingly" lower than last year, its spring-sown corn and sunflower crops were being threatened by high temperatures and a lack of rainfall.

"We're going through a profound drought right now, which risks damaging the spring crops, especially corn and sunflower," Mr Constantin said.

"If it doesn't rain in the following period, we might register pretty big losses."

'Heat affecting pollination'

Indeed, according to Jaime Nolan Miralles, commodity risk manager at broker FCStone, "general consensus is that up to 1 tonne per hectare has been shaved off expected corn yields versus the average 4 tonnes per hectare seen last year".

"The problems you are hearing about in the US, of heat affecting pollination, are happening in Romania too," Mr Nolan told Agrimoney.com.

The country, the European Union's second largest corn producer, after France, was looking at a 2m-tonne drop in corn output from last year, when the harvest came in at 10.5m tonnes according to US Department of Agriculture estimates.

And Bulgaria and Hungary were facing crop damage to dryness too, taking total corn losses in the area to 3.5m tonnes.

"If you are working with a world balance sheet already looking tight, the disappearance of another 3m tonnes or so is another factor to be considered," he said.

Silver lining?

However, EU corn hopes received some consolation on Friday when France Agrimer revealed that the French crop, pegged by the USDA at 15.5m tonnes had improved in condition in the week to July 16 by two points, to 75%, rated in "good" or "excellent" condition.

The improvement reflects the rains which, along with slow crop development following a cool early summer, has dramatically delayed the soft wheat harvest, with just 9% in the barn, up six points in the week, but below a figure of 60% a year ago.

In Romania, while the hot weather came in time to lower wheat tonnage hopes, it at least allowed a speedy harvest, which according to Mr Nolan realised "smaller yields but greater quality".

Quality wheat is attracting an increasing premium in Europe, given rain setbacks to French and UK crops and, to a certain extent, Germany's too.