The cooperatives also cut their forecast of Germany's 2018 winter rapeseed crop to 4.05 million tonnes, down 5.0 percent on the year.

In May, the association had forecast a 2018 wheat harvest of 23.98 million tonnes and a winter rapeseed crop of 4.12 million tonnes.

"The reason is the high temperatures and lack of rain in a large part of Germany in the past weeks," the association said.

Grains in west and south Germany are in a generally good state but plants in north and east Germany have suffered from lack of rain.

"There is sometimes significant levels of dryness damage," it said.

Germany is the European Union's second largest wheat producer after France and in most years the EU's largest grower of rapeseed, Europe's main oilseed for edible oil and biodiesel production.

Barley has especially suffered and in areas with light soils barley is reaching ripeness too quickly before plants are mature, it said.

An early start to Germany's barley harvest could start at the end of June in north Germany if dry and hot weather continues, it said.

"It is not only crops in Germany which are suffering from the dryness, but also in other areas of the Baltic Sea region such as Denmark, south Sweden and Poland," the association said.

The winter barley crop, used mostly for animal feed, will fall 6.6 percent on the year to 8.42 million tonnes, it forecast.

The spring barley crop barley, used for malt and beer production, is still expected to increase by 23.8 percent on the year to 2.26 million tonnes after sowings were expanded.

Germany's grain maize (corn) crop will fall 4.2 percent to 4.35 million tonnes, the association said.