The European Union's crop monitoring unit MARS lowered its yield forecast for spring barley and maize due to the negative impact of sustained hot and dry conditions in southern Europe.
The conditions affected large parts of Italy, Hungary, Romania, Bulgaria and Greece, as well as in southern Turkey, MARS said.
Meanwhile, the summer crop yield forecasts in western and central Europe remained positive, benefiting from a slight upwards revision due to higher than average rainfall, it said.
However, the wet weather has also hampered the harvesting of winter and spring cereals, and caused delays to early sowing activities in eastern Germany and in Poland.
"In Finland, the overly wet end of summer is the most recent of a series of unfavourable events that reduced yield expectations in terms of both quantity and quality," MARS added.
The average grain maize yield in this year's EU harvest is expected to reach 7.78 tonnes per hectare (t/ha), down from a projected yield of 7.90 t/ha in August.
That would be 6.5% above last year and 0.3% above the average EU grain maize yield of the past five years, it said.
MARS also cut its forecast for the spring barley yield to 4.23 t/ha, from 4.30 t/ha seen last month, now 5.7% below last year and 2.9% above the 5-year average, while the projected EU sugar beet yield was kept unchanged at 75.0 t/ha.
In August, Strategie Grains lowered forecast for wheat and barley harvests due to adverse weather in the European Union.