By Alexander Ratz and John Irish WEISSENHAUS, Germany (Reuters) -Group of Seven foreign ministers vowed on Saturday to reinforce Russia’s economic and political isolation, continue supplying weapons to Ukraine and tackle what Germany’s foreign minister described as a “wheat war” being waged by Moscow. After meeting in the Baltic Sea resort of Weissenhaus, senior diplomats from Britain, Canada, Germany, France, Italy, Japan, the United States and the European Union also pledged to continue their military and defence assistance for “as long as necessary”. They would also tackle what they called …