The poll echoes results in two other polls last week, one conducted by Forsa for magazine Stern and broadcaster RTL, and another by pollster INSA.

Declining support for the Greens could reduce the chances of a left-leaning "red-red-green" alliance of the Social Democrats (SPD), the far-left Linke party and the Greens after a Sept. 24 election.

The Emnid poll showed Merkel's conservatives adding one percentage point to 36 percent, expanding their lead over the SPD, which remained unchanged at 31 percent. The Social Democrats are junior partners in the current coalition, but hope to unseat Merkel and lead a new government.

The far-left Linke and the anti-immigrant Alternative for Germany remained unchanged at 9 percent.