You will need some modelling program to create meshes yes (3ds max, Blender, Maya etc). A texture alone can’t really be used for many thing other than landscaping or existing geometry. You can also use BSPs (http://blog.digitaltutors.com/unreal-engine-4-bsp-geometry/) but that’s more suitable for buildings and structures, not even sure if it can be used for foliage. There’s plenty of programs which allow you to generate models like trees, for example Speedtree and Arboro, though that kind of software tends to cater more to artists already familiar with stuff like this.
If it’s just a plane / flat mesh you want, I can easily send you an fbx based on your texture, that shouldn’t take more than a few minutes, just send me your textures and I’ll map them onto a plane 
You can then import it into UE and apply your material to it. But eventually you’ll have to either create your own assets or purchase items from for example the marketplace. 