The issue is the opacity.
Everything that gets reduced by the engine ‘suffers’ due to the pixel squishing that mips cause onto the transparency masks.
In this case, disabling mips isnt an option. You are far to far from the scene to even be rendering the plants.
If you need aerial view, simply disable the instances and replace the color of the field via material.
Alternatively, from upright views within the field, just disable the opacity masks after 200m or so from view - you can do this via LOD by creating a different LOD mesh with a different material like you normally do for foliage.
That alone will remove the seemingly white zones.
The other thing is that your asset is wrong.
The image for the grain should not have a white background.
If it didn’t, then there wouldnt be any white areas showing up anywhere.