Problem converting foliage into a static mesh

Hello there i have a problem converting foliage into static mesh. i tried everything. merging it and exporting it. But nothing. the thing is that there is a lot of foliage and my fps drops at 7 and i want to do it static mesh so to not have those drops. But in the converting it converts it like this in the photo. what can i do?

anyone guys, its getting me crazy this issue.