I started growing lilies about 2 yrs ago, I have both asiatics and orientals. For some reason, my asiatic foliage starts to turn brown, pretty much as soon as, or even slightly before, they bloom. Now, some of them are finished blooming, and the foliage is all brown and dead looking, but only with the asiatics, the orientals still have nice, green foliage. Is this normal for them to die back so soon? Or, does it indicate some kind of fungal/insect problem? They bloomed beautifully, so it doesn't seem to affect the flower quality. I should mention that the asiatics and orientals are planted in the same bed. Thoughts?