Can you re-apply a pre-emergent, once shrub roses are blooming? Have black/brown spots on leaves and leaves look like something is eating on them.
Certified GKH Gardening Expert
I would give the rosebushes a treatment of Bayer Tree and Shrub Granules per the label instructions for Ornamentals/Roses. It is a systemic disease control product and has some food in it too so that it helps strengthen the bush to help fight the disease attack. A pre-emergent usually refers to an herbicide which is not what is wanted here, so I am assuming that you mean a systemic. Yes you can reapply systemics once blooming has started. If the rosebushes turn out to have black spot fungus attacking them, you may need to spray them with a product called Mancozeb, it is available on Amazon.com and will stop most black spot attacks in their tracks.