Unless one is a pro with roses it isn’t uncommon to make a rose bed of many different kinds and then treat them all the same. This is a big mistake…roses are each individual in needs, issues, and output.
It is just as uncommon to find one particular rose with many different issues.
They each seem to have one or two weaknesses that can and often do come calling .
For example…Grandifloria’s are prone to Aphid infestation–look for tiny, green, brown, or white, soft bodied insects-usually on the backs of the leaves.
Sometimes a good spraying with the water hose will destroy these critters and if not, wash gently with a safe insecticidal soap spray…continue this spraying until they are gone.
( another, more natural way to eliminate Aphids is to make sure you have Ladybugs in your garden…they dine constantly on Aphids, and can consume thousands in a just a few hours.) Ladybugs are totally harmless to garden plants…a good bug in every way.
Floribunda’s seem to be a target for Botrytis blight…a fungal disease that appears as a gray growth on buds. Flowers that are affected will fall apart, rather than open normally.
Pick off and destroy affected blooms and spray with a fungicide in severe cases.
( A good strong compost tea will also control this blight if started early and repeated long enough.)
Hybrid Tea’s are prone to rust and Japanese beetle attacks.
Rust will appear as small brown powdery spots that spread across the leaves. They will eventually turn yellow and fall off. Remove infected leaves and destroy…never drop any infected leaves on the ground under your rose bushes, this will allow the disease to infect the soil and back into the plant. I find a mixture of 1 part white vinegar and 4 parts water will get rid of rust.
Japanese beetles are tricky…they don’t succumb to any known combative…a good hard spraying with the water hose will drive them away, kill some, and if done often enough will discourage them from hanging around.
Don’t use the bags on the market that draws them in and traps them…they love the mixture in the bags and will come from far away to dine on it-so you are just inviting more than you might have otherwise.
You can easily hand pick or knock them off, into a can of oil early in the morning or late in the day…they are sluggish at these times….they can’t get out of the oil and will die.
Do not put these in your compost…they stink and the oil will contaminate your mix.
A good point to always practice…good, clean, chemical free soil is the best guard against any disease in any garden. Bad insects, fungus,
etc., don’t like or hang out in good soil. It is the one most important step to having a garden free of problems.