I am having yellow spots appearing on the leaves of my knockout rose plant, one of four together. I feel that they are getting adequate water and fertilization. Please advise.
Yellow Spots on Roses
There can many many reasons for the yellow spots on the foliage/leaves. It can range from an underleaf insect munching on the underside of the leaves. It can be the start of a fungal attack, it can be caused by what is called "spray drift" which is where something sprayed nearby drifts over and gets on the rosebushes foliage. Thus yellow spots appear where the spray droplets caused an irritation to the leaves. It can also be the start of the leaves normal life cycle of dieing and falling off. If the leaves in question are shaded by the other foliage or are lower on the bush, it can just be that the bush does not need them any longer as they are not helping the bush to thrive and survive. I recommend looking closely at the under side of the leaves to see if there are any bugs under there. If there are, you likely need to spray the rosebushes with a good insecticide being sure to get some of the spray up under the leaves. If there are no bugs to be found, I recommend spraying the rosebushes with a fungicide such as one called Green Cure. It is earth friendly and cures alot of fungal problems. Check the soils moisture too with a moisture meter and probe down into the ground as deeply as you can, this will help tell you if the soils moisture is good down towards the root zone. Here is a link to an article for you too: