Vicki's StoryA Microscopic Fungus --
Black spots on roses appear mainly due to high humidity, and watering late in the day, which doesn't give the leaves a chance to dry.
Although black spots can be transferred to roses for a number of reasons, via the air, the moist conditions are a perfect storm.
Prevention is the best to deal with this.
NOTE: THE DORMANT OIL USED FOR INSECT PREVENTION SHOULD BE DONE IN EARLY SPRING, BEFORE BUDDING/LEAVES APPEAR
SEE BELOW FOR SOME TIPS FOR DORMANT OIL - AND TO MAKE YOUR OWN.
THE RECIPE DIRECTLY BELOW IS FOR BLACK SPOT PREVENTION ON ROSE LEAVES
1Mix all ingredients in a clean bowl or bucket, mix well.
Pour desired amount in a spray bottle. In the morning or early part of day spray your rose bushes genereously. It is best to do this in the early part of spring to also prevent the early pests.
2Another preventative for Black Spots on Roses is "Milk".
Put in a spray bottle, and spray leaves top and bottom - in morning or early part of day.
3Dormant oils stick to the insects and suffocate them by clogging the pores they breathe through.
Petroleum Based -
Most dormant oils that are commercially sold are refined from petroleum oil and have an emulsifier so they can mix with water. These are known as mineral oils.
WHY DORMAN OIL?
The oils work best when the insects are just emerging from their dormancy period early in the spring.
Dormant oil is a liquid substance that is sprayed onto trees when they have no leaves, thus the term dormant. It acts as a fungicide and pest control agent to prevent damage to the buds that will open in the spring.
4SPRAY WHEN OUTSIDE TEMPERATURE IS ABOVE 50 deg. for a couple of days.
Pour 1 cup of vegetable oil into the garden sprayer, followed by 2 tbsp. of liquid dish soap.
Add 1 gallon of warm water to the sprayer tank or bottle. Shake well and saturate trees, exposed bark, branches - before budding in the spring.
Read more: How to Make Dormant Oil | eHow.com ehow.com/how_8603771_make-dormant-oi...