Black spot on Roses is a disease that can infect roses during wet warm weather. Black spot actually causes black spots and yellowing on the rose leaves.
Very seldom does black spot kill your roses, but it can make all the leaves fall off.
Chop up the 10 healthy tomato leaves into small pieces. Put the chopped up leaves and onions in a bowl and pour the rubbing alcohol over them. Mix well.
Let this mixture sit overnight and steep.
Wrap the cotton batting around your chopstick to make a large Q-tip. You want to make it large enough to let you apply the mixture easily, but not too large that you won't be able to see what you are doing.
The next morning, you will want to remove any leaves that all ready have black spot. Check them over carefully. Once all the black spot leaves are gone, you will want to dip your 'swab' into the tomato and onion mixture you made the night before. Wipe this swab over the entire rose plant. This includes the tops and undersides of ALL leaves.
Depending on the number of rose plants you have, you may have to make more of this mixture. This recipe yields about 1/2 cup of tonic.