Cover the stem with plastic or a mason jar. To cover the stem with plastic, insert two eight-inch (20-cm) sticks or wires into the soil on either side of the stem to prop up the plastic. Cover the pot and stem with a clear plastic bag, and affix the bag to the pot with an elastic or twine. With a mason jar, simply place a large mason jar over the stem.
Roses are flowering perennial plants prized for their beautiful flowers, which are made up of delicate and layered petals. One of the best ways to propagate new roses is to take a cutting from an existing plant and grow it into a whole new rose bush. When you grow roses from a cutting, you cut a stem from a healthy plant and root it in a growing medium so it grows into an independent plant of its own. However, you can also propagate roses by dividing an existing plant, but this requires a little more effort than with cuttings. To propagate by division, you have to dig up an entire rose bush, cut the root system in half, and replant the two halves as separate bushes.
This is a fungus called black spot. Left untreated, it can cause all the leaves on your roses to turn yellow and fall off. It will also affect nearby plants, as it spreads by spores. Remove ALL INFECTED material and throw it away or burn it. Do NOT leave it on the ground as this fungus is very hardy. It can survive winter and travels very easily, even after being removed from the affected plant. Spray your plants regularly (bi-weekly) in the growing season with a good fungicide (I like the Bayer products). You can also add a little bit of dish soap and baking soda to a spray bottle with water and spray the entire plant.
Black Spot: Rose plant leaves with black spots that eventually turn yellow have black spot. This is often caused by water splashing on leaves, especially in rainy weather. Leaves may require a protective fungicide coating, which would start in the summer before leaf spots started until first frost. Thoroughly clean up debris in the fall, and prune out all diseased canes.