Selecting a disease-resistant rose is the single most effective way to avoid problems and the need for chemicals. You might start by considering some of the old rose varieties, many of which have natural disease resistance. You can also look to many of the modern roses, which are now being bred for improved disease resistance. Hybrid teas are notoriously disease-prone, and seem to lure every insect pest from miles around. They can be difficult to grow without an arsenal of chemical dusts and sprays.
i believe the key to rooting a plant cutting in water is to keep it warm, but not sunburnt in strong full sun. my african violets all seem to root better in water than perlite or soil! the water level is determined by how the mother plant takes water--roses can take lots of water, so root in 3-5" of water. succulents dont like to stand in water, so root in 1/8" of water standing with only the base touching the water.