Combating Rose Pests and Disease
If you notice your roses seem to be struggling, it is a good idea to clean the area around them - remove fallen detritus, leaves, etc. It is helpful to prune roses as well. While working at these tasks, inspect the roses for signs of pests or disease - a magnifying glass is essential as most pests, excepting Japanese beetles, are too small to be readily seen by the eye. Typical rose pests include aphids, rose chafers, Japanese beetles, leafhoppers, thrips, mites, slugs and sawflies.
Japanese beetles with their hard shells are typically easy to spot due to their bright coloration. The best means to organically get rid of them is just to pick them off by hand, one by one, and give them a squash. Drowning them will also do the trick. To chemically destroy these pests, spray with rose-friendly insecticide.
Aphids may be brown, red or green in color. They create unsightly problems for roses. As they suck at the rose juices, they coat unopened buds and other areas of the rose with honeydew that uniformly attracts ant colonies to dine on the juice therein. Aphid attacks also result in malformed flowers and leaves - an altogether unhealthy and unattractive appearance. To organically give them a taste of their own medicine, import beneficial insects that like to munch these aphids. A blast from the garden hose may rid them as well. The other option is to spray rose-friendly insecticide.
Spider mites are red or yellow insects that suck rose leaves resulting in loss of color and finally just dropping off the plant. Hose spray will usually dislodge them from their favorite meal, but introducing other insects to eat them is a more permanent solution. To synthetically get rid of them, spray with miticide or rose-friendly insecticide.
A variety of waxy-shelled insects termed as scale suck at rose juices that results in growth impairment. Lacewings are a natural predator. The other organic option is to remove the affected parts of the plant and destroy. Insecticide labeled for use on roses is the chemical option.
Rust is a common disease incurred by roses. Symptoms of rust show on the leaves - orange patches and blotches. To organically eliminate rust, remove and destroy leaves with the telltale spots. Then, be sure watering is done only at the base of the plant. Pruning may help air to better circulate around the plant. Synthetic controls include spraying the dormant plant with lime sulfur and the active plant with neem.
Blackspot results in black circles on the leaves which gradually turn yellow and fall. Leaf edges may also fringe. All plant parts affected must be removed and destroyed. To synthetically control, spray with neem or copper sulfate fungicide.
Finally, rose mildew results in powdery white coating of leaves. To combat organically, remove and destroy the affected parts. Be sure to spray the plant weekly with the hose. Synthetically, a dose of neem will also do the trick.
If possible, prevention is the best method to control pests and disease. Tamping down on weeds and layering mulch around your roses will go along way to discouraging serious problems. Prompt removal of pests and diseased parts and careful pruning are also top priorities for keeping roses healthy.