You may decide to just let nature take its course in which case your roses will suffer some damage and may be weaker next year. Some gardeners, however, will decide to help nature along with a little gentle intervention. Here are suggestions for limiting pest damage while not resorting to harsh chemicals.
What you'll need:
1 gallon garden sprayer; a smaller capacity sprayer will do if you have only a few rose bushes
fresh insecticidal soap concentrate; not household liquid soap!
neem oil or EcoPCO WPX botanical insecticide
Milky Spore microbial insecticide for soil dwelling white grubs
a fungicide that contains copper or sulfur, which may or may not be combined with soap
Use the garden sprayer to apply all of the garden chemicals. Insecticidal soap is a highly refined liquid soap that when used properly won't harm your plants. It is very effective against aphids, spider mites and other soft-bodied insect and mite pests. Don't use other household soaps, as some suggest, as these may actually damage or even kill plants.
Neem oil and EcoPCO WPX are both derived from natural plant oils and are effective against pests that chew on leaves like Japanese beetles. Both garden chemicals must be reapplied frequently (see label instructions), however, because they have limited residual activity (the time that an insecticide remains effective after application).
Fungicides inhibit growth of the fungi, or molds, that cause disease in plants. Black spot fungus is a common disease of roses and should be managed with copper or sulfur sprays.
Aphids are small insects that literally suck the life out of plants. They live in colonies on stems and leaves often covered by a sticky liquid "honeydew". Honeydew attracts ants and yellowjacket wasps. Aphids can be dark in color or light, greenish or yellow; "greenfly" is one common name, "plantlice" is another. Because aphid colonies grow so quickly they are often the rose grower's most important insect pest year after year.
Aphids are easy to control but most gardeners simply don't notice them until colonies are large and significant aesthetic damage has already been done. If damage is allowed to continue your rose bushes will become weak and won't be able to produce quality flowers.
Easy Aphid Control on Rose Bushes
As soon as you notice aphid colonies or honeydew do the following: wet entire plant with water from a garden hose; mix up a 2 percent solution of insecticidal soap (2 oz. / gallon); thoroughly spray entire plant with soap solution being careful to make contact with the undersides of leaves; wait 30 minutes then rinse plant with water from the garden hose. Repeat this procedure whenever you notice aphid colonies. The sooner you stop the infestation the better! A bonus - this treatment will also control spider mites just as well!
Japanese beetles [picture of Japanese beetle] feed on the foliage of rose and many other landscape plants. Japanese beetle larvae, a type of white grub, also feed on roots causing twice the injury. While Japanese beetle does not occur everywhere, where it does occur it is a serious garden pest.
Protect Roots and Foliage from Beetle Damage!
Japanese beetles can be hand-picked off plants and dropped into a container of soapy water. Beetles can also be prevented from damaging foliage with timely applications of either neem oil or EcoPCO WPX botanical oil insecticide. Either insecticide will effectively stop feeding adult beetles from damaging your bushes.
Japanese beetle and other white grub larvae can be safely eliminated from the soil with a microbial (bacterial) insecticide called Milky Spore that targets only certain soil dwelling insect pests. Milky Spore bacteria may take several years to become completely effective so be diligent about adult beetle control as outlined above until then.