A local Consulting Rosarian may be able to help identify any issue you have in growing your roses.
It's a good thing to provide a covering of mulch to help maintain the rose bed ground moisture and temperature, as well as to control unwanted weeds. If the mulch has a tendency to compact and cause water runoff, then it needs to be broken up periodically to allow water to penetrate. If not, drip irrigation (or similar) under the mulch may be needed to allow water to reach the plant roots.
Typically roses need "about an inch" of water per week - whether naturally or artificially. The type of soil, drainage, temperature and how much direct sun all play a role in just how much the plants need. Side effects of inadequate water stressing a plant include yellowing of leaves. Besides insect or fungus issues noted below, yellowing most commonly this is caused by either too much or not enough water.
Most, but not all, roses will produce more blossoms if the spent blooms are removed so that energy is not spent on making hips. This will encourage more blooms.
Insecticides/fungicides/any kind of control can be harmful to 'good' insects, hummingbirds, wrens, fishes and humans. Caution should always be a priority in use of any chemical while following the directions carefully. Consideration should be given to applying insect chemical controls only when when a specific threat is present. In general, prevention is the choice in terms of funguses.
Japanese Beetles - primarily devour the blooms but also will eat the leaves - see related article by Larry Meyer.
Spider Mites - love the heat and spread rapidly. Often seen as tiny dark specs on the underside of the leaves, often with tiny spider webs. Can quickly suck all the energy out of a rose (and other plants) and cause leaf drop. If small infestation they can sometimes be controlled by high pressure water to blow them off. If unsuccessful, a miticide specifically targeting them is often the only control.
Aphids - typically small green critters normally found on fresh growth and buds but also on many plants, they can be sprayed off with some success, squished, or controlled with almost any general purpose insecticide - including insecticidal soaps.
Common rose diseases in St. Louis include blackspot, powdery mildew and downy mildew. Each is best prevented by good cultural practices but if those fail there are chemical treatments that can control, if not eradicate, the problem.
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