Q. My roses had lots of problems last year. Can I do something now for better looking roses this season?
— Anita Zehnder, Los Osos
A. Many gardeners have a love-hate relationship with roses: They are often our favorite flowers – but they also have the most problems. First, let me recommend the University of California online information on pests and diseases of roses: http://www.ipm.ucdavis.edu/PMG/GARDEN/PLANTS/rose.html. This will help you diagnose the problems you encountered last year. This site describes the long list of possible rose problems and offers remedies.
Locally, our common problems are aphids, rust and black spot. In spring as new leaves develop on roses, aphids will likely attack. Before using insecticides, try a strong jet of water. This will be successful if repeated. The next line of defense would be insecticidal soap. Insecticidal soaps are most effective when they are applied directly to and thoroughly cover the insect. There is no residual activity with soaps, thus limiting harm to beneficial insects. Just as with the strong jet of water, soaps must often be repeated for successful control.
Rust and black spot appear with warmer weather. Both these fungal diseases thrive in damp environments, so roses grown in foggy coastal areas are especially susceptible. On-the-ground watering systems can help avoid them. If you must water with overhead spray (or do water-jetting for aphids), do it early in the day, so that leaves may dry completely. Be aware that anti-fungal sprays sold commercially are most effective when applied to protect the plant. They should be used before symptoms appear.
You can prevent disease-ridden roses by growing resistant varieties adapted to your micro-climate. Before buying new roses, ask your local nursery or neighbors which varieties might thrive locally. In any case, optimal routines of pruning, fertilizing and irrigation should produce bushes that can survive attacks of pests or disease. Some enthusiasts do succeed in growing roses without pesticides, but they acknowledge that they put up with plants that look less than perfect at all times.