How do I stop black spot on roses without spraying constantly?

Black spot, Diplocarpon rosae, needs leaf surfaces to stay wet for about seven hours to infect. Almost everything that works is about breaking that condition rather than about fungicide.

Start with variety, because it does more than any treatment. Modern shrub roses bred for disease resistance — many of the Rugosa hybrids, and a good number of the David Austin and Kordes introductions — carry genuine resistance, while many older hybrid teas are chronically susceptible in a damp climate. Replacing a plant that defoliates every August is more effective than spraying it every year.

Then manage airflow and water. Space plants so air moves between them, prune to an open centre so the bush dries after rain, and water at the base early in the day rather than over the foliage in the evening. Mulch generously, because the spores overwinter on fallen leaves and in the top layer of soil and splash back up onto new growth in spring rain.

Sanitation matters more than people expect. Collect and bin fallen leaves through the season — do not compost them. At winter pruning, strip any remaining leaves off the plant and clear the ground beneath completely. That single autumn clean-up measurably reduces the following year's infection.

Feed for resilience rather than for size. Excess nitrogen produces soft lush growth that infects readily; a balanced feed with adequate potassium produces tougher tissue.

If you do spray, timing beats frequency: preventative applications from early leaf-out, repeated after heavy rain, work far better than reacting once spots appear. By the time you see spots the infection happened two weeks ago.