Growing up in Sheffield when it really was rather dirty and boasted some of the worst air pollution in the world, one thing I never saw was ‘Tar Spot’ fungus on sycamore leaves.
Indeed, I only noticed this when I went to Lancaster University as a student and was amazed to see rather unpleasant-looking black growths on otherwise healthy sycamore trees.
The same thing may have been apparent to gardeners keeping prize rose-bushes and noticing how the dreaded ‘Black Spot’ is now much more prevalent. In the 1960s and 1970s, this was something you simply didn’t see around Sheffield.
Across the region folk burnt heavy-duty coal laden with sulphur and tar and the result was pretty appalling.
The reason for the absence of these fungal diseases was that the sulphur content of the atmosphere that acted as a potent fungicide. With the Clean Air Acts and other legislation that have reduced factory-borne and domestic air pollution the levels have dropped
but a consequence is that both Tar Spot and Black Spot have returned. So I guess this is a case of swings and roundabouts.
For gardeners the part solution is to choose your rose bushes from varieties that are Black Spot resistant. In the case of sycamore trees, the fungal infection certainly doesn’t seem to diminish the plant’s vigour, but I wonder how well they might grow in the absence of the disease.
We still have plenty of air pollution but it is very different from the Sheffield smogs of my childhood and bronchitis-inducing, sulphurous fogs that used to hang over a winter walk to school.
The modern pollution tends to be rich in nitrogen compounds (from power-stations and cars) that act as a widespread chemical fertiliser over much of the land. This is turning many wildlife habitats into what we call ‘eutrophic’ i.e. nutrient-rich conditions and this causes problems for many species of wildlife and especially some of our now rare wildflowers.
However, there is some suggestion that the nitrogen oxide levels in atmospheric fallout are now diminished which if true, would be good news indeed.