Black spot

Diplocarpon rosae

also called rose black spot

Rounded black or purple blotches with feathery edges on rose leaves, the leaf yellowing around them and dropping early.

Fungus Serious Rain splashSpread in waterAirborne spores Spreads to neighbors

What you'll see

Rounded black or dark purple spots with irregular, feathery, radiating margins.
The leaf tissue around each spot yellows, and badly spotted leaves fall prematurely.
Spots begin on the lower, older leaves and spread up the bush through the season.
Small black or purple blotches may also appear on young green stems.
Repeated defoliation leaves the plant weak, with poor flowering and dieback.

Why it happens

The most damaging fungal disease of roses. It survives winter on fallen infected leaves and on marks left on the stems, and its spores are splashed up onto new foliage in spring, where they need continuous leaf wetness to infect.

Warm, wet springs and summers favor it, and it thrives where leaves stay wet for hours through rain, dew or overhead watering, especially on crowded plants with poor air movement.

Treating it

Pick off and destroy spotted leaves, and rake up and bin all fallen ones — do not compost them.
Prune out any marked stems in the dormant season to remove the overwintering fungus.
Water at the base and avoid wetting the foliage.
Feed and mulch to keep the plant vigorous enough to push out fresh healthy growth.
On susceptible roses an approved fungicide, begun as the leaves open and repeated, gives good control.

Keeping it away

Choose rose varieties bred for black spot resistance.
Clear all fallen leaves each autumn and mulch over the ground to bury lingering spores.
Prune for an open center so air moves freely and leaves dry quickly.
Space roses well and avoid overhead watering.
Keep plants well fed and watered so they can outgrow minor infection.

Who gets it

Roses of all kinds, with old shrub and species roses varying widely in how badly they suffer.