Blasted blackspot

Q Why is blackspot rife on our roses, despite spraying with RoseClear? JOHN BROWN; PAT WILKINSON, BY EMAIL

A Blackspot is a common problem on roses and the disease starts to infect the foliage in late spring. Fungicides won’t remove an existing infection – they only protect new growth from becoming affected, so it’s best to start spraying early in the year before there are any signs of the disease. The new growth should then come through healthy and clean. It’s also worth taking out some of the centre branches in late winter to open up the centre of the shrub because better air circulation will go some way to preventing the disease. Picking off affected leaves can remove some of the infection but it will weaken the plants.

Q What is ravaging salvia ‘Amistad’ foliage? CHRIS WRIGHT, WEST SUSSEX

A This is damage caused by capsid bugs, an elusive insect that feeds on a plant’s growing tips. As they puncture the tissue, they inject a poison that causes rips and holes in its foliage. The problem is worse in hot, dry weather and they’re common on salvias, fuchsias and willowherbs among others. You could nip out the affected shoots; later growth may be unaffected. Or you could spray with an organic insecticide.

Q Can I treat these brown marks on bergenia leaves? SARAH PETERS, BY EMAIL

A Bergenias are generally problem-free, although vine weevil adults can nibble around the edges of the leaves. I think the brown spots are due to water stress and the high heat in late summer, especially if the plants are in full sun. Keep the plants well watered and they should grow away well in time.