Aid for ailing acer Q

My acer is suffering from all sorts of problems. What’s attacking it? Why are leaves yellowing on potted agapanthus? Q Phalaris grass is getting out of control, how can I curb it?

AThe brown, curling leaves are likely to be caused by sun or wind damage. Acers need shelter to grow well and it looks like your tree is planted in a dry or windy spot. So, move it in winter if you can and feed it to boost its general health.

The red dots (right) are caused by gall mite, and I’m afraid there’s no treatment available. It usually doesn’t harm the tree much although the leaves will fall prematurely.

The eye-like markings on the trunk are caused by scale insects. These suck sap from the stems and branches and, as they mature, the females lift and release young in a mass of waxy fluff. They’re a more serious problem for your tree. Start by scraping off the scale insects and egg masses with a plastic plant label, then power wash its branches. If this doesn’t help, spray with Provanto Ultimate Bug Killer or BugClear Ultra (both approx £5-£10 for 1L spray).

AI suspect that the yellowing is due to either dryness or waterlogging. I know this sounds contradictory, but without seeing the plants or their pots, it could be either! Spring was very hot and dry and if you planted your agapanthus into large pots of compost it’s likely that, unless you watered well, the original rootballs dried out and were then difficult to re-wet. However, if they’re in very large pots, the compost could become too wet, which can cause rotting of the roots, especially for new plants.

AThis vigorous, variegated grass is beautiful in summer but can become invasive, especially in light soils. If you need to reduce it, dig it up and trace the underground stems. You can replant a few pieces elsewhere in the garden, or in a pot if you’re worried about its spread. Then, spray any stray shoots that spring up with a glyphosate-based weedkiller as they appear.