Jasmine

Jasmine

Dave Clark sent me a photograph (no question attached) entitled simply “sooty jasmine”. The affected plant is the lovely scented evergreen Trachelospermum jasminoides, sometimes called star jasmine. The “soot” on it is similar to that which affects the lower leaves of many evergreens – most notably camellias – evident as they come out of winter inactivity and before they produce their new growth later in the spring.
The black mould – “soot” – is actually growing on the collected poo of minute sandy-coloured scale insects that live on the backs of the leaves, generally just visible around their central ribs. Washing the leaves, quite apart from being laborious and in most cases thoroughly impractical, does nothing to help. To control the insects you need to spray the entire plant (if practical) with a systemic insecticide such as Bug Clear or Provado Ultimate Bug Killer, aiming particularly to reach the backs of the leaves just above the worst soot. Eventually the new growth seems to outstrip the activity of the scale insects, and birds and other predators will nobble some of those on the young shoot tips, but this is likely to be a perennial problem.
Most trachelospermums I have seen recently have had a dreadful couple of winters, suffering from frost-nipped shoot tips and/or dramatic leaf drop.
As a general restorative treatment I would give them a feed and mulch, and – if they are growing at the base of brick walls in what is likely to be alkaline soil – an iron tonic of Sequestrene, since they do best in soil with a slightly low pH.

Jasmine