Host of the month - Plane

‘Host of the month’ is a series of Blogs and PDF’s that highlight a tree host and their associated priority pests and diseases that are best seen and recorded in that month. For September we’re looking at Plane trees, Plane lace bugs and Plane wilt.

Planes are the only Genus in the plane family, the Platanaceae with 11 species currently recognised. Planes are not native to the UK, but Oriental plane (Platanus orientalis) is found across south-east Europe, Asia and India. London plane (Platanus x hispanica) is a hybrid between Oriental and American plane (P. occidentalis) that was first planted in England around 1680 at Ely in Cambridgeshire, and at Barnes in Surrey and both trees are still there today, the latter one going by the name of Barnie.

Planes are adept at trapping particulates such as airborne pollutants on both bark and leaf hairs and can survive in very poor compacted ground which makes them well suited to life in cities and towns where they provide cooling shade. Unfortunately, they are seriously affected by the plane lace bug and plane wilt, neither of which is currently known to be present in the UK, but both are causing damage to Plane trees in mainland Europe.

Plane lace bugs

Plane lace bug is native to North America and was accidentally introduced to mainland Europe. A small population was found at a plant nursery in Bedfordshire in 2006 but was successfully eradicated and the pest is not yet known to be present in the UK. Very heavy infestations will lead to premature leaf drop and can, after several years, kill younger trees.

Identification

Adult Plane lace bugs are around 4mm long with lace-like wing covers with some brown colouring at their base and are usually found on the underside of infested leaves, often accompanied by the nymphs which are shiny black and oval shaped with a scattering of black spines. The first sign of lace bug presence is the appearance of small pale green or yellowish spots on the upper surface of leaves, usually clustered along the leaf veins. With increasing numbers of lace bugs the spots gradually coalesce resulting in whole leaves taking on a chlorotic pale-yellow colour with areas of bronzing.

Plane wilt

Also known as Canker Stain of Plane, is a fungal disease of Oriental, American, and London planes. It affects the water transport systems of the tree causing wilting of leaves and shoots and is usually fatal within 5-7 years. The fungus is native to North America and was first found in Europe in Marseille, France, in 1972. It is now present in France, Italy, Switzerland, and Greece.

Identification

The most visible symptom of infection is the sudden wilting of leaves, often initially on a single branch but soon spreading. As the infection progresses and spreads to the crown of an infected tree it becomes sparse and thin with discoloured leaves.

Several other common pests and pathogens can affect plane trees, some of which produce symptoms like those caused by plane lace bugs or plane wilt. They include plane anthracnose, plane powdery mildew and leaf hoppers.

For more information on the symptoms of Plane lace bugs or Plane wilt and lookalikes see their Observatree resources pages or the relevant Host of the Month.