Willow leaf beetles

The feeding activities of bronzy green or bluish black beetles and their black larvae can cause foliage of willows, aspen and poplars to dry up and turn brown.

Willow leaf beetle larvae ( Gonioctena viminalis )

Willow leaf beetle larvae (Gonioctena viminalis)

Quick facts

Common name Willow leaf beetles
Scientific name Several species in the genera Phratora and Crepidodera
Plants affected Willows (Salix spp), aspen and poplars (Populus spp)
Main symptoms Damaged leaves dry up and turn brown
Most active Summer

What are willow leaf beetles?

Willows and poplars can be attacked during the summer months by several species of leaf beetle. They are generally in the size range of 2-4mm long and are often bronzy green or bluish black in colour. These leaf beetles include four similar looking species of Phratora and five species of Crepidodera. The larvae of most species are soft-bodied, black larvae that often feed together in clusters.

Symptoms

The adults and the larvae of willow leaf beetles graze away part of the leaf surface, causing the remaining damaged areas to turn brown and dry up. In some years these beetles can be very abundant and by the end of the summer most of the foliage on large trees can be affected.

Fortunately, although the damage they cause can be unsightly, it is something that trees usually survive and severe damage does not usually occur every year.

Control

In gardens willow leaf beetle damage can usually be tolerated, even when most of the foliage on a tree is affected, as the trees usually recover and severe infestations do not usually occur year after year. On large trees there is no suitable treatment.

Non-pesticide control

  • See above - control is not usually necessary

Pesticide control

  • Pesticide control of willow leaf beetles in not usually necessary
  • Pesticide control of heavy infestations of willow leaf beetles can only be considered on trees small enough to be sprayed thoroughly
  • Pesticides are likely to be more effective on larvae than adults
  • Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer). Several applications of these short persistence products may be necessary to give good control
  • More persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
  • Follow label instructions when using pesticides
  • Plants in flower should not be sprayed due to the danger to pollinating insects
  • Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

Most willow leaf beetles have similar life cycles and are thought to have one generation a year. Adults can be found throughout the year and it is this stage that overwinters in crevices in bark, in dead wood and other sheltered places.

In the spring they emerge and mate and can probably lay eggs throughout spring and much of summer. The larval stage can be present from late spring and summer and feeds for a few weeks before dropping to the soil to pupate. New generation adults emerge before autumn and feed before overwintering.


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