Despite the large colonies of large willow bark aphid that can develop they seem to have no significant effect on the tree's health or vigour and the presence of this insect can be tolerated.
Aphids have many natural enemies, including ladybirds, hoverfly larvae, lacewing larvae and parasitic wasps. Pest control products based on natural compounds or with a physical mode of action are less likely to have serious effect on natural predators.
If they are a nuisance because of the honeydew production, the aphids can be controlled on small trees by spraying insecticides.
- During the growing season there are many insecticides that can be used. It is only feasible to control aphids on trees that are small enough to be sprayed thoroughly. Aphid infestations on tall trees have to be tolerated
- Always read the label and use pesticides safely
- Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Organic Pest & Disease Control, Bug Clear for Fruit and Veg) can give good control of aphids. These pesticides have a very short persistence and so may require reapplication to keep aphid numbers in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults
- More persistent 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
- Plants in flower should not be sprayed due 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
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)