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Alder sucker is a common on alder but the damage caused is seldom serious.
Alder sucker nymphs
There are several species of sucker or psyllid that can be encountered by gardeners, they are sap sucking true bugs. Alder sucker is only found on alder. The adults are similar in appearance to aphids and up to 5mm long, green with clear wings. The nymphs are also green with some black markings and flattened in appearance however, they are usually covered in a white waxy secretion.
The nymphs of alder sucker are covered by a ball of fluffy white waxy threads which can make it presence noticeable during the spring. They suck sap from the foliage during April-early June and these feeding activities may reduce the vigour of new shoots.
The adults, which lack the waxy secretions, are present from June-October. Overwintering eggs are laid on the shoots of alders (Alnus species) in the autumn.
Apart from the presence of noticeable white waxy deposits in the spring this insect rarely causes any damage to alders and there is no need to control it. Indeed alders being large trees would be hard to difficult in any case.
Alder leaf beetle
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