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last updated Feb 3, 2011
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Bay sucker. RHS/Science.

Bay sucker can spoil the appearance of a bay tree by causing discoloration and distortion of leaves at the shoot tips.

What is bay sucker? Back to top

Bay sucker is a small sap-sucking insect that attacks the foliage during the summer. It is the immature nymphs that cause most of the damage.

Symptoms Back to top

  • Bay tree leaves thicken, curl downwards at the margins and turn yellow; often only one half of the leaf is affected
  • The discoloured areas later dry up and become brown 
  • Small greyish white insects may be seen underneath or near the curled leaf margins

Control Back to top

Non-chemical control

  • For light infestations pick off and dispose of infested leaves
  • Badly affected shoots can be pruned out in winter. This will encourage new growth in the spring and may remove some overwintering adults

Chemical control

  • If an insecticide is necessary and the plant is small enough to be sprayed, it can be treated with the ready-diluted formulation of the systemic insecticide thiacloprid (Provado Ultimate Bug Killer Ready To Use)
  • If the leaves are being used for culinary purposes, a minimum 14-day interval must be left between spraying and using the leaves
  • Only one application a year is permitted with this insecticide on herb plants, so it is important to apply it when signs of new damage are first seen in May

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

Biology Back to top

The damage is caused by the nymphal stages of the bay sucker when they suck sap from the young leaves during the summer.
  • The winged adults are greenish brown and about 2mm long (less than 1/8in), and they overwinter in sheltered places
  • In April to May, the adult suckers emerge and start to feed, causing the leaf margins to begin curling under. Eggs are laid under the curling leaf margins
  • The young nymphs are grey, flattened wingless insects, whose bodies are covered with a white fluffy material
  • Like the adults, the nymphs also suck sap and increase the leaf curling and discoloration
  • Two or three overlapping generations occur between May and September

Quick facts

Common name Bay sucker
Scientific name Trioza alacris
Plants affected Bay (Laurus nobilis)
Main symptoms Leaves develop curled leaf margins that are abnormally thickened and pale yellow. Greyish white insects may be seen under the curled leaf margin. Later the damaged parts of the leaf dry up and turn brown
Most active May to October

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