The Giant Willow Aphid was discovered in New Zealand in 2013. When it was then looked for it was found to be widespread and has probably been in New Zealand for 20 years.
It forms large dense groups on willows and poplars and sucks the sap from young stems and branches.
Identify the problem
The Giant Willow Aphid is one of the largest aphid species (up to 6 mm). It is brown with a pattern of spots including three prominent ones on the back of its abdomen. When squashed the aphids ooze a red blood-like liquid.
In high numbers during summer months the honeydew the aphids produce can fall like fine rain from affected trees. Wasps are often attracted to the sweet honeydew and where the honeydew coats leaves and stems sooty mould will start to grow.
Trees up to 4 m:
- Apply PLANThealth Insect Hit Granules or LawnPro Lawnguard to the soil around the roots of the tree out as far as the drip-line (reach of foliage).
- Spray reachable foliage with PLANThealth Spectrum.
Trees over 4 m:
- It is unclear whether using PLANThealth Insect Hit Granules or LawnPro Lawnguard as above will always work on all larger trees.*
*It has been found to be effective on some trees up to 20 m.
Note: The above retail products in black have been discontinued. However, if you have a significant problem a commercial option is still available, please contact Kiwicare directly for more information.
Did You Know
- The extent of harm caused by Giant Willow Aphids to the host plants is not well known, however overseas studies reported that giant willow aphid caused significant growth reductions during and after infestation. In New Zealand the extent of the damage remains to be seen, but this pest could pose problems where willows are used for flood protection and in shelter-belts. It has recently been found that giant willow aphids will infest apple trees as well as willows and poplars.
- The giant willow aphid is Tuberolachnus salignus
- Adults give birth to miniature aphids called nymphs. Each adult alate (winged adult) is reported to produce 30-40 nymphs. Nymphs develop in 12-17 days. Both winged and non-winged adult forms continue to survive after producing young. Reproduction is parthenogenic (asexual reproduction); no males are known for this species.
- It is thought by many that the increase in giant willow aphid numbers around many parts of New Zealand has caused an increase in wasp numbers because they produce large amounts of honeydew that the wasps will feed on.
- Where possible spray the undersides of leaves.
- Carry out a winter spray program on trees and shrubs in dormancy to kill aphid eggs hidden in bark and buds.