Farmer Guides

Pests and Diseases

The Willow sawfly is found throughout New Zealand
Their larvae feed exclusively on willows with all varieties being susceptible
Emerging larvae eat a ‘window’ in the leaf, and then feeds along the edge of the hole. After moulting it usually moves to the edge of the leaf, and continues to feed.
Damage from willow sawfly is serious but periodic and the future risk is considered low

This very large aphid appears as colonies in summer
By late summer there may be tens of thousands on a single tree
It has an adverse impact on tree growth, exacerbates the effects of droughts and the honeydew they produce attracts wasps
Control with systemic pesticides is possible
Biological control agents are being sought

A single poplar sawfly, Cladius grandis (Tenthredinidae), larva was detected in a gypsy moth trap in Dunedin in February 2019
Adults: 6-9mm; overall reddish yellow, head and part of thorax black; wings yellowish hyaline strongly iridescent, venation reddish yellow
Larvae: up to 16mm; overall yellow with two lateral rows of black spots (dorsal much larger than ventral) and whitish hairs; head blackish and brownish except some yellow spots on the frontal part
Host plants include species from Family Salicaceae: Populus alba, P. balsamifera, P. canadensis, P. dilatata, P. monilifera, P. nigra, P. tremula, P. pyramidalis, Salix caprea (pussy willow).