Quick Dips

Old Man's Beard May Go

The aggressive smothering problem weed Clematis vitalba -- better known as Old Man's Beard -- may be stopped in its tracks thanks to a new strain of fungus, Phoma clematidina.

A six-year search by HortResearch has resulted in discovery of a US variety of P. clematidina that can control the clematis; the original strain in New Zealand was not powerful enough. The testing programme involved extensive host range studies to check that the fungus does not pose a threat to any native clematis species.

The new variety has now been released at Taihape, Awapuni and Aokautere, and is performing well.

Landcare Research has also released Phytomyza vitalbae, a natural insect enemy of the clematis pest. It is hoped the two biocontrols will work together to "trim" Old Man's Beard.

Concerns have been raised about another pest, a sawfly, which strips willows. Established in Auckland, the sawfly could spread widely under New Zealand conditions; in Argentina and Chile a similar species spread 3,000 km in ten years.

The sawfly larvae are capable of defoliating willows at least twice each summer, causing major damage to root systems and toppling trees.

Our willows are particularly vulnerable because there is a very small genetic base of river crack and golden willow plantings. The trees play a valuable role in river control and soil conservation.

From 1998, HortResearch will study the possible introduction of biological controls, including parasitic wasps.

They also intend to take a long-term willow introduction and breeding approach focused on improving the genetic diversity of willows.