Kiwifruit leaf fall PSA control

During this transition period, Pseudomonas syringae pv. actinidiae (Psa) becomes the dominant disease threat, with leaf fall representing one of the most critical infection windows of the season. Leaf fall results in thousands of fresh leaf scars on each vine. These wounds act as direct entry points for Psa into cane tissue, allowing infections to establish and remain latent over winter before developing into cankers in spring. Copper, either applied alone or in combination with elicitors such as Actigard during leaf senescence, is used with a clear objective: to protect exposed leaf scars and restrict bacterial entry.

Psa susceptibility is lowest at the onset of leaf fall in late summer or early autumn and increases progressively as leaf drop continues and environmental conditions deteriorate. Cooler temperatures, higher rainfall, elevated humidity, and longer canopy wetness periods all favour bacterial survival and infection. Consequently, maintaining protection becomes increasingly important as leaf fall advances.

Preventative Psa programmes should begin as soon as practicable after harvest, with follow-up applications commencing once leaf fall starts. Application frequency and timing should be guided by the length of the leaf fall period and prevailing weather conditions. Where possible, copper applications should be timed ahead of forecast rainfall events or cold southerly weather patterns, as these conditions significantly elevate infection risk.

Recommended leaf fall programme

• Early leaf fall (20–30% senescence): Apply Nordox 75WG @ 55–70 g/100 L or ChampION @ 90 g/100 L, in combination with Actigard @ 200 g/ha.
• Mid leaf fall (50–60% senescence): As infection pressure increases sharply with ongoing leaf drop, reapply Nordox 75WG @ 55–70 g/100 L or ChampION @ 90 g/100 L.
• Late leaf fall (70–80% senescence): Infection risk is highest at this stage as winter conditions establish and the majority of leaf scars are exposed. Apply Nordox 75WG @ 70 g/100 L or ChampION @ 90 g/100 L.

Multiple applications are required throughout leaf fall because copper only protects existing leaf scars. Each newly shed leaf creates a fresh, unprotected wound, and leaf fall typically extends over several weeks. Repeated applications are therefore essential to maintain continuous protection. Once leaf fall is complete, one to two copper applications during winter dormancy are recommended ahead of extended cold and wet periods. Nordox 75WG offers strong persistence, making it particularly well suited to winter Psa management programmes.

Copper should never be applied below label rates for Psa control, and achieving excellent spray coverage is critical. While copper will not eliminate Psa entirely, well-timed leaf fall applications significantly reduce bacterial canker development and inoculum pressure heading into spring. Growers must also remain mindful of Zespri’s annual limit of 8 kg of active copper per hectare, requiring careful planning of total seasonal copper use.