Autumn Psa risk increases

26 May 2022

Autumn is typically a higher risk period for Psa as temperatures drop, rainy misty periods increase, and heavier dews also provide an opportunity for Psa multiplication and spread.

Monthly Psa risk plots available via the KVH Weather & Disease Portal, show this increased autumnal risk trend, and provide information on risk versus previous seasons.

The Mangatapere station in Northland for example shows that Psa risk increased through March and April and that risk is slightly higher this season (blue plot) vs the previous two years.

Growers can also use Psa risk model forecasts, to plan post-harvest and leaf-fall copper sprays and pruning activities. High or medium risk weather is currently forecast for much of next week in most regions, so growers are urged to get protective sprays on as soon as possible.

Development blocks exposed to frosts or wind need special attention as younger growth remains vulnerable to injury, providing opportunity for Psa entry. Good autumn protection is an important part of year-round management of this disease. Forecast risk of ground frosts can be accessed through the KVH Weather & Disease Portal here.