Psa risk rises for some regions next week

19 March 2020

The Psa Risk Model currently predicts moderate Psa infection risk for next week in some regions including Kerikeri, Whangarei, Waikato, Katikati, the Eastern Bay of Plenty and Wanganui.

Parts of Nelson are also showing a three-day period of moderate risk early in the week.

This reflects increased Psa risk with the cooler autumn weather and increased likelihood of rain, and is a reminder to growers to keep watching the model and to consider their Psa management plans, particularly for recently harvested blocks and younger plantings.

Cold stress can lead to expression of symptoms and growers with young plantings or less tolerant varieties are recommended to complete a monitoring round if they are in higher risk locations – early this week a Kerikeri grower confirmed exudate and leaf spotting found through monitoring of their previously Psa Not Detected site. This follows a period of colder weather two weeks prior.

High winds and frost can also provide entry points for Psa. Growers with developing blocks exposed to the elements should consider dropping laterals and ensure good protective spray coverage is in place before rain.

For early harvest blocks apply copper to protect fruit stalks. Apply copper alone if there is any risk of drift and then plan to follow up with an Actigard spray when neighbouring blocks have been harvested. A reminder though to be cautious in applying Actigard to vines that have been severely stressed by drought – it is not recommended for vines showing signs of stress such as wilting, premature leaf yellowing or leaf drop.

Risk model image below from the Karapiro weather station, Waikato.