The bacterial blight that affects walnuts grows in response to warmth and moisture. The critical time is from bud-burst to mid January. Spraying with a copper spray is advised at bud-burst. Later sprays can be determined by climate conditions.

The NZWIG Research Group has worked with Dr Tim Jenkins to develop a "Climate Model" to help orchardists work out the optimal time for blight sprays.

Download the Excel Spreadsheet and enter temperature, humidity and rainfall data for your orchard. Hourly data is available from NIWA and some other weather stations and can be gained by logging in from the internet.

Clive Marsh has used the spreadsheet for a period relating to his orchard. We offer this as an example here.

• Clive's worked example (pdf)

• Excel Spreadsheet to download and use

• NIWA weather data

• Summary and comments on 07-08 Season - (pdf)

To download files to your computer, right-click on the link and chose "Save link as" or "Save Target as"