From monitoring early this week mature apothecia cups have been observed in the Annapolis Valley, but most blueberry varieties are still in the majority bud scale separation stage with a few buds entering the F2 stage. However, with the warm weather development may advance rapidly, and we will likely have our first infection period later this week, if we get the forecasted rain.
Monilinia requires blueberry plants to be wet from rain or fog to cause infection. The risk of infection increases with the longer the plant is wet and with warmer. Monilinia infection period severity ratings for specific wetness durations and temperatures can be found below (Table 1 ).
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| Table 1. Severity rating of Monilinia Blight infections based on the length |
Most growers will choose to apply with one of the Group 3 fungicides for their first application. Group 3 fungicides move rapidly into the plant after application and most have a rain fastness of one hour. They are also very locally systemic though, and windy conditions during application can effect coverage and decrease effectiveness.
If you are unable to get an application on before the rain, Group 3s have decent post infection activity and maybe applied up to 72 hours after an infection period and still provide some protection. However, there maybe some risk to relying on post infection activity, so growers should plan on applying ahead of wet infection periods.
