Thinking of thinning? Quick fruit size update

Friday, June 9, 2023

The cold temperatures this past week have put into question how quickly fruitlets would grow each day. Our usual assumption is that the fruitlets grow 1 mm each day at average temperatures. However, we have experienced cold daytime and nighttime temperatures and accordingly, fruit growth has been slow.

I measured twenty king fruitlets of each of the following varieties to get a rough average at the monitoring site on Middle Dyke Rd on Monday, June 5 and then again today on Friday, June 9. Today the Idared buds measured 9.5 mm, Honeycrisp measured 8.1 mm, and Ambrosia measured 5.9 mm. This means that the fruit growth rate was roughly 0.4 mm per day this week for the early varieties and even less for Ambrosia that had just reached the petal fall stage.

According to the current forecast, the sunny and warm weather (24°C) on Monday June 12 looks ideal for a good thinning response (and not excessive). The possible rain in the forecast may necessitate starting practices on Sunday, depending on the farm and if the rain remains in the forecast. In the coming heat, fruitlets are expected to return to a growth rate of roughly 1 mm each day.

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