Flowering observations in Blackcurrants

We looked at one of our early blackcurrant bushes in full flower last week. The sun was shining, the bumblebees were working hard.  It was a beautiful sight.

We looked again a week after a -1.5°C frost (frost 17th Sept). The flowers were still all there, but instead of the shiny granny-smith green look of a healthy developing berry, the fruitlets had that slightly tan and shrunken doom-ladened look.  As we touched them, they fell off in bunches.  

Under the microscope we compared the inside of a healthy berry and a frosted berry.

The berry on the left looks good, while the one on the right most certainly does not.

Notice that on both berries, the stigma (there the pollen lands and sticks) is black.  It turns black after pollination, or after frost, so the stigma colour isn’t a useful indication of frost damage.

Make note of flowering dates by block:

One of the useful indicators for harvesting date is the flowering date.  Back in the late 90’s we did a lot of work on harvest date estimation and even developed models to determine optimum harvest date.  Unfortunately they required quite a bit of work prior to harvest and growers tend not to have sufficient time to do the analysis required.  One of the timings we almost used as a basis for the model was flowering date and we still believe that it is useful to have a record of flowering time on a block by block basis to use as a guide to work out the order of blocks for harvest.

The other check for harvest date is first black fruit.  Geoff uses that guideline as the key indicator for harvest date on the basis that 4 weeks after 1^st black fruit is about right for first harvest date.

Harvest date decisions are really important.  Sugar and anthocyanin levels increase over time.  The results from last season’s breeding plots highlight that increase over successive weeks so anything that helps determine the optimum harvest date is worth the effort.

We recommend:

• Check and record flowering dates block by block
• Double check with 1^st black fruit dates

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