Using microelements to improve fruit set in blackcurrants

Geoff Langford

There are some basic principles we should remember:

1. Foliar fertilisers do not substitute for the basics of good soil quality and healthy roots

2. Roots are the way plants take up nutrients and the amount of nutrient that other plant parts can absorb is very limited

3. As has been shown with bitter pit management in apples, hard to transport elements like calcium (and boron) can be applied by foliar treatment and make a difference

4. Frequency of application is important when applying foliar treatments

Some interesting facts associated with the trial last season:

1. Only 2 sprays were applied in the critical time period associated with flowering (grape and early flowering (a week apart)
2. No calcium was applied during the pre-fruit set period
3. The Yara treatment applied 2 amounts of 174g/ha of Boron (175g of sugar is three quarters of a cup.  Visualise that spread over 1 ha!)
4. The Valagro treatment applied 31g/ha and 56g/ha of Boron in those two sprays
5. Both treatments gave a small yield improvement

The full project report was sent out by email 28.4.26, and can be accessed by contacting BCNZ.

This raises questions about how to get better value from foliar treatments.  My thinking is that if it was practically feasible, twice a week from grape to full flower (about a 3 week period) would be a target.  This could be up to 6 applications and drone spraying might be a useful application option for this sort of frequency.

1. Include calcium with the boron treatments
2. Increase the frequency of application to at least two applications per week over the grape stage to full flowering period

Don’t lose sight of the basics

Another highlight from the project was the wide variation of % fruit set between blocks, independent of the foliar treatments.  We believe soil health is a major factor in play here.  Let’s go the lighthearted route and see how active the soils are by using the “Soil your Undies” exercise, where cotton cloth is buried and soil activity rate (decomposition) is measured by how much fabric is left after 3 months.  Be prepared to guffaw, but learn something nevertheless.