Hi there! I am wanting to use sugar as a foliar spray on my grapes. Can you advise me at what stage of growth is it best to apply and the ratio of sugar to water? Also how often can you spray before damage can occur and what sugar is the best brown or white? Kind Regards.
Follow this link for our Agronomy Notes on the proper use of carbohydrates: http://asktheplant.com/carbohydrates-sugars/
I would not recommend applying any form of carbohydrates without knowledge on the proper levels of Nitrate-Nitrogen in the sap. TPS Lab’s Ask the Plant® Sap (Petiole) Analysis of grapes beginning at pre-bloom thru veriason is essential to prevent any detrimental effect on the plant. Our agronomy notes on grapes can be found here: http://asktheplant.com/ask-the-plant-grape-specific-testing/
Applying carbohydrate converts the excess Nitrate used for vegetative growth to an amine form and forces the plant to convert that energy into natural carbohydrates thus increasing fruit set. Applying the sugar to low Nitrate-Nitrogen levels will actually stunt the plant which in effect cause less fruit set.
As far as the rate is concern, it will depend on the stage of growth as well as the levels of Nitrate-Nitrogen in the sap. The use of either brown or white sugar will lead to the same affect but may as lead to some insect pressure if they are present. The use of blackstrap Molasses would be a better substitute since it contains good levels of Sulfur and other plant essential trace elements that contribute to overall plant nutrition.
Noel Garcia, CCA
VP of Operations and Technical Director