We’ve been told for years about the importance of including Zinc (Zn) in our pre-bloom foliar nutritional sprays, so much so, that we almost universally include it without even thinking about it. I’d like to highlight the why behind pre-bloom Zn and also stress the critical role Calcium and Boron play (in conjunction with Zinc) in pre-bloom nutrition. Here’s a quick synopsis of what each element does for the plant and why it’s a necessary component in pre-bloom nutrition.
- Calcium (Ca): Is the key component in cell walls, maintaining membrane structure and has a direct influence on the regulation of enzyme systems, phyto-hormone activities, and nutritional uptake. It has a specific influence on fruit quality, color, and aroma. Low Ca concentrations in fruit lead to earlier maturity and softer skins in direct correlation to fruit quality in table, raisin, and wine grapes. Nearly 40% of a vine’s Ca absorption takes place between leaf emergence and fruit set.
- Boron (B): Is involved in various enzyme systems and carbohydrate metabolism. It also plays a critical role in pollen tube formation and fruit set. Low B concentrations can lead to shot berry, uneven ripening and, in the case of wine grapes, seedless berries. Due to its high solubility, foliar applications of B are very effective in correcting deficiencies. Typically, 90% of the applied B is taken up by the plant within 24 hours. Pre-bloom foliar applications are the best way to ensure pollination and fruit set problems are avoided.
- Zinc (Zn): Is a key component in the development and function of growth regulators (i.e. auxins) that influence internode elongation, rachis stretch, and bunch formation. Deficiencies can lead to poor fruit set, stunted shoots, and loose clusters with undersized, irregularly shaped fruit that ripens unevenly.
Before you think about making a nutrient application, it’s always important to get some history and a current tissue analysis to determine the rate and type of nutrient you need to recommend. Once you’ve determined need, the two final critical factors are when and with what.
The when is simple, the earlier the better. If you can get your pre-bloom on just as the infant cluster is emerging from the shoot, you will ensure the nutrients have time to absorb and translocate to the structures as they are forming. Including Megafol® and Exploit® in your spray will help kick-start the vines metabolism and help drive nutrients to the fruiting structures. I like to see a minimum of 2 pre-bloom (cluster emergence & 7 days pre-bloom) foliar nutrient applications in varieties that don’t have historical set issues and 3 applications (cluster emergence, 7 days pre-bloom, & bloom) to varieties that struggle with set, cluster development, and berry formation. These would be tank mixed with the grower’s powdery mildew applications.
A simple and easy pre-bloom program that is very effective is Brexil® CBZ + Exploit + Megafol. You get a great ratio of fully chelated Ca (5%), B (1%), Zn (3%) with the CBZ plus the metabolic benefits of Megafol and eXploit working together to maximize nutrient uptake. Should you have adequate B, another great option is tank mixing Brexil Zn (10%) + Brexil Ca (15%) + Exploit + Megafol. The Brexil Ca has a very small amount of B (0.5%) but not enough to influence tissue levels. Here’s the bottom line: we have a great number of tools available to help our growers maximize yield and quality. The key is timing, rates and superior inputs.
Paul W. Crout, CCA, PCA
AGRIntelligence|Agronomy|Organics Manager