Using Micro-Nutrients to Control Shattering of La Crescent Grapes (Cold-Climate)

View the project final report

Commodities

• Fruits: grapes

Practices

• Crop Production: fertilizers, foliar feeding, nutrient management

La Crescent is a cold climate grape variety developed by the University of Minnesota and well adapted to production in Wisconsin. La Crescent is very cold hardy and disease resistant and has many other positive characteristics. One issue with La Crescent is that the grape will shatter when near "peak ripeness". Shatter is when the berries fall off of the rachis. Shatter can be caused by a number of factors including high winds, disease pressure, and movement of the canopy during harvesting, especially during mechanical harvesting. Suggestions within the industry are that the nutrient, calcium, along with adequate levels of other micro- and macro-nutrients may be used in the prevention of shatter. To test this idea we performed field trials using several forms of delivery and products of the nutrient calcium. We used tissue analysis (petiole and hand-held sap analysis) to determine micro- and macro-nutrient levels within our plants through-out the trial. Yield projections and analysis helped us measure the degree to which shatter was or was not occurring.

Soil Test were conducted thru UW-Marshfield lab. Results showed adequate to high levels of N, P, K, Ca, S, Mn, B, Fe, and Cu. While it showed low levels of Mg, and Zn. Our average soil Ph is 6.9 which is acceptable for grapes. We therefore operated on the hypothesis that it likely wasn't an elemental deficiency in our soil causing shatter but rather also operating on the principle that high level of calcium, specifically at bloom and berry development can help prevent shatter.

To study the effectiveness of calcium management programs in helping prevent shatter we decided it would be best to use several different modes of applications and products. The modes and products we are testing for our calcium study are; soil applied gypsum, a single application of a foliar calcium fertilizer at bloom, two treatments of foliar applied calcium at bloom and then 2 weeks later, and Agro-K ‘s nutrient management program (which includes several calcium applications). We sampled 24 plants for each treatment including a control group of 24 which received no treatment. We sampled 4 rows, with each treatment type being 6 continuous plants. The order in the rows in which the treatment types were selected in each row was randomized. We also skipped a row between each sampled row to avoid drift of foliar sprays. All treatments were applied at industry recommended levels. Agro-K's testing, analysis, materials, and program were provided to us at no cost or incentive. 

We conducted our spray treatments at 1200 growing degree days (GDD), which is accepted to be the measure of halfway through the grapes physiological development (it's about half its final weight). By determining clusters per plant, the average weight of those clusters at 1200 GDD, and then multiplying by a factor of 2, we can estimate the final yield in terms of weight. I refer to this as our expected yield (EY). We can then quantify the effectiveness of these different treatments in reducing shatter by harvesting at peak yield, weighing and recording each treatment sample separately and measuring the difference between our actual yield and our EY. We chose to express this value as "% of EY" (harvested). Values of higher EY.

We also conducted petiole analysis in the lab and petiole analysis through hand-held technology. (results and analysis pending)

We also conducted pH, Brix, titratable acidity and yeast assimilable nitrogen. (completed, will insert results following another year of the project).

Yield analysis is presented as a table:

Our data shows that our control treat has the highest % of EY value making it in this instance according to this metric the most effective treatment. This is addressed in other sections of our analysis but short growing season contingencies, mainly vine decline from a recent polar vortex, may have affected our data set in a meaningful way. Because of this we believe it necessary to conduct this study for another year and gather more data and further analyze all data gather such as juice quality, and petiole results and how foliar sprays may or may nor effect them.

Yan tests were also done in 2020. The data below is shown as a table:

Due to COVID-19, there was limiting testing in 2020. Specifically, only the finished crop was tested. This data showed no significance between 2019 and 2020 in the shattering of the grapes during harvest. The different calcium treatments showed no effect on the chemical composition of the grapes, and visually, all of the plots looked the same. 

1. Determine if handheld nitrogen and calcium sap testers are accurate in getting immediate field levels as compared to lab petiole tests.
2. Evaluate if high levels of soil applied calcium and foliar applied calcium reduce shatter in La Crescent Grapes.
3. Measure grape juice quality on all treatments.
4. Share data following year one and year two with grape growing organizations in Wisconsin and Minnesota and on social media.