By: Brooke Dietsch
Brooke is a Graduate student of Dr. Suzanne Slack, an affiliate professor with the Department of Horticulture at Iowa State University.
SHW and GDC La Crescent and Marquette Grapes covered in bird netting.
The ISU Horticulture Research Station is gearing up for the grape harvest, a crucial phase for both enological and viticultural research, as well as wine production facilitated by the Midwest Grape and Wine Industry Institute. Established in 2011, our vineyard comprises La Crescent and Marquette cultivars, trained using the Single High Wire (SHW) and Geneva Double Curtain (GDC) trellis systems. Presently, we’re engaged in two research initiatives: one centered around plant growth regulators, and the other exploring diverse canopy management techniques. The convergence of these research pursuits and the presence of the two trellising systems necessitate early-season harvest preparations. This ensures accurate data collection, facilitates manual harvesting, and yields top-notch berries for the Midwest Grape and Wine Industry Institute.
Preparations for harvest have been underway since veraison initiated in early July, advancing steadily throughout the season. Upon observing the color shift in the berries, our students initiated rigorous weed management within the plant rows. This action aimed to mitigate seed set and flowering, anticipating reduced levels by harvest. Simultaneously, it aimed to curtail weed growth under the bird netting, which was subsequently installed. Preemptively fitting both cultivars and trellises with bird netting, prior to full color change, and installing a short electric fence as a raccoon deterrent has notably curbed bird and insect damage to the berries.
Starting from early August, we’ve been regularly extracting berry samples for analysis by the Midwest Grape and Wine Industry Institute. Parameters such as pH, Brix, and tartaric acid levels have been monitored weekly throughout the month, aiding the decision-making process for harvest timing. The determination of harvest timing leans primarily on the desired pH levels for the specific wine types to be produced. This choice stems from the understanding that while Brix holds importance, sugar levels can be adjusted during the winemaking process. Additionally, our cold-hardy cultivars exhibit naturally lower pH values, making pH-based harvesting a preferable approach to potentially enhance wine quality.
Currently, our GDC vines are approaching optimal levels slightly ahead of the SHW vines. Our estimate points to both being ready for harvest around the weeks of August 28th or September 4th. Once the indicators align favorably, the harvest will be conducted manually. Initially, research panels will be assembled, and vital metrics such as bunch weight, size, and shoot length will be recorded in the field. Subsequently, these bunches will be segregated for further in-depth analysis of the berries and other plant components. Afterward, the remainder of the vineyard will be harvested, with the yield destined for the Institute to facilitate wine production and future distribution.