On the Grow: Seedless Table Grapes Coming To New England?

After seven years of study, University of New Hampshire (UNH) researchers with the New Hampshire Agricultural Experiment Station (NHAES) report that seedless table grapes soon may be a viable option for local growers despite the state’s climate.

Their findings, published in HortScience, show that choosing the right variety and using strategic vineyard management are crucial for growing table grapes in northern climates, but the production performance of grape varieties such as ‘Mars’, ‘Canadice’, and ‘Lakemont’ offer potential for a commercial seedless table grape industry in New Hampshire and New England.

“There are several seedless table grape varieties that are well adapted to our region,” NHAES scientist Becky Sideman says. “These varieties bring delicious and unique flavors to consumers, and they expand the options for local producers.”

While grape production in New Hampshire is slowly expanding, there were only 106 acres of grapevines in 2022. Several studies have looked at growing cool-climate winegrapes, but seedless table grapes had yet to be systematically evaluated.

UNH researchers worked to begin closing that knowledge gap, led by Sideman, Research Scientist Kaitlyn Orde, and George Hamilton, UNH Extension Fruit and Vegetable Field Specialist Emeritus.

The research focused on eight table grape varieties that had previously performed well in a southern New Hampshire trial vineyard while using two vine training systems — vertical shoot positioning (VSP) and Munson — to evaluate their potential for commercial growers.

GRAPEVINE VIGOR

The eight seedless table grape varieties studied were ‘Canadice’, ‘Concord Seedless’, ‘Lakemont’, ‘Marquis’, ‘Mars’, ‘Reliance’, ‘Thomcord’, and ‘Vanessa’. After the vines were planted, they were not permitted to set fruit until their third year of growth. Vine vigor was evaluated in the first and third year. The researchers found the vines of two of the varieties, ‘Thomcord’ and ‘Marquis’, to be less vigorous than the others. Both were also the most susceptible to fungal grapevine diseases, exacerbated by the damp New Hampshire climate. By the end of the fourth year most of their vines were very weak or dead, so they were removed from the experiment.

The research team measured susceptibility to pests and disease, fruit yield and quality, and weight retention after harvest — an indication of how well the fruit would handle storage — of the other six varieties for five years. They tracked the varieties’ overall performance as well as year-to-year variation due to different weather conditions. They also assessed the differences, if any, between the VSP and Munson vine training systems.

VIABLE COMMERCIAL CROPS

In sharp contrast to ‘Thomcord’ and ‘Marquis’, the ‘Concord Seedless’, ‘Canadice’, and ‘Mars’ vines showed notable resistance to fungal disease. Importantly, the researchers also did not observe problematic levels of common diseases that attack the grapes themselves, including black rot and botrytis bunch rot. After the harvest, ‘Mars’, ‘Reliance’, and ‘Canadice’ had limited weight loss in four weeks of cold storage, indicating that they may be held and sold for longer periods of time than other varieties.

Interestingly, the research team initially found higher yields with the VSP vine training system, but they were overtaken by the Munson system vines by the end of the study. While it takes longer to establish, the Munson system may help growers maximize their yields and quality over the long term.

Overall, ‘Mars’, a blue grape with a slipskin — a variety in which the skin separates from the berry flesh — is perhaps the most promising variety for aspiring New Hampshire seedless table grape growers. It was disease and pest resistant and had high yields and excellent fruit quality. While its yields were lower, Canadice, a red slipskin grape, also had high marks in the other performance categories. ‘Lakemont’, a green grape, and ‘Vanessa’ (red) did not yield quite as well, but they are non-slipskin grapes and their fruit quality matched that of ‘Mars’ and ‘Canadice’, providing additional potential options for growers.

“We hope that this research helps prospective table grape growers in colder climates understand the strengths and limitations of different varieties, and that this will ultimately lead to more local table grape production in northern New England,” Sideman says.