Wine grapes are an important crop in Michigan. According to the National Association of American Wineries, the overall economic impact of Michigan’s grape and wine industry is estimated to be more than $6.3 billion annually. This includes the direct impact from vineyard and winery operations, as well as indirect effects such as wine tourism, related retail sales and hospitality services.

However, grapevines are highly susceptible to plant viruses. In fact, grapevines commonly host multiple plant viruses — sometimes multiple viruses infect a single vine. That’s why Michigan State University researchers are working to keep vineyards healthy and productive.

“The first step in controlling viruses is knowing which ones we have in Michigan — and now we know,” said Timothy Miles, associate professor and principal investigator for the Small Fruit and Hop Pathology program in MSU’s Department of Plant, Soil and Microbial Sciences in the College of Agriculture and Natural Resources.

Conducted by researchers from MSU and the University of California, Davis, the study aimed to determine what grapevine viruses are infecting Michigan’s vineyards to increase awareness of the importance of diagnostic testing and planting virus-free plant material.

Miles and his team used real-time reverse transcription polymerase chain reaction, or RT-PCR — the same detection technology often used in COVID-19 analysis — to test for a variety of grapevine viruses that are known to occur in other regions to see if these viruses have infiltrated Michigan’s grapevines.

Vineyards across the northwest, southwest, middle and southeast regions of the lower peninsula of Michigan were screened for a panel of viruses. Across all samples, grapevine rupestris stem pitting-associated virus, or GRSPaV, was the most abundant. 

Kerri Neugebauer, laboratory manager in the Small Fruit and Hop Pathology program said, “GRSPaV can cause poor spring growth, delayed bud break, stunting, reduced yield and results in a decline of the overall health of the vine.”

In the paper, the researchers discuss how Michigan faces challenges with grapevine viruses due to the following: 1) multiple Vitis species, which are wine grapes and juice grapes cultivated within the state and have varying levels of susceptibility to viruses; 2) vineyards vary in age; and 3) plant material is sourced from a variety of locations throughout the United States, which increases the risk of bringing virus-infected plant material into Michigan.

According to Miles, the biggest outcome to the study is that growers across the state now can test for these viruses through MSU’s Plant and Pest Diagnostics laboratory.

“Michigan’s unique Great Lakes climate allows us to grow high-quality wine grapes,” said Jenelle Jagmin, director of the Michigan Craft Beverage Council, which is part of the Michigan Department of Agriculture and Rural Development. “But this climate that differentiates our viticultural areas also presents specific challenges. Miles’ research helps tackle some of the unique pressures that Michigan grape growers face regarding disease and pest management. In addition to providing useful technical information, Miles is consistently found in the field with industry members. His work values science and application for the advancement of Michigan’s wine growing industry.”

Overall, the study provides valuable insights into the distribution and prevalence of grapevine viruses in Michigan, aiding growers in making informed management decisions to improve vineyard productivity and sustainability.

The paper was published in the peer-reviewed journal Plant Health Progress.