Immature currants on a branch. Credit: Stock image / Pixabay

Although neighboring states allow it, growing currants, gooseberries and other related berries is prohibited in Maine. And though some gardeners wish the law would change, there’s a good reason for it, experts say.

Plants like gooseberries, currants and European black currant belong to the genus Ribes, which includes more than 200 species. And though they have caught on in health food circles and pick-your-own farms elsewhere, plants in the genus Ribes are the required host for a devastating fungus called white pine blister rust, which infects and eventually kills the Eastern white pine trees that fill the forests of Maine.

Recently, gooseberries, currants and European black currants have gained popularity among U-pick small fruit growers and health food stores.

“People are always looking for the next superfruit and currants are very high in antioxidants,” said David Handley, vegetable and small fruit specialist at the University of Maine Cooperative Extension.

Despite the health benefits, Maine remains steadfast in its laws against Ribes for the sake of the state’s forests.

Allison Kanoti, state entomologist at the Maine Forest Service, said the fungal spore hosted by a Ribes species will land on the needle and the fungus will grow into the branches and eventually infect the main stem of the tree.

“When it gets into the main stem, it can cut off the flow of water and nutrients in that tree and cause the tree to die,” Kanoti said. “It can also cause decline and reduce productivity of those trees as well.”

Ripening gooseberries on a branch Credit: Stock image / Pixabay

Tom Doak, executive director of Maine Woodland Owners, a statewide organization supporting Maine’s 86,000 family woodland owners, said that white pine trees that are infected with this fungus will exhibit “weeping” sap in the nodes of branches.

“The biggest threat to the forest in Maine isn’t fire or wind or rain or hurricanes, it’s really introduced pests from other places that have no natural control,” Doak said. “That’s what was going on with blister rust.”

Luckily, scientists have known about this connection between Ribes and white pine blister rust for over a century. The federal government banned growing all Ribes in 1911, even employing eradication groups to remove the plants. The U.S. lifted the ban in 1966, but Maine implemented its own statewide ban in 1979 to protect its white pine tree populations.

The exact stipulations of the ban depend on location and the species, determined by the concentration of white pine trees in a given area. Outside the areas with the highest concentration of white pine trees in Maine it is legal to grow currants, gooseberries and some other Ribes varieties. However, growing the European black currant, Ribes nigrum, is prohibited throughout the state because it is an especially virulent carrier for white pine blister rust.

Every so often, renewed interest in the currants, gooseberries and other Ribes causes some resistance to the rule from growers and gardeners. Handley said there have been several efforts to overturn these prohibitions in Maine, including once in the early 1990s and again around 2011. At that point, there were a couple Ribes varieties, particularly black currants, that seemed to show resistance to white pine blister rust.

The Portland Press Herald reported about a group of gardeners who were trying to make it legal to grow currants in Maine again. They even had the support of the then-executive director of the Maine Organic Farmers and Gardeners Association (MOFGA), Russel Libby, who said the ban isn’t effective.

Not so, say state experts. Though the white pine blister rust-resistant varieties of Ribes seemed promising at first, over the past 20 years since they have been planted that immunity broke down as the plants crossbred with native varieties.

“That resistance or immunity had failed,” Kanoti said.

Reduction of these species has been proven effective in controlling the fungus. Kanoti said that the state’s retired pathologist, William Ostrofsky, authored a study in 1988 that showed significant reductions in white pine blister rust in areas where Ribes were controlled. She added that white pine trees continue to have an increasing presence in the state, with stocks increasing even in the last 10 years, and that can be credited in part to the Ribes ban.

“I think white pine blister rust is one of the success stories with a relatively simple solution that doesn’t cost a huge amount of money,” Doak said. “[You’re] not spraying [chemicals], just don’t plant these things and pull them when you find them. It is a relatively inexpensive way to deal with what is an incredibly valuable resource both economically and as a component of the forest.”

Handley said unless the timber industry were to reach out to find some compromise with small fruit growers — which, given the risk, they are unlikely to do — the ban will likely stay in place for the foreseeable future. And that’s probably for the best.

The economic potential for growing Ribes in Maine is a drop in the bucket compared to the value of white pine trees which, according to a 2019 report, is conservatively estimated to exceed $2 billion.

“They’re a fascinating crop and they’re a good crop, but I realize the potential danger that this poses for the forest industry,” Handley said. “Maybe there’s a compromise in there where small growers or even home gardeners would be able to do this, but it puts a big burden on the Department of Agriculture because now we have to have someone running around making sure people play by the rules.”

Ribes need to be processed, whether by adding sugar to make them palatable for a juice or to process the berries into a tincture, which are skills and infrastructure that the state does not possess at scale.

“That is going to require some investment and some skill that you may not have the ability to handle at this time,” Handley said.

For growers interested in growing berries with antioxidant benefits, Handley said there are plenty of alternatives that don’t carry white pine blister rust. They include blackberries, chokeberries, elderberries and even Maine’s iconic wild blueberries.

Speaking of icons, what would Maine be without the Eastern white pine tree?

“Look at our state emblems,” Kanoti said. “We are the Pine Tree State, right? Our state tree is the Eastern white pine. It’s really hard to exaggerate the importance of white pine in Maine.”

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