the Northeast took separate approaches to the issue. Some maintained scaled-down eradication programs. Vermont’s secretary
of state determined in 1998 that any bans on growing Ribes had
lapsed, though just when is something of a mystery. New York
designated berry-growing zones where Ribes could be planted.
New Hampshire relaxed its ban beginning in 1999, allowing the
planting of resistant gooseberry and currant cultivars with a
permit. As of 2012, there were 144 towns in Massachusetts that
still prohibit Ribes plantings.
Despite perennial pressure from would-be berry growers,
however, Maine never let its guard down. The eradication program was abandoned in the 1980s, though the state continues to
educate private landowners on Ribes eradication techniques if
they ask. Maine forestry officials successfully fended off repeated attempts to alter Maine’s statewide ban on the plants.
“In the southern part of the state, we have a viable white
pine sawmill industry and people were very protective of that
resource. And it’s going to take a long time to replace it if we lose
it,” said Struble, Maine’s state entomologist.
Struble said one reason that forest pathologists in the state
remained concerned was because all the resistant cultivars
had the European black currant, Ribes nigrum, as an ancestor.
That species, when infected with the rust, produces prodigious
numbers of spores. Maine forestry officials worried about what
could happen if a resistant variety hybridized with native Ribes
and passed that trait along to its offspring.
Not So Rust Resistant
In the end, the concern seemed prescient, though the new threat
didn’t come from precisely that direction.
In 2011, Connecticut researchers announced that white pine
blister rust had been confirmed in a large planting of Titania
currant, a variety supposedly resistant to the disease.
Earlier this year, researchers announced that DNA testing
had confirmed the presence of rust on 17 of 19 Ribes cultivars
sampled in New Hampshire, including four varieties of black
currant that had the Cr gene that supposedly conferred resistance. Spores collected from New Hampshire Ribes plants and
pines were then used to infect resistant Ribes cultivars stored
in the Canadian Clonal Genebank, proving the existence of a
mutated race of the rust. The researchers also said that sampling
showed that the chances of finding rust-infected white pines
near rust-infected Ribes plants in New Hampshire was much
greater than near non-infected Ribes plants.
“Results from this study suggest that the breakdown of
Cr-based resistance in Ribes poses a threat to the white pine
resource and to cultivated Ribes production,” the researchers
said in a draft version of a study slated for publication in the
journal Plant Disease.
Isabel Munck, a plant pathologist with the U.S. Forest
Service’s State and Private Forestry Program and the lead author
on the study, said the confirmation of a mutated pathogen is
“definitely cause for concern.”
“It’s a huge deal if it’s ignored,” she added. “Most of the white
pine resource is older. Because of that, it’s likely to be harvested.
What’s going to replace it is younger trees, and those are going
to be more susceptible to the rust. We need to encourage disease
management. I think it can be managed, but the key is not to be
Research has shown that pines under nine feet tall are most
vulnerable. That’s because the spores are more likely to land on
them and find favorable cool, moist conditions to keep them via-
ble until they enter the stomates. A young pine’s shorter branches
also mean a shorter journey from needles to trunk, where the dis-
ease can girdle and kill it. Still, trees of all ages can be infected.
It’s too early to say whether the new strain of rust is more
virulent than the original or just able to infect “rust-resistant”
Ribes varieties, said Munck. And given the fact that the mutated
strain was just discovered, it’s likely too early for plant breeders to
begin work on developing a new line of currants resistant to it.
Protecting the White Pine
The new rust pathogen poses a threat not just to the white
pine industry of the Northeast, but also to the small, until now
growing, gooseberry and currant business.
“I think it probably spells the end of it, unless they can come
up with new varieties that are resistant, which I’m sure they’re
working on. But then there’s probably going to be another one.
New disease strains come on, new pests come on,” said Peter
Hingston of Cherry Hill Farm, Vermont’s largest producer of
currants and gooseberries, with 18,000 bushes, mostly black
currants. The fruit is sold pick-your-own and to wineries and
ice cream and frozen yogurt makers.
Hingston wasn’t surprised at the news of the mutated rust
pathogen. “I thought I had seen it before,” about seven years ago,
on the supposedly resistant currant cultivar Titania he grows.
But no tests were done and an expert at Cornell assured him
Titania was resistant.
Then, last year, something attacked his currants. “Titania is
not a great variety, but it’s always performed reasonably well.
But last year it pretty much totally failed on us. The leaves fell
off and it just looked awful. We put the machine through and
picked everything we could. But it was pretty pathetic. The
fruit looked good, but there was very little of it. You can’t judge
something by one summer, and maybe it’s something else, but I
feel that that’s what that was,” said Hingston.
He sounds resigned, and often uses the past tense when he
talks about his currant and gooseberry crop. “I’ve enjoyed it. I
really enjoyed growing them. They’re a nice crop to grow. But
that’s not a very good reason for me to be growing them if there’s
definite proof that I’m going to do harm to the pine industry.
There’s plenty of alternatives in the fruit world for people to eat.”
Currant growers could probably combat the rust with a regi-
men of chemical sprays. But Hingston doesn’t want to engage in
what he calls a “high-tech chemical” battle with the rust. For one
thing, he’d have to find a new market. For his pick-your-own
customers, heavily sprayed berries are “an absolute no-no.”
While some experts, like Munck, say it’s unlikely that the
days of Ribes eradication programs will return, given the rising
popularity of growing them among homeowners and small