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University of Idaho research tests pest management and biochar in huckleberries

Idaho’s state fruit isn’t commercially produced, nor are there any domesticated huckleberry varieties available.

Native to the Northwest, huckleberries are mostly harvested from wild plants growing within Idaho, Oregon, Washington and Montana public lands.

University of Idaho professor Stephen Cook, head of the Department of Entomology, Plant Pathology and Nematology, has been working to overcome significant hurdles to huckleberry propagation. Cook is in the fourth and final year of USDA-funded research to organically protect greenhouse-raised huckleberry starts from a destructive pest called the black vine weevil, in addition to studying ways to boost survival when those potted plants are transplanted into residential yards or the wild.

The research team also includes Randall Brooks, a University of Idaho Extension forestry professor, and Andrew Nelson, director of the Franklin H. Pitkin Forest Nursery, which is located on the university’s Moscow campus and operated by the College of Natural Resources.

Cook is also leading a second huckleberry project that started in 2022 with funding from a three-year USDA grant. He’ll be testing how the addition of biochar, which is a type of charcoal produced from plant matter, affects huckleberry starts planted in the wild, as well as which pollinating insects are drawn to them.

One of the reasons huckleberries have been so difficult to domesticate is because they are finicky about their growing environment, preferring acidic soils and partial shade. They’re often found in clearings within conifer forests, which have been growing denser due to decades of fire suppression.

“We are starting to see a decline in the stands and the harvest,” Cook said. “Some of that is due to the changing of the forest canopy above them, which may also impact pollinators’ ability to find those plants.”

The Pitkin Forest Nursery, which is Idaho’s state nursery, produces roughly 500 huckleberry plants per year, most of which are purchased directly by homeowners for landscaping. It sustains significant losses in many years to black vine weevils, invaders from Europe that also target many hardwoods, conifers and shrubs propagated at the facility. Weevil larva feed on roots, and greenhouse plants may be unsalvageable by the time they are discovered.

“We’ve had years where we’ve found thousands of them,” Nelson said. “They can easily decimate the crop.”

At the request of regional greenhouse growers, Cook began studying three different organic methods for controlling black vine weevils in the university nursery starting in 2020. Treatments of neem oil, which is an insect growth regulator that prevents immature weevils from moulting, and a type of fungus that attacks weevils both controlled about 85 per cent of the pests in the pots. Introducing a type of nematode that feeds on weevils was the most effective treatment in his study, controlling about 95 per cent of the weevil population. All three treatments are commercially available.

Simulating varying degrees of weevil damage, Cook and Nelson removed 25 per cent, 50 per cent or 75 per cent of biomass from huckleberry starts and planted them outdoors to assess their health and survival.

Cook and his team have also planted huckleberries both with and without biochar added to the soil at the University of Idaho Sandpoint Organic Agriculture Center. Cook hypothesizes that the biochar will lend nutrients and improve soil-moisture retention, boosting survival in a Sandpoint environment with less soil acidity and more direct sunlight than huckleberry bushes can typically endure. They’ll be monitoring survival, plant chemistry and colour of the samples.

The second project, which runs from 2022 through 2025, entails planting greenhouse-raised huckleberry starts adjacent to wild stands throughout Idaho’s northern Panhandle. Cook will plant the greenhouse-raised huckleberry starts with biochar. He’ll be comparing the colour, chemistry and future pollination of transplanted huckleberry plants with the wild ones. Periodically he and his students will be netting insects to identify direct associations with insect pollinators. Cook will keep a close eye on the huckleberry blossoms to determine if biochar causes them to change colour, which could affect insect pollination.