Keeping deer out of Christmas tree plantations, especially from late autumn and through winter, is a perennial problem. Bucks mark territory by rubbing trees, and both bucks and does are attracted to trees as a food source.
With ample food, deer quickly develop high populations, which leads to heavy browse damage year-round. They’re also major hosts for ticks, putting many at risk for tick-borne diseases.
Richard Cowles, Valley Laboratory, Connecticut Agricultural Experiment Station, said growers can experience extraordinary crop losses when deer populations are high.
“It’s the interaction between deer population density and how much alternative food is available in winter,” he said. “They eat everything they can reach through winter, including Christmas trees. We’re trying to prevent constant winter browsing that ruins Christmas trees.”
While repellents are effective, Cowles said they shouldn’t be considered a stand-alone method for managing deer browsing. “If deer are hungry, deer will feed on repellent-treated trees,” he said. “There has to be an alternative food in the perimeter. Provide something that’s palatable and nutritious to deer outside of what you’ve treated with repellent to prevent deer from becoming so hungry that they feed on the repellent-treated crop.”
Classic animal repellent products are either toxic or taste bad. Fungicides, soaps and malodorous products such as egg solids, dried blood and processed sewage sludge are sometimes used to repel deer. While these products are effective repellents, they break down quickly. A spray application in November may only offer a short window of protection and not through winter when it’s needed most.
Fatty acid repellents were tested in a Cornell University trial that took place in Onondaga and Allegheny counties in New York. Researchers found that while Plantskydd® repellent worked well initially, effectiveness declined over winter. The trial also tested lanolin-based Trico® Pro and found that one application deterred deer fairly well through winter.
The idea for a lanolin-based repellent is based on the European tradition of using raw sheep’s wool wrapped around leaders to prevent deer browse. It works because deer are repelled by the odor of raw sheep’s wool, which contains lanolin.
Cowles explained that when fat products are sprayed onto leaf surfaces, compounds move into the plant cuticle. “One of the advantages of using repellents like this is they are resistant to being washed off with rain,” he said. “We don’t know the ecological significance of these odors to deer – all we know from their response is they are repugnant to deer.”
Focusing on excluding does will help keep out bucks as well.
It’s legal for growers to make their own deer repellent as long as it’s used only on their own property and not sold to others or sold as a service for custom application. If a product or service is sold, federal law requires the product have a label.
The two ingredients needed for the lanolin emulsion can be purchased online. Cowles provided the simple recipe for deer repellent: five parts of lanolin, one part 30% sodium lauryl sulfate and four parts hot water to make a 10-fold concentrate. Mix well in a blender or use a drill-driven stirring device in a five-gallon bucket.
“Lanolin forms an emulsion well with water dispersed within it,” said Cowles. “It’s better to make a highly concentrated lanolin product – it’s very stable and can be stored for weeks or months.”
After making the concentrate, mix with water 10:1 before using. Cowles said it’s difficult to spray as little as 2.5 gallons/acre, so growers can dilute further to make 20 gallons.
At about $8/lb. for lanolin, the cost of making a 5% emulsion equivalent to the commercial product Trico Pro would be about $7/acre. Sprayable emulsions made with refined lanolin and other fats are long-lasting repellents. Cowles said such emulsions have little odor to humans, are biodegradable and have negligible environmental impact. They’re a cost-effective option to protect valued ornamental plants and Christmas trees.
The mixture can be sprayed at any time of year if it’s kept warm (at about 70º F or warmer). If it’s extremely cold outside and the mixture gets too cold, the emulsion may plug nozzles. Cowles said if the temperature is below 65º, 30% sodium lauryl sulfate will solidify, so be aware of the temperature in storage. To avoid clogging, he uses a gravity-feed backpack mist sprayer with a large orifice.
“When you mix a lanolin-based repellent, mix it right before spraying,” said Cowles. “Start with warm water to avoid curdling. I like to apply a deer repellent in fall to exclude does from Christmas tree plantings. If does are not active within Christmas trees, then bucks won’t come into the area either. Start by excluding does before the buck rub season to prevent buck rubbing.”
Fat-based repellents serve as an odor fence that keeps deer away. “If you have a wide enough perimeter treatment on a large field,” said Cowles, “it’s equivalent to treating the entire field. From our observation of deer behavior, it should work. Within a couple days [of application] I would challenge anyone to detect the odor. I’m not concerned about residue affecting consumer preference.”
Regarding residual odor, Cowles said lanolin has a very faint odor, reminiscent of a damp wool sweater. “I like to think of it as applying eau de sheep – applying a little bit of sheep-scented perfume to Christmas trees,” he said. “An incredibly small volume of this odor repels deer.”
While most aspects of using lanolin are positive, Cowles said it’s difficult to clean spray equipment after using lanolin products. Growers should plan ahead to have hot water for a final stripping of the lanolin from the sprayer interior and screens. Limonene (citrus) works well as a lanolin solvent. He also cautioned that any aerosolized fatty materials can cause lung injury if inhaled.
Deer repellents shouldn’t be relied on as a stand-alone measure unless the deer population is low. “Fencing is the gold standard for protecting trees,” said Cowles. “Consider reducing deer populations through hunting. Many growers provide alternative food such as clover planted as a ground cover.”
by Sally Colby
