Chal Landgren, Extension Christmas tree specialist and Oregon State University professor, has a long history of working to benefit the Christmas tree industry. Landgren shared what he’s learned after 40 years of research trials, genetic seed work and problem-solving work with growers.

“The location of your farm makes a huge difference,” said Landgren. “In looking at progeny tests for the past 30 years, if you’ve got a good location and good site, you can probably harvest trees almost two years sooner than a tree grown on a poorer site. The trees that look bad on the poorer site would probably look good on a better site.”

Ideas are the first step in solving many Christmas tree issues. “The best solutions rely on many colleagues and interested growers,” said Landgren. “One of the difficulties is there can be decades or more from when we first identify the problem to when we have operational solutions.” He used the example of genetic sources that require about 10 to 15 years of work before seed is available.

It’s important that growers remain mindful of the consumer’s role – Landgren said it’s easy for growers to get caught up in trying to produce the perfect tree and forget that the tree may weigh too much to haul home or not fit in a consumer’s home.

Landgren discussed several “weird problems” encountered by Christmas tree growers and associated research projects that ensued. “Web blight (rhizoctonia) showed up at three growers’ farms in the Willamette Valley and produced blank spots on trees in the middle of winter,” said Landgren. “We developed some testing strategies with sprays, had one year to do that, then the problem seemingly went away.” He also worked on issues with purple needle eater (Delphinella), which causes regrowth to turn purple and fall off. After two years of control strategies and figuring out which sprays and timing worked, the problem disappeared.

Some experiments weren’t as successful as researchers would have liked. One was a three-year study using drones to inventory fields and check tree health. “It was very exciting, but we were likely too early in the process,” said Landgren. “We crashed the drone and had to jump through a lot of FAA hoops, but we flew over fields and got some wonderful pictures. But I think we were a little too early.” Growers are now using drone technology to do some of what researchers started a few years ago.

Landgren outlined some issues that will likely challenge Christmas tree growers in the future, but assured growers that research is underway to solve problems including current season needle necrosis (CSNN), needle midge, twig weevil, slugs, scarab beetle, rain beetles, annosus root rot and phytophthora.

CSNN has been a problem for as long as Landgren has been involved in the industry. The cause remains somewhat unknown. “It’s under strong genetic control,” he said. “One family of trees will be heavily impacted and the tree next to it is hardly impacted at all.” Site is critical with needle necrosis – firs grown on low elevation bottom land are most often affected. A variety of treatments have been tested, and results show that shade works, calcium chloride sprays helped, but needle shade products have not been consistently effective. “Nordmann and Turkish Fir don’t often have this problem,” said Landgren. “Grand fir gets it regularly.”

Much research has been aimed toward needle midge. Researchers are learning about spray timing, traps, sticky tabs and better scouting. “We’ve learned the best time for spraying,” Landgren said. “There is work going on to control this pest with biologic controls. Growers have contributed to developing degree day models to determine spray timing.” Ongoing work includes testing insecticides and more discernment about the need to spray.

Slugs are a challenging problem – growers can’t ship trees to Hawaii if just one slug is detected. Landgren said researchers conducted trials with water baths to determine whether that treatment killed slugs, but the question became “How long does a tree have to be under water, and how hot should the water be?”

Other slug work involved determining which slugs are in the fields and whether they’re on the ground or in the trees. Research results showed three slug species that result in restricted entry to Hawaii. “If you’re cutting trees, make sure trees are on the ground for a minimum amount of time,” said Landgren. “Keep trees on pallets as long as you can.” Baiting yards may help along with shaking and removing debris from trees.

Phytophthora remains a significant challenge for growers. “The tree will eventually die,” said Landgren. Phytophthora affects water movement in the tree. “We’ve found there’s differential resistance to phytophthora species among commonly planted trees. We’ve also done a lot of identification, so we know which phytophthora species we have and we have better identification tools.” He added that there are few effective controls for phytophthora in field situations, although some nurseries have had success managing it. Improving drainage helps, but phytophthora will be an ongoing problem for many growers.

Annosus root rot occurs primarily when new trees are planted next to old stumps. Better identification tools for this disease help growers detect this problem. Stump removal and grinding along with rotating different species have minimized this issue.

Landgren said progress in managing Swiss needle cast, which he said was a major issue for Douglas fir in the 1980s, is a success story because growers can now identify and manage the problem. “There was significant Christmas tree research at Washington State University and Oregon State University long before it was recognized as a major problem in forests,” he said. “Sprays were tested along with timing and other control strategies.”

Numerous long-term research projects include a study on plant growth regulators to control leader length. “We now have a registered product with consistent results,” said Landgren. “ConShape (from Valent BioScience) is applied when a leader is within two inches of target length.” Affected species include noble, Nordmann and Turkish firs.

Grower problems being studied include when to cut tops, how to straighten tops, using less lethal controls for common aphid problems, seedling survival strategies with dry/hot/long summers, effectiveness of shaking for pest removal, water baths for killing slugs, pests we’re unaware of, winter insecticide sprays not killing yellowjackets, calcium applications, elemental sulfur for controlling Swiss needle cast and whether Moisture-Loc helps trees last longer when cut.

Biocontrols for aphids have been studied, with grand fir as the most often used tree in trials since they have the most aphid damage. Biocontrol agents included lacewings, ladybugs, Aphidoletes midge, Aphidius wasps and Predalure. Researchers also tested biological insecticides and evaluated in-field pollinators with existing pollinator plants to help with biocontrols.

Seedling survival trials were conducted to determine how to help trees survive dry, hot summer weather. Landgren said tree shade products helped, but among all treatments, wood chip mulch at the base of trees was most effective for improving seedling survival.

Nutrient management programs started in the 1980s, a time when growers were guessing about nutrient levels, testing protocols, fertilizer timing and application rates. “Over a five- to six-year period, we developed some effective protocols for Christmas trees,” Landgren said. “After a four-year study looking at greenhouse and field trials, results showed that foliar fertilization was not effective on conifers other than providing some micronutrients.”

He said innovation comes from all corners of the industry, and many of the trials and experiments come from growers. He encouraged growers to remain observant for issues and let Extension know what they’re experiencing.

by Sally Colby