by Sally Colby
Dr. Jill Sidebottom, North Carolina State University has seen a lot of changes in Christmas tree production over the years, and said in changes yet to come, IPM will be more critical than ever.
According to Sidebottom, the number one issue in growing Christmas trees in North America is that the majority of trees aren’t grown in their native area. “There are very few species of Christmas trees that would be growing where they are growing if people hadn’t planted them,” she said. “Eastern white pine is native to the mountains in North Carolina, but we don’t grow it there because you can’t sell it. They try to grow it in the eastern part of the state where it’s never supposed to be, but they can sell it so they try.”
“Don’t have bare ground; keep the soil cool. There’s less stress on trees,” Sidebottom said. “You get better root development as long as there’s no grass.” When grass is eliminated, there’s reduced competition for nutrients. A switch to clover makes sense because clover is naturally Roundup-ready. “It gives nitrogen through the year that will allow trees to grow, but not a big dump of nitrogen that makes the bugs happy.”
Sidebottom said nitrogen is like candy to bugs. Pests that increase with more fertilization include the ones that cause issues, including twig aphids, white mites, white scale and balsam wooly adelgid. “You want trees to grow as fast as possible, but IPM is a balancing act,” she said. “Sometimes you may fertilize more or less, but understand how that affects the whole system.”
Obtaining good groundcover can happen several ways. Sidebottom suggested chemical mowing with low rates of Roundup applied over the top at eight ounces/acre, then reducing to four ounces/acre when new growth is out, making up to three applications each year. Any remaining problems should be cleaned up in autumn.
Another alternative is to allow field borders to grow up, which allows more natural plants to come in around the edges. “For marketing, plant a pollinator garden,” said Sidebottom. “The garden won’t be there when you’re cutting trees, but you can put a sign up and say, ‘This is my monarch garden.’”
Sidebottom advised growers to take photos of findings during scouting, such as a monarch caterpillar feeding on milkweed, and use those photos on social media. “Take pictures, have signage on your farm,” she said. “Plant flowering borders with red clover, sunflowers, milkweed, yarrow. Herbs are also great for attracting predators.”
Scouting is essential. Sidebottom recommended growers make time for it and train employees to do it properly. It’s worth purchasing a good 7x hand lens – with higher magnification, the field of vision becomes smaller. Scouting should involve looking at trees for signs of disease and pests – a crooked top might mean balsam wooly adelgid. “You might find mottling,” she said. “Any time you see mottling, look to see what’s causing it. We beat our trees to look for twig aphids in spring. It’s also good to pull off a shoot and look at the front and back with a good hand lens to look for mites or scales.”
Sidebottom also advised growers to scout for the good guys, such as ladybug larvae. “You probably won’t see as many predators in high numbers,” she said, adding that one adult ladybug can eat at least 200 aphids. “If you see any, that’s good – natural controls are coming in.”
Sidebottom encouraged growers to determine their IPM superpower and which practices to be proud of on their farm. Scouting, groundcover management, cultural practices, recordkeeping, biological control and quality control are all components of good IPM and provide a valid reason for growers to stand behind what they produce.