A Cinara aphid colony on a Christmas tree. Photo courtesy of NYSIPM

by Courtney Llewellyn

Pest management is an ongoing battle for all growers, but Christmas tree growers have their own war to wage. Fortunately, in New York State they have researchers at Cornell University and NYSIPM to back them up. Betsy Lamb and Brian Eshenaur of NYSIPM recently updated growers on what to be on the lookout for in 2021.

The first pest discussed was the Cinara aphid, which Lamb said she had never seen before this year. Per their scouting, they seem to be increasing in frequency – one grower outside Ithaca said they were a very big issue this last holiday season, but they had no idea how they ended up on their farm. Cinara aphids usually don’t harm trees, but they are unwelcome guests of customers who bring infested Christmas trees home. Looking a little like ticks, their colonies live on the trunks of trees and they feed late in the season. Autumn scouting is important for this emerging pest, and growers can look for sooty mold and wasps to find Cinara aphids. There are no specific treatments for the pest as of yet.

Another pest that appears to be common at the moment is the gypsy moth, which is being spotted through the Finger Lakes and Southern Tier regions. They cycle about every five to seven years, and hatch en masse. Lamb said it’s important to scout for them now, as they become active starting in late April. If you find egg masses, remove them, but don’t just drop them on the ground. Bt products work on small larvae.

“Last year they hatched in May; their lifecycle ends in August, so that gives you a long time to scout,” Eshenaur said. “There are two diseases that affect them, and if there’s a lot of wet weather, that helps to knock them out. Even if you’re not seeing them now, they can pop up in other parts of the state. Pay attention to what’s around your field too.”

They noted growers want to be on the lookout for spotted lanternfly too, which has been seen in the Finger Lakes and downstate. “They’re not going to be consuming your Christmas tree but they could create problems when shipping – or if egg masses are on trees, they could hatch in homes,” he added.

Plant pests to watch for include horsenettle and horseweed (or marestail). “For Christmas tree growers, glyphosate is kind of your go-to year after year, and that almost increases the development of weeds that are resistant,” Lamb cautioned.

And there are also animal pests to consider – especially deer. Eshenaur reviewed some deer repellent trial data from 2019-21 using Plantskyyd and TRICO repellents. Plantskyyd (made of dried blood) provides intermediate control but it’s hard to use, Eshenaur said. TRICO, which uses sheep fat as its active ingredient, just received U.S. approval, which he said means New York won’t be far behind. It showed a lot of promise in trials.

When scouting for issues in Christmas trees, consider what other trees near an affected tree look like, how widespread an issue appears to be, when the issue appeared and what the weather’s been like. If you end up sending a sample to a lab, make sure you take dead needles as well as green needles from nearby, along with pictures of the area. Being proactive now means a better holiday season down the road.