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.
There are many definitions of IPM, but Sidebottom likes this one: IPM is a strategy for keeping plant damage within bounds by carefully monitoring crops, predicting trouble before it happens and selecting the appropriate control – biological, cultural or chemical, if necessary.
Another way to describe IPM is “socially acceptable, environmentally responsible and economically practical for crop production.” “That’s where I like to see IPM,” Sidebottom said. “If it isn’t practical, what good is it?”
The goal of IPM is getting to harvest with limited pest damage, without costing a fortune and without environmental damage. Sidebottom said the last item is important because younger consumers pay close attention to environmental issues. Confidence is also an important aspect of IPM – knowing what you’re spraying for, and knowing whether it works.
“Thirty years ago, we didn’t know anything about rosette bud, scale or rust mites,” said Sidebottom. “We have more pests, but we’ve reduced pesticide use.” IPM has helped growers deal with pests with varying success, but what issues will growers be dealing with in the next 20 years?
Many pests are becoming regulatory pests, which doesn’t bode well for IPM because it means zero tolerance. Millennials, Gen Z and pesticides don’t mix well – young people are more familiar with what’s used on plant material, and often have negative perceptions about commonly used products. Pesticide regulations, including the loss of chemistries growers have relied on for years, is another challenge for IPM.
Pesticide resistance is an IPM issue that isn’t going away. Sidebottom cited the example of growers using bifenthrin (Sniper) and not getting good control of twig aphid. “There’s only so many times we can say ‘you put it on wrong’ or ‘it rained’ or ‘you didn’t get good enough coverage,’” she said.
The number one practice that affects pest populations is interplanting. Sidebottom suggested finding a way to manage inventory to avoid the practice of interplanting and the pests that come with it. A project at NC State involved collecting aphids from various farms, placing them in a petri dish and using different amounts of bifenthrin to see which aphids were killed.
“They calculated the LD 50 – the lethal concentration at which 50% would die,” said Sidebottom, adding that research results are preliminary. “Results are for four-hour analysis rather than 24 or 48 hours, but in most analyses, the label-rated bifenthrin, which is 3.2 ounces of active ingredient per acre, had two or three resistant populations. So there are definitely some populations of twig aphids that have become resistant to bifenthrin.”
Sidebottom said the grower with resistant aphids had interplanted, which means populations weren’t wiped out and the reset button wasn’t pushed. “With the more resistant aphids, if you aren’t continually dumping chemical on them, they would probably die out of the population because they’re less fit,” she said. “So don’t interplant, but also don’t continue to use the same chemistry from one year to the next. We don’t have a lot of chemistry out there – there isn’t a lot we can rotate to.”
For IPM in the future, the wild card is climate change. “We don’t really know how it’s going to affect us,” Sidebottom said. “In forestry genetics we talk about building resilient trees so those trees can withstand drought, too much water or high temperatures. We don’t know how climate change will play out, but we’ve always had to deal with weather, and bugs don’t have calendars.”
What changes in pest control are likely due to weather? Sidebottom has been tracking twig aphid hatch and has seen hatch occur two to three weeks earlier over the past five or six years compared to previous years. “But I see more parasitism,” she said. “That little wasp lays its eggs in scale and survives in scale all winter long. I think when we’ve had warm thaws in fall, it has allowed the wasp to survive better, and we’re having better biological control.”
For Christmas trees, cultural practices are an important aspect of IPM. But scouting is also critical. “That’s your steering wheel,” said Sidebottom. “That helps you decide what to do, and whether it works or not. The insecticides are the smallest portion, and only used if necessary.”
IPM for Christmas trees should involve both cultural practices, such as ground cover management, and site selection. Prescription fertility management and plant tissue samples are also part of IPM. Protecting natural enemies is critical – think about pesticide choices and be slower to pull the trigger on chemistry use.
For effective pesticide application, Sidebottom said the hammer often has to come down hard. “Sometimes you don’t need to worry about the natural predators,” she said. “If you need to get control, you need to get control. The only way you aren’t wasting money is if you get good coverage, put it out on a day that isn’t windy and it isn’t going to rain in a couple of hours – be smart about what you do.”
“Pests always change,” said Sidebottom, “but the principles of control never change. They’re solid principles and will get you back on the winning side.”