Planting anything that is guaranteed to attract pests would seem to be the last thing any Maine farmer or homesteader would want to do.
But there are times this counter-intuitive strategy is the best thing for your crops.
The strategy is called trap cropping and it’s based on the fact that pests — like the rest of us — prefer certain foods over others. But if they can’t find their favorite, they are perfectly happy munching on the next best available thing. Unfortunately, that’s often the vegetable or flower you’ve planted for your own enjoyment.
In trap cropping, the idea is to plant those insect-attractive plants as sort of sacrificial offerings or decoys. Ideally, these plants draw the pests away from the crops you’re trying to protect. As the insects gather and concentrate on the trap crop plants, you can either leave them alone to enjoy their feast or dispose of them at your convenience.
“Trap cropping comes under the umbrella of companion planting,” said Kate Garland, horticulturist with the University of Maine Cooperative Extension. “This is when you plant different crops together that benefit each other — trap cropping is one of those approaches of intercropping.”
While using certain plants to draw pests away from other plants can work, Garland did say it tends to be more practical with larger scale plantings.
In smaller plots or gardens, there may not be enough space to plant the trap crops far enough away from the desired crops. In those cases the insects will happily move between the two if they are close together.
“There are a lot of factors to consider with trap cropping,” she said. “You need to figure out whether it makes reasonable sense with the size of the area you are planting.”
It also depends on what you are planting and when.
“Research has shown over and over it can be effective,” Garland said. “The first thing that comes to mind is blue hubbard squash, which is a great trap for striped cucumber beetles and vine borers.”
Those two insects are well known to Maine gardeners and homesteaders and are common pests on squash and pumpkins.
There is also a new eggplant variety that was planted in the University of Maine demonstration garden that turned out to be a bit of a pest magnet.
“It’s called ‘icicle’ and it got hammered by insects at the start of the season,” Garland said. “So we were able to handpick the pests off and then put a cover over the plants.”
Then there is timing to consider.
“Planting an early crop of potatoes that will sprout early can serve as host plants for the first generation of potato beetles,” Garland said. “Then you can eradicate [the beetles] on those early plantings in time to plant your main potato crop later.”
Placing the trap crops around the perimeter of the garden can help, according to Garland.
Concentrating the pests in that area can save time and money and allow you to control the pests more effectively.
“You can then manage the pests by hand picking them or using a systemic pesticide or some organic control just in the trap crop area,” she said. “So it can save you from having to spray or hand pick [the pests] from an entire field.”
Trap crops that could be useful in Maine include dill that attracts tomato hornworms, radishes to attract cabbage maggots and nasturtiums to attract aphids.
Garland does caution that, while trap cropping can work, it’s not for everyone.
“I don’t want to get people’s hopes up that it will be effective on its own on a homeowner gardener’s scale,” she said. “It could be one of the tools for pest control, but it’s not a whiz-bang solution.”