If it seems as if pests such as flea beetles are lying in wait for your tender greens to poke their tops above the soil or for you to lovingly plant your seedlings in order to chomp on them ferociously, well, you are not imagining things.
“It’s literally true,” Clay Kirby, an insect specialist with the University of Maine Cooperative Extension said. “They’re waiting for you to plant your seeds and put those seedlings out.”
Battling pests such as the tiny, jumping flea beetle and the large, hungry Japanese beetle is not easy or for the half-hearted gardener. Still, there are things that can be done to try and minimize the damage they do to desired crops without resorting to pesticides, Kirby said.
“You have to bring in a number of tactics to have an overall positive effect with the beetles,” he said. “All of the approaches should be regarded as fitting into an overall battle plan. There is no silver bullet.”
For flea beetles, which feed on leaves and, in their larval stage, roots of the plant, one of the first suggestions he had is to use row covers over seeds and seedlings to act as a barrier. For flea beetles, which are small and quick-moving, he said that the sides of the row covers must be well sealed down so the beetles cannot get into them. This can be done by shoveling dirt over the edges of the fabric or by filling bags with soil and using them to weigh down the edges.
“You’re creating a physical barrier,” Kirby said.
Another option is to plant a “trap crop,” or a crop that the flea beetles particularly like, such as radishes, to attract the pests away from other crops. Once the beetles get there, they can be killed with a botanically-derived insecticide or tilled into the ground. Meanwhile, gardeners can spray kaolin clay on their preferred crops. The clay leaves a whitish residue and makes the foliage less attractive to the flea beetles, Kirby said.
“You can do that in connection with a trap crop,” he said. “You’re pulling them towards the trap crop and pushing them away from your preferred crop. It’s a push-pull system, and it takes some planning.”
Also, Kirby said, if you have a large garden, it might be worth it to physically separate the spring planting from a previous fall crop, because pests can overwinter in crop residue.
“As soon as you harvest a particular crop, you might want to chew it under and Rototill it,” he said. “The flea beetles that are out there now, they’re going to be mating and laying eggs into the root hairs of what’s out there now.”
Some gardeners swear by garlic spray, hot pepper spray or neem oil, which present a barrier between the plant and the pest. Some organic gardeners do use the insecticides spinosad, based on a soil bacterium discovered in an abandoned rum distillery in the 1980s, and pyrethrin, an organic compound that can be derived from chrysanthemum flowers, though it’s a less popular option.
“They’re a last resort tool for a lot of people who would never, ever consider conventional sprays,” Kirby said.
And then there is the Japanese beetle, the iridescent, hungry invasive pest that was first detected in a New Jersey plant nursery a century ago. The Japanese beetles usually start appearing on plants in Maine during the last week of June, Kirby said, tucked away in rugosa rose blossoms. Those beetles, which belong to the scarab beetle family, are a widespread, destructive pest in the eastern part of the country. In Maine, the grubs can damage lawns, pastures and golf courses, while the adults can munch on 400 different species of plants.
“They’re extremely hard to do battle with,” Kirby said. “You can hand pick several times a day for days on end, and it’s still difficult to stay ahead of them. You may just suppress the numbers enough so that your plants have a chance to grow.”
One tip he shared is to pay attention to whether the beetle you are picking has one or more white flecks on its back. Those flecks are eggs of the winsome fly, another Japanese native that is a parasite of Japanese beetles. That fly was introduced in the United States in 1922 in an effort to control the beetles, and kills its hosts a few days after the eggs hatch.
“We want people to preserve that beneficial fly,” Kirby said.
The entomologist does not feel the same way about Japanese beetle attractor traps, which lure beetles using pheromones.
“They draw in more beetles than would normally be there,” he said. “And if people use them, they need to empty them on a regular basis and put them away from the plants you want to protect. I personally don’t use those traps.”
Instead, he goes after beetles the old fashioned way — by picking them one by one off plants and into a coffee can half full of soapy water.
“After a rough day at the lab, it’s therapeutic,” he said.