It’s not always easy to be an organic gardener. Even committed organic gardeners sometimes long to spray herbicide on goutweed or pesky poison ivy. When Japanese beetles or rose chafers arrive in throngs just before your garden party, you may suffer an urge for the good old days — the time before you understood that spraying an insecticide would kill beneficial bugs along with the bad, aggravating your pest problems. But there are also problems that are more easily addressed with organic solutions.
Each winter, the Ecological Landscaping Association (www.ela.org) holds a conference and eco-marketplace where researchers, landscapers, gardeners and environmentalists meet to share knowledge and ideas. This year, one of the presentations I liked best was by Dr. Richard Casagrande of the University of Rhode Island, who spoke on biocontrol of invasive species. He explained that for some problems, organic controls work better than chemical controls.
Casagrande said that when gardeners hear that foreign species of insects have been introduced to help control invasive plants like purple loosestrife, there is a knee-jerk reaction: “Great. And when they’ve finished eating the loosestrife, what’s going to happen next? Will they eat my delphiniums, or my peonies?”
He explained that although people of good will did introduce some evil exotics like kudzu and oriental bittersweet, the process of introducing foreign insects to combat these plants is very tightly controlled. The University of Rhode Island has quarantine labs that are as tightly controlled as the perimeter around the White House.
First, scientists look at how the invasive species performs in its native land. Purple loosestrife came from Europe in the early 1800s, probably in soil used as ballast in ships. But it is not a problem there. Why not? It evolved there, and over time some 120 species of insects learned to love it. Of these, 14 are host-specific, meaning that they don’t eat anything else. A few of these insects were brought to quarantine labs to determine if they eat related species of the target plants, or if they would attack any of our major crops, such as corn, wheat and soy.
If you’ve ever tried to dig out purple loosestrife, you know that it has an amazing root system that will challenge even the strongest back. Scraps of roots left in the ground will start new plants. Not only that, each mature plant produces millions of tiny seeds every year, so even if you did poison or pull a plant, the soil is full of time-release capsules — seeds that will start the process all over again next year, and the year after that, and so forth. Even burning the plants will not solve the problem. But it can be kept under control with the use of introduced beetles.
Since 1994, beetles that eat purple loosestrife have been successfully reducing stands of this exotic. They reduce the number of plants to about 10 percent of pre-introduction levels; as the number of plants drops, so does the number of predator beetles. Similar efforts are under way to control phragmites, that tall grass that has such beautiful plumes in wetlands and roadside ditches.
Casagrande has been using biocontrols to reduce populations of the lily leaf beetle that has been decimating our oriental and Asiatic lilies in recent years. The beetles are so pretty that you might want to use them as earrings: bright red with black trim, about 3/8ths of an inch long. Their larvae, in contrast, are disgusting: They carry their excrement on their backs to deter birds — and organic gardeners. Casagrande and his co-workers have introduced parasitoids from Europe, tiny wasps that reduce the beetle’s population. The parasitoids are doing the job at test sites in Rhode Island and Massachusetts, and are established at release sites in New Hampshire and Maine.
So what can the home gardener do? First, realize that help is on the way in the form of biocontrols. Second, recognize that herbicides for plants and insecticides for beetles ultimately don’t work. Yes, you can kill lily leaf beetles or loosestrife with a spray, but you can’t eliminate them. Third, use pest-resistant species such as ‘Black Beauty,’ a lily that is less attractive to the lily leaf beetle. Lastly, handpick beetles. I handpicked lily leaf beetles twice a day last summer and never saw a larva.
As organic gardeners, we have to accept that we are not in total control of the environment, and that sometimes we have to wait or endure some losses. Biological controls do work. Some exotic pests, like the birch leaf miner, are now nothing more than a minor annoyance, and there are already places where purple loosestrife is no longer a problem. So stay the course — be organic.