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Biological Controls

It’s not always easy to be an organic gardener. Even committed organic gardeners sometimes long to spray herbicide on gout weed or that pesky poison ivy. There are times when Japanese beetles or rose chafers arrive in throngs just before your garden party and you want to nuke those nasty critters. There may be times when you have an urge for the good old days, the time before you understood that spraying an insecticide kills beneficial bugs along with the bad, aggravating your pest problems. But there are also problems that are more easily addressed with organic solutions.

Purple loosestrife

Right now purple loosestrife is blooming in swamps and along streams and roadsides. It is a tall, beautiful weed with small purple-pink flowers growing on square stems. So who can object to such a pretty plant? Biologists know that it is a plant that came from Europe and has few natural predators here to keep it from taking over wetlands. It has an amazingly robust root system and can elbow out native plants, in part, because it produces huge numbers of seeds. Not only that, the plant offers little of food value to our wildlife. It’s pretty, but worthless. A thug.

Purple loosestrife came from Europe in the early 1800’s –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 eat it. Of these, 14 are host specific, meaning that they eat it – but nothing else. A few of these insects were brought to quarantine labs to test the following: Will they eat related species of the target plants, or plants that share a habitat? Will they attack any of our major crops such as corn, wheat and soy? Beetles have been found to help control purple loosestrife.

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 many thousand tiny seeds every year, so even if you did poison or pull one, the soil if full of tiny time-release capsules – seeds –  that will start the process all over again next year, and the year after that, and so forth. 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 numbers of plants to around 10% of pre-introduction levels; as the numbers of plants drop, so do the number of the predator beetles.

Dr. Casagrande and his colleagues at the University of Rhode Island have been working on finding and introducing biological controls for major plant and insect pests. But it is a slow process. They have introduced 3 parasitic wasps to control the dreaded lily leaf beetle, that red pest that devours our Oriental and Asiatic lilies. When I asked him recently how the wasps are doing, he told me that they are well established in sites in Rhode Island, Massachusetts, New Hampshire and Vermont. That some have spread as much as 10 miles since introduction. However, the predator insects are not for sale – so we just have to wait for them to slowly make the way to our gardens.

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. Patience is required as Mother Nature, with a little help from scientists, will eventually restore balance.

I have purple loosestrife near my stream. My control? I cut it down with my pruning shears, thus preventing the plant from producing seeds. When small plants appear in my flower gardens, as they have done, I dig them out before they establish a big root system.

Angel's Trumpet or Datura

I have given up planting Oriental and Asiatic lilies. Dr. Casagrande told me that there are a few cultivars of lilies that are less attractive to the pest beetles, such as ‘Black Beauty’. But instead of those lilies I now grow a lovely unrelated plant called angel’s trumpet (Datura spp.). The flowers are big white trumpets not unlike the lilies, but they bloom in sequence all summer, sometimes a dozen or more at a time. It’s an annual here that I re-plant every year. One note of caution: the seeds are poisonous if eaten.

As an organic gardener, I have to accept that I am not in total control of the environment and that sometimes I have to endure some losses. Biological controls do work, and have made some exotic pests such as birch leafminers into nothing more than minor annoyances. There are already places where purple loosestrife is no longer a problem.  I urge you to stay the course and be organic.