There are natural ways to kill your weeds

Thu, 09/27/2018 - 4:45pm

In these times, when America’s most popular chemical weed-killer, Roundup, is undergoing more scrutiny and Block Island looks for a means of eliminating its use, it’s a good time to look into more natural solutions.

One of the hallmarks of late autumn is the unmistakable smell of vinegar emanating from the wet leaves lying rotting on the ground. Fermentation and oxidation of natural carbohydrates results in a dilute form (5 percent) of acetic acid, which we commonly call vinegar. Can we take this process of decay and use it to our advantage? Well, we can at least try.

Vinegar is both antibacterial and anti-fungal and it is no wonder then that vinegar is the primary component in many do-it-yourself household cleaners. It’s also the primary component in one of the most popular home-made weed killers, which also contains salt and dishwashing liquid. Recipes may vary, but a common one is one half-gallon white vinegar, one-half cup salt, and two tablespoons of dishwashing liquid.

We all know how devastating salt can be to foliage. After a good (or bad, depending on how you look at it) Block Island storm, evidence of salt spray is everywhere, shriveling the leaves of many plants. And what does the dishwashing liquid do? According to it “works to break down the protective coating on the leaves and allows the salt and vinegar to completely dehydrate the plant.”

This mixture works best on a hot, sunny day when plants may already be under stress, and several applications may be necessary to really beat back the weeds. Just sprinkle it on the weeds with a watering can.

Another, simpler method of weed control is to use boiling water. I’ve never tried this, but if it weren’t raining right now, I would be putting on the kettle and then going out to try this on some black swallow-wort.

In fact, I would be trying both methods, side by side, as a means of comparison. 

It’s an experiment worth trying because presently the only safe way to get rid of this most noxious and pernicious weed, that I know of, is to completely dig it up. If one looks at the infestation of this invasive plant in fields and along roadsides on Block Island, that seems like a Herculean task. 

And then there’s Sisyphus — the figure in Greek mythology tasked with rolling a boulder up a hill, only to have it roll back down. Again and again. Why, because not only does black swallow-wort, a type of milkweed, seem impossible to kill, it produces thousands of winged seeds that catch the wind and travel all over the place. 

If you have black swallow-wort in your yard, this is the most important time of year to address it — not necessarily to actually kill the plant, but to prevent the spread of those seeds. The pods are starting to open now, so if you can at least cut them off you will be doing yourself and your neighbors downwind a favor. Be careful of how you dispose of the seed pods. Don’t just dump them into your compost pile, but instead secure them in a sealed container with some liquid so they will drown and rot. 

The reason plants from foreign places become invasive is because they have no natural enemies here to contain them. There has been a biological control for black and pale swallow-wort in the works since 2005, and it was just approved by the U.S. Department of Agriculture in August 2017 for field testing.

To find a biological control, researchers usually go back to the area where the plant originated — in this case, Hungary, and then try to find a species — usually some type of insect  that uses that plant, and only that plant, as its “host.” It can take years of research and testing to make sure no native plants will be affected. The idea is that because of the symbiotic relationship between the host plant and the insect, once the plant dies off, so will the insects. 

The biological control currently being tested for black swallow-wort is a moth called Hypena opulenta, and the University of Rhode Island has been instrumental in its discovery, rearing, and use. Currently the field testing is being conducted in Charlestown, R.I. and on the island Naushon, in Massachusetts, where the moth was released in controlled cages. Results are not yet in, (it’s too early to tell)but there is hope for its success.