Sunday, January 15, 2012
Q: In a recent column (Nov. 13) you answered a reader who was reluctant to use the herbicide Roundup to combat Japanese anemone. Why? Is it poisonous? I thought it was a salt that got into the plant root and destroyed it. I found it great to control my neighbor's bamboo from invading my yard. I cut the stalk when approximately 18-24 inches tall, then squirt some Roundup down the hole in the stalk. Within a week or so, the bamboo dies. (Until another stalk shoots up!)
A: All pesticides are poisonous to the pests they are intended to kill. And most of them are also poisonous to unintended targets, such as wildlife and humans. The active ingredient in Roundup, glyphosate, is not the most toxic herbicide, but it's responsible for a high number of California pesticide poisoning reports, probably because it is so widely used.
Exposure can cause nausea, sore throat, dizziness and injury to gastrointestinal or respiratory tracts. Eye contact with some formulations causes severe, though temporary, eye problems. Long-term toxicity is still being studied, but there is no longer confidence that it won't cause cancer, mutations or reproductive problems.
Glyphosate is not very toxic to insects but is toxic to aquatic wildlife and amphibians. Some of the inert ingredients that may be used in glyphosate herbicide formulations are much more poisonous to humans and wildlife than the glyphosate itself.
This is a nonselective herbicide, meaning it kills most kinds of plants. Spray that drifts to desirable plants will harm or kill them. It is a "salt" in the chemical sense of a combination of a metal or a base with an acid, but it is not a simple compound like table salt. Instead, it is a complex chemical created to kill plants by preventing the creation of essential amino acids.
A discussion of glyphosate is complicated by the actions of its original patent holder, Monsanto. This company created bioengineered crops that survive Roundup and sells both crop seeds and herbicide. This has resulted in a vast increase of Roundup use, increasing pollution, and aiding the evolution of glyphosate-resistant weeds.
Monsanto's actions have infuriated organic farmers and those who want to eat organic food because the genes that create the resistance have been carried by pollen to organic crops, thus rendering them uncertifiable, and Monsanto even sues those who inadvertently plant contaminated seeds.
Because of its financial interests, Monsanto mounted a vigorous campaign to convince us that Roundup was not an environmental or health hazard. As a garden writer I have been, over the years, bombarded with Monsanto literature about Roundup's virtues and harmlessness. Opponents have also put a great deal of energy into publicizing its hazards. The truth is somewhere in between - there are herbicides with far worse environmental and health hazards, others with less.
I don't think that any herbicide should be necessary in the ordinary care of a garden. Mulching, pulling and digging work fine for most weeds in gardens that get regular maintenance. For weeds growing in cracks of pavement, boiling water can help. There are some "least-toxic" herbicides, such as ones based on clove oil, vinegar or soaps. These kill the tops of plants, but do not translocate to the roots, so perennials tend to regrow after treatment.
Those who use Roundup, or glyphosate herbicide under another brand name, favor it for its low toxicity profile among herbicides that kill the weed root as well as its top. I do not advocate using it; if you do use it, I suggest you follow label directions carefully and also apply it in as small an area as possible, such as by spraying or painting individual plants. Broadcast spraying is more likely to harm unintended creatures.
The most effective nonchemical solution for the invading bamboo would be a 30- to 36-inch deep root barrier made of polypropylene that's 40mm to 60mm thick (roughly 1.5 inches to 2.3 inches thick). After using a rented power tool to dig a trench, angle the top of the barrier farther from the bamboo than the bottom. Install a continuous piece or follow manufacturer's directions for joining pieces tightly. Leave an aboveground lip of 2 to 4 inches. Pack the soil on the bamboo side back in firmly, then concentrate on digging out the disconnected shoots that remain on your side.
If a root barrier is not doable, dig a trench 8 to 10 inches deep and a foot wide at the edge of your property. Fill it with loose mulch and search through it at least twice a year to remove any rhizomes growing into it.
Do note that poisoning bamboo shoots from your neighbor's yard with a translocating herbicide might kill their plants, which could lead to a lawsuit.
Read more: http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2012/01/13/HO811MKQET.DTL#ixzz1jYQZKsdp