May 162012

Whilst recognizing that using cultural methods for weed control rather than reaching for the herbicide is better for the environment, there are times when things just get out of control. At this point one tends to look for a herbicide. The shelves of some nurseries are hardware stores are lined with bottles promising all sorts of wonderful results. The trick is to use something which will both do the job and do the least harm, or better yet – no harm.

Probably the most widely used herbicide by the home gardener these days is glyphosate. Originally marketed as Roundup™, now the patent has ended glyphosate is marketed under many names and is readily available in various concentrations and applicators.

Glyphosate is extremely useful to the home gardener. It is considered to be relatively low in toxicity and have no carcinogenic effects, so it is safe to use in the home garden. However it is not necessarily safe for your plants. Just about every nursery person in retail has had a customer bring in a weirdly distorted stem of a rose bush and ask what is wrong – the answer is glyphosate spray drift – and it is not reversible – you are now looking at an ex-rose. Glyphosate is a non-selective herbicide; this means it will generally kill what plant life it lands on. There are a lot of exceptions, but as a rule of thumb in the home garden, expect it to kill what it hits.

Also be aware that glyphosate is extremely toxic to aquatic life, and when it runs into streams and waterways, it isn’t denatured just diluted and concentrations as low at 10ppm can kill fish. Nor is it good for your soil. It is reported to be quite toxic to the beneficial soil micro-organisms – those very things you have spent so long encouraging and nurturing by digging in compost and manures. Frustrating!

That said, you can still use glyphosate, just use it sensibly. Spray on a still day when no rain is forecast. Spray to the point of run off. Think about this. Do not spray until it runs dripping off the leaves, because then it has run off the plant. Spray until it is like a fine mist coating the plant. This way you get the best coverage on the plant, use the least amount of herbicide and protect both other plants and the soil.

There are relatively mild selective herbicides which can be used to kill broad-leafed weeds such as bindii, clover, oxalis, dandelion, and thistles. These use various active ingredients such as Bromoxynil Octanoate, MCPA (2-ethylhexyl ester) and DICAMBA. Use these with care and take note of any with-holding periods (e.g. keep chooks and pets off sprayed lawns for a certain period of time).

Alternatively you can use acetic acid (main component of vinegar) and salt sprays as a non- selective herbicides – best used for weeds with large flat leaves, also controls algae, liverwort and moss.

When using herbicides, use common sense, use the minimal amount to do the job, use when the plant is actively growing, and spray on a still day. Use protective clothing and wash up thoroughly afterwards.