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Integrated Weed Management


This garden bed in the Dandenong Ranges has been taken over by a nasty weed known as Oxalis. Unknowing gardeners often accidentally contribute to the spreading of this weed when they attempt to hand weed it; disturbing the bulbils attached to it's roots.

Every garden has them. Nobody wants them. And while some people find them therapeutic to pull out (I know I certainly don't), most of us can agree that our gardens would be better off without them; they are by definition plants growing where they aren't wanted, after all.

But what to do about them? How can we make weeding easier, faster, or less back breaking? How can we make sure those pesky Oxalis stop spreading when we pull them out, and the onion weed stop coming back when I spray it with vinegar? How can we prevent them from making it into our gardens? How can we make our lives easier, and our gardens more beautiful?

“How can we make our lives easier, and our gardens more beautiful?”

Prepare your noggins for what is commonly known in the field of horticulture as "Integrated Weed Management," or IWM for short. Integrated Weed Management is all about combining multiple weed control methods to develop a specially tailored weed management program for a particular site - be it a farm, a production nursery, native re-vegetation area, or in our case, gardens.

Now, for the experienced hobby gardener and horticulturalist alike, a lot of what you are about to read may seem rather simple, but for novices new on their gardening journey, they may take some experience and time to really sink in - but that's okay! Gardening is a journey and even us professionals are still learning day by day. Anyway, there are two main aspects to IWM: weed identification, and weed control methods.

"There are two main aspects to IWM: weed identification, and weed control methods."

Weed identification is difficult - some weeds share common names, some have multiple common names, and the Latin botanical names can be intimidating to even try and pronounce, but it is worth learning to recognize and identify weeds if you want to best be able to control them, prevent them, and just prevent accidently spreading them. All around it is at least worth knowing the life cycle of the weed (annual/ephemeral/biennial vs perennial), when it flowers and goes to seed IN YOUR CLIMATE, its mechanism of spreading, and any specialised structures that help it spread.

Annual and ephemeral weeds will grow to sexual maturity and produce seeds very quickly (often in just weeks), and the saying goes, "1 year of seeds equals 7 years of weeds," but can often be dealt with quicker and easier. Perennial weeds on the other hand can (but not always will) take longer to reach sexual maturity, but often have specialised root systems such as bulbs, corms, tubers, rhizomes, and taproots. Remove the foliage of the weed, but leave one of these bad boys in the earth, and your weed problem will be right back before you know it. This is why those organic herbicide products and home brews will kill some weeds, while others will bounce right back after the foliage dies back.

In turf management there is one more identifying factor to consider: Is the plant a monocotyledon (grass), or a dicotyledon (broadleaf)? While we all want to be as organic as possible nowadays, anyone who has ever tried to maintain a decent sized area of turf to a high quality will know that once the weeds get in, getting rid of them by hand sometimes just isn't always a realistic option (especially as a professional trying to remain competitive), and knowing the different between broadleaf and grass weeds will go a long way when selecting what is known as a selective herbicide.

Now, Armstrong's Landscape and Garden always tries to use preventative cultural methods to prevent weeds in turf, as well as physical control methods like hand weeding to handle small incursions, but when your lovely couch lawn, mown to a precise 30mm, leaves it's winter dormancy with more lawn daisies and dandelions than grass, it might be time to bring in the chemicals. This is where a selective broadleaf herbicide can come in to play. Mixed and applied CORRECTLY (trust me, for the love of all that is holy, trust me on this one), selective broadleaf herbicides will kill dicotyledons (broadleaf plants) while leaving the monocotyledons (grasses) untouched. A word to the wise though: be careful when selecting a selective broadleaf herbicide if you have a buffalo/St Augustine lawn. Some herbicides will also kill buffalo grass.

Poa annua

If only winter grass was as easy as a selective herbicide...

So now that we are all experts at weed identification after reading half a blog post, we can get on with the control methods! There are four main categories of weed control that we will be touching on, and really only three of them are relevant to those of us concerned with gardens:

Physical/mechanical methods: These include hand/tool weeding (digging, hoeing, grubbing, etc), mowing/slashing, grazing, tilling (though some would place this in the cultural category), and installing barriers.

Chemical methods: These methods obviously focuses on the use of herbicides to control weeds, but covers a range of different herbicides (organic and inorganic, contact and systemic, residual and non-residual), as well as methods of applying them such as spraying, ‘drill and fill’, ‘cut and paste’, and weed wicking.

Biological methods: These apply more to Integrated Pest and Disease Management, but still have limited application in weed control. They involve introducing natural predators or diseases to the garden ecosystem to control the selected weed. Some examples are the introduction of rust fungus to blackberries, and a special moth to prickly pear, but these are more the territory of agriculture and land management folks, and less us gardeners.

Cultural methods: These methods are all about the environment we install our garden in, and the way we maintain it to prevent weeds (along with pests, diseases, and disorders). Methods included in this category include mulching, competitive planting/crop competition, and quarantine (for us gardeners this means choosing healthy, weed free plants from nurseries before bringing them home).

Mulch is an example of a cultural method of weed control, and also happens to work wonders to condition and improve soil. Not only that, but freshly mulched garden beds (here a dormant woodland/bulb garden in the Macedon Ranges) look great.

As you can tell, there are plenty of options to deal with weeds, but choosing the right options requires an understanding of the weeds you are combating. Mowing over lawn daisies and dandelions might keep them from going to seed, but certainly won't kill them. Pulling out an oxalis can disturb the bulbils attached to the roots and only serve to further spread the nasty weed. And using organic herbicides or home remedies like salt and vinegar spray will kill annuals like winter grass between your pavers, but will only anger perennial clover in your garden beds (while probably being more toxic to the soil than chemicals like glyphosate, the main active ingredient of the infamous roundup).

"Choosing the right options requires an understanding of the weeds you are combating."

It's important to understand your garden as an ecosystem, and also your neighbourhood as a potential (and almost certain) culprit for blowing in more weed seeds in the wind. What weeds are we getting, and how are they spread (and if possible, prevented)? It may be necessary to either use chemicals, or resort to child slave labour ("who wants McDonalds tonight?!") to get overgrown gardens under control. But once the beds are cleaned up, a slower paced combination of physical and cultural methods can often keep home garden sites under control.

So, using the above cultural, physical, and chemical control methods, how can you take your garden’s weed problem and bring it under your control with an IWM program? What methods can you put in place to keep future maintenance to a minimum, make your garden more attractive, or save your gardeners' backs and give them more time to prune your fruit trees, divide your bulbs, or something else fancy?

I'll leave that one up to you...

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