How to control those pesky weeds

Last week, I confessed that my garden was not in the immaculate weed-free state I would hope for it to be – or that you might expect from a weed scientist.

Today let’s talk about some options for controlling them. That is, if you are in the same state as me. And if you haven’t yet subscribed to the “if you can’t beat ’em, eat ’em” (or use them as dye) theory.

For the past three years I have taught the lab section of the “Weed Biology and Control” class at Utah State University where we spend the first five lab sections learning plant (weed) identification and the remaining seven lab periods are focused on different aspects of managing the weeds. We cover everything from mechanical to chemical control options, their different effects on the environment, to how to detect and mitigate injury symptoms (from either mechanical or chemical treatments). Obviously that’s way too much information to try and fit into one blog post, so for now we’ll just speak of generalities.

How you go about managing those pesky weeds has a lot to do with which weeds are giving you trouble. Knowing your enemy comes in handy in these situations. Annual weeds (those that complete their life cycle in one year or growing season), for example, are generally really good candidates for mechanical/physical control because if you pull them out or mow them down before they set seed they won’t be coming back from the roots. Perennial weeds (those that keep on coming back year after year), on the other hand, have lots of energy stored in their roots so unless you mow them back continuously or pull the whole root system out they will just keep coming back. So knowing what it is you’re trying to control, and a little bit about it, is a vital first step.

Once you know a little bit about what you’re dealing with, you can start exploring your control options. We can lump weed control methods into three general categories: mechanical/physical, chemical, and biological. Let’s take a look at what each of those means and some of their advantages and disadvantages.

Mechanical/Physical Control

This can include everything from hand pulling weeds, to using a tiller, to burning, or to smothering (like you would with a mulch) or flooding.

If you’re like my grandpa, you plant your vegetable garden in nice straight rows with enough space between each row to get the tiller through them. Though he has to do this multiple times throughout the summer, having a tiller do the work makes it go pretty quick. The two main disadvantages to this are: moisture loss from the soil due to frequent disturbance, and tilling can bring new weed seeds to the surface where they can grow or spread other weeds around to keep growing.

If you’re like me, you don’t think about the spacing between your rows, so instead of being able to remove the weeds with a tiller, you have to use a hoe or your hands. Because my garden isn’t terribly large, this really isn’t so bad (if I stay on top of it). Sure it takes more time, but I can fit more plants into a bit smaller space.

Mulches can be great at keeping weeds down, but unfortunately they can also be great and introducing new weeds. If you are using straw as a mulch you’ll want to make sure it comes from a reputable source so you’re not bringing in a whole bunch of new weeds with it. I know that plastic mulches are common; you know, the sheets of black plastic that people lay down and then poke holes through to plant into and then they might cover the whole thing with a bark mulch to make it look nice? But, frankly, I would stay away from them. Anywhere you have a hole poked through for one of your garden plants, you can bet that the weeds will come through there as well. They also make great water barriers – which isn’t a good thing for your plants that need to be watered. So unless you install drip irrigation along with the plastic mulch it’s going to be a lot harder to get your plants the water they need.

Chemical Control

A lot of people get up in arms about chemical control, and while I can see why at times, I will say that I believe they have their place. Chemicals are very effective, and if you make sure to read the labels you should have effective control with little to no non-target effects, and it should need few (if any) repeat applications. The obvious disadvantages are: risk of non-target injury or death if you don’t properly follow the label instructions, potential risks to human and environmental health if you don’t properly follow the label instructions. But, if you do follow the label, those risks will be at a minimum and you can enjoy a weed free existence. At least in your garden and/or lawn.

Once again, you’ll need to know a little something about the weeds you are trying to control. Some chemicals are considered “broad spectrum”, meaning that they are indiscriminate killers. So, while it will kill the dandelions in your lawn, if you also get it all over your grass, the lawn will be injured (or killed). It may do a great job and killing that bindweed, but know that if you also get it on your rose bush, the rose bush will be injured (or killed).

Others are considered “selective”, meaning they selectively kill certain plants. For example, it will kill the dandelions in your lawn, but will leave the grass unscathed. Or it will selectively kill newly germinating plants, but already established ones will be fine.

And, just to be clear, organic weed control can include use of chemicals. For example: acetic acid (people always liken it to vinegar, but it’s much much stronger than what you are putting on your salad) is used as an herbicide in organic farming. That homemade weed spray you found on pinterest? Full of chemicals (because, yes, soap and vinegar are considered chemicals). So, just remember that just because something is “organic” doesn’t mean that herbicides haven’t been used – it’s just a difference in the types of herbicides that are allowed.

Biological

Most of the examples of biological control that I can think of wouldn’t be applicable to your home setting, but rather a larger landscape approach to controlling invasive plants. However, there is one possibility if you have more than just a city-lot sized home and garden: goats. Goats are great at controlling weeds because they eat pretty much anything. But, that’s also their main disadvantage – they eat pretty much everything. So if you decide to use goats as a weed control method, you’ll definitely need to keep them on a short leash to make sure they aren’t getting into your prized cabbages or anything.


Which weeds are your biggest problems? What is your favorite (or least favorite) way to control weeds?

Like I said, there’s too much to cover in just one blog post, so let me know what weeds are on your hit-list and we can talk about specifics.

4 Comments

  1. Prized cabbages! 😂 Love!

  2. I would like to better manage the weeds in my lawn this year and have not used any chemical controls in the past. Thus the weeds are starting to spread and are rather noticeable. A friend told me that I have a lot of creeping Charlie, which he said is impossible to get rid of. Please give me some advice, as I do not want to do a lot of spraying. You likely are having problems with easy-to-identify broadleaf weeds such as dandelion, clover, violet and henbit that have broad leaves instead of grasslike blades. Dandelions are flowering yellow now and are very common in lawns. For small weed infestations, you can manually remove them using a weeder. It is best to remove as much of the root system as possible while minimizing disruption to the lawn. This method is not very practical for controlling large weed populations or weeds like clover that are intertwined with the lawn and very difficult to pull out.

    • Heather

      August 4, 2016 at 8:53 am

      Hi Jay, creeping Charlie is a difficult weed to manage in a lawn – especially without chemicals. You’re right in that it can’t be removed the same (or as easily) as dandelions by digging it up. The best way to combat it is to make sure your lawn is healthy – proper irrigation, mowing height, aeration, and fertilization – because a healthy lawn is actually very competitive against weeds. You can ask your local extension agent on best practices and grass types for your area. If you aren’t completely opposed to chemicals, you could achieve reasonable control of the creeping charlie by applying a 2,4-d or dicamba herbicide, and then focusing on the cultural practices I just mentioned. Good luck!

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