How to spray weeds effectively

Author: Stefan Palm   Date Posted: 24 April 2024 

As a proud lawn owner, there will no doubt be times when you have to spray chemicals to keep out unwanted weeds and pests. Often your spraying efforts can be hit and miss with mixed results. So how do you spray effectively every time?

The same chemical, applied in the same way, doesn’t necessarily achieve the same results. I’ve heard customers say time and time again that certain herbicides don’t work. This week while consulting, I listened to a customer tell me that they had removed and replaced their whole lawn due to a weed problem that they could not get on top of.  While I understand the reasons people say this, I also know that there are many factors that determine how successful your efforts are. What can seem like random results are not so much a result of the efficacy of the chemical but rather a bunch of other factors that can play havoc with how well they work. Let me explain.

Choose the right product. 

There are many products that will selectively control weeds in lawns. The type you choose depends on the lawn you are spraying and the weeds you have in it. Typically, there are selective herbicides for winter grasses, summer grasses and broadleaf weeds. (click through for more info)  For example, if you choose a broadleaf herbicide and are targeting winter grass, you won’t get the results you are looking for. When going out to buy a herbicide, go prepared by knowing the weed you're targeting. Look for the weed on the label of the herbicide you buy. Alternatively, take a sample of the weed with you or do some online research so that you can have it identified before purchasing. Ensure that the chemical you buy is suitable for the lawn you have. For instance, some selective herbicides are not suitable for buffalo lawns. If you apply a weed and feed type product (containing dicamba) on a buffalo lawn, you’ll most likely kill it.

Read the instructions

It is critical to thoroughly read the instructions of the chemical you intend to use before you open and use it. Instructions are printed on the packaging. While this may take a bit of time, it will give you a much better chance of success.  The label will tell you exactly how much chemical to mix, how much water to mix it with and how much lawn area that mix should cover. All these factors are very important when applying chemicals to your lawn. I often hear stories of people who have mixed "a little extra" chemical into the batch with the thought that this will give better results. Nothing could be further from the truth. My advice is to follow the instructions to the letter. The label will also give you advice on:

  • What safety gear you should use. Eg, gloves and goggles etc
  • What to do if you ingest any or experience some skin contact
  • Things to avoid. For example. some chemicals should be kept away from waterways  

Use a wetter and spreader

This is an often overlooked step. Applying a wetter and spreader breaks down the surface tension of the droplets that come out of the sprayer. This ensures a more even and complete coverage over the weed, giving you better results. They also help the chemical to stick onto the weed. This is a critical step for tough weeds like creeping oxalis and clover.

Choose the right weather conditions

Some chemicals will not work if exposed to dew, rain or water directly after application. It is also advisable not to spray in windy conditions to avoid off-target damage or spray drift onto nearby plants.  In some instances, warmer weather provides more favourable conditions than cold weather for best results.

Have the right spray equipment at hand

Good quality spray equipment is critical for the best results. The most common type of home spray equipment is a hand pump pressure sprayer. Most people have had experience with one of these and some point in their gardening career. The only issue with these types of sprayers is that they are inconsistent with their spray pressure. When they are freshly pumped up, they spray at higher volumes due to the higher pressure. As the pressure depletes in the course of spraying, so does the volume of chemicals being emitted until you have to pump them up again. This constantly variable spray volume will result in varied results.  While this type of sprayer will do the job, there is a range of rechargeable battery sprayers that have come onto the market in recent years. They come in various sizes but, more importantly, spray at constant pressure, giving a much more consistent result. I can recommend Solo battery sprayers. They aren't cheap, but they are a quality unit and do a great job

Don’t spot spray

I would recommend spraying your whole lawn rather than spot spraying. Spot spraying can lead to applying too much chemical being applied to each weed (which can burn the lawn), and it can lead to only spraying part of the weed. Often creeping weeds spread out over a large area, and it’s easy to miss parts of the weed if you’re spot spraying, leaving the missed parts to continue on their merry way. 

Don't mix chemicals together.

Sometimes you'll have more than one type of weed to attack, which may require different types of chemicals. Never mix and apply multiple types of chemicals together in the same sprayer. Always spray separately and leave at least 7 days between applications when switching chemicals. 

Be prepared to spray more than once.

If you have had weeds in your lawn for a while or if you have a significant infestation, you'll most likely have a significant amount of weed seeds that won't take a lot of convincing to germinate once the current generation has been poisoned.  This can potentially mean spraying for extended periods to officially control the population.  Then there are the tough weeds that will need more than one spray to knock them off. Vigilance is the key here – Keep spraying as required. Some weeds, such as creeping oxalis will need to be sprayed every 2-3 weeks for an entire season to achieve control. Be patient. Some weeds die quickly, and others take a while. In some instances, weeds can carry on as normal for up to two weeks after spraying before they start to die.

While all of this sounds like a lot to take in, it's well worth spending some time doing your homework before you start. In this way, you'll have much better results, you'll be safer in your approach and you'll avoid unintended damage to lawns and gardens. 

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