By Tim Barnes, Owner of the Landscape Shoppe

When people hear the word herbicide, some stay away due to fear that media has created by stigmatizing anything to do with chemicals. Actually, without the use of herbicide in crop production, there is no way to feed our population – especially with labor and water shortages that many areas of the country are experiencing. With regard to herbicide and its value, the landscape industry is no different.

Using the right herbicide in the right application will save you major time on labor. And, understanding how to apply the proper chemicals in your landscape, may just free up a few more summer weekends! We basically have two types of applications that can be used, both commercially and residentially: Post-Emergent and Pre-emergent.

Non-Selective, Post-Emergent:

  • Post-emergent refers to after the weed plant has germinated and is in growth stage. Non-selective means that it will kill everything it comes in contact with. Typically, the most popular, safe and effective product is Roundup Herbicide. The chemical name for Roundup is Glysophate. When you purchase a non-selective weed killer no matter what the catchy name on the front of the bottle is, the main active ingredient will be Glysophate. Always look at the label to see exactly what the percentage of Glysophate is in the container. In fully-concentrated Roundup, Glysophate will be about 40% active ingredient, while the remainder is an inert ingredient to make up volume and dilute the Glysophate. Some Roundup variants also come with a “contact sticker” – a type of glue that helps the chemical adhere to the plant, even with moisture present. Remember to always read the label and check for the amount of actual glyphosate in the product. The higher the concentrate, the higher the dilution rate. Therefore, you will get more product per-bottle based on the amount of active ingredient that can be diluted with water. 

Selective, Post-Emergent:

  • Selective means that it differentiates between the weed to be eliminated, and the plant or grass to be kept. Dandelions, Chickweed, Knots edge, Crab grass, there are many. Depending on what weeds you wish to eliminate, whether that be in lawns, flower beds, or agriculture pertaining to a crop, apply selective, post-emergent herbicide. Sprayed over the top of grass, or other plants which are co-mingled with the undesired weed plant. For landscaping purposes, a common selective, post-emergent herbicide will have a combination, or concentrate, of the following: 2-4D known as dichlorophenoxyacetic acid, and dicamba – which is a variant of 2-4D. Spraying this product over Northwest cool-season grasses, will eliminate most weeds in lawns. Again, read the label. This will tell you the concentrate that you’re purchasing, how much to dilute that concentrate, and exactly what weeds it will eliminate.

Another selective, post-emergent commonly used is Crossbow. Crossbow is mainly used to kill Blackberries. Spray unwanted blackberries in the fall about the 1st of September. At that time, the plants are translocating the sugar’s produced from the fruits and leaves down to the roots for winter storage. When sprayed, the chemical will be translocated to the roots and a very good kill will take place if sprayed at this time of year. Crossbow has a high concentration rate, and can accumulate in your soil, moving downward to plant roots if used too heavily, or annually. For this reason, I caution against the use of Crossbow for other applications.

Pre-Emergent, Selective Herbicide:

  • A Pre-emergent herbicide is effective before a seed germinates, typically applied over soil in late winter. When the seed germinates in the spring, a vapor barrier is formed that kills the seed before it has a chance to root. Pre-emergents are selective as they will have different uses based on the chemicals within the blend. The most common for the Willamette Valley are Casaron and Preen. The main ingredient in Casaron, is Dichlobenil – which, even in very small amounts is a potent chemical. Preen’s active ingredient is trifluralin, it is less concentrated than Casaron, and is safer to use around lawns and some plants. Again, the most important process is to read the label of each product you are purchasing, and understand the plants and grasses that you are applying it to. 

Application, and Tips:

Most all post-emergents are in the liquid form, so they must be applied with a sprayer. Pre-emergents can be purchased and applied in both granular and liquid forms. The most commonly used is granular, because of its ease of application. Casaron has a patented spreader that will spray the chemical properly, without over applying. 

In attempting to treat some very difficult-to-get-to weeds, such as weeds growing amongst ground cover (wild Horse Tail Rush, for example), it is likely this may accidently subject the ground cover to over-spray. In that case, using a sponge or towel, fill a container with a diluted chemical mix. Then, wearing gloves, eye protection, and other proper PPE, apply the chemical solution to the unwanted weed. This method also works well on Blackberries and in grasses that are infested with speedwell or chickweed.

When using a backpack sprayer be sure not to over-apply, by avoiding multiple treatments to the same area. If you properly dilute the chemical, you only need to cover the ground once. For example, when selectively spraying post-emergent over cool season grasses to eliminate weeds, it is not necessary to spray multiple times. Doing so may severely risk stressing, and possibly killing the lawn that your trying to treat. A one time contact of the weeds within the grass will be sufficient.

A reminder to read the label of your chosen herbicide before use, and know exactly what plants and grasses you are treating. There is a lot of good information online regarding this subject, so always do your research.

I hope this helps in deciding if herbicide is right for your landscape application. If you have any questions regarding this blog, you can email me at