By Donna Dolinar, Wyandotte County Extension Master Gardener since 2006
You are looking at your lawn and want to see lush turf, but what you do see is a crop of weeds. You have decided to spray a chemical weed killer (like 2,4D). Now you have some questions, like: When can I mow after spraying? Or Should I cut down the weeds first? Here is some information to consider.
The way a weed killer works is that you spray the portion that you can see, the leaves and sometimes the flower, and then the leaves absorb the substance and send it down to the roots. You want that weed killer to soak down to the root so that the plant will be destroyed. Otherwise, it will simply re-grow its leaves and propagate itself into more annoying weeds.
How Long Before I Can Mow?
The short answer is to wait as long as possible. You want to give the leaves time to not only suck up the chemical, but to transport it down to the root system so the weed gets good an sick. A rule of thumb is to give it 24 hours.
Realizing that you may not always have a day’s grace for mowing, the second choice is to follow the manufacturer’s information. Read the label. It will tell you the minimum amount of time between the application and rain and that would also apply to mowing.
How to Spray
Attack the weeds with your sprayer only until they are wet but not to the point of runoff.
Hose-end sprayers are discouraged. These create mists and air movement can cause the mist to drift quite a distance. The herbicide doesn’t distinguish between broadleaf plants and many flowers can be harmed by wayward spraying.
There are three kinds of lawns:
- Weed free – If you had that type of yard, you wouldn’t be reading this now.
- A few weeds – This is where you have the occasional unwanted plant but generally it is a nice bed of grass.
- Heavily weeded – This is when there are three or more weeds per square foot and usually covers a great deal of the yard.
For the landscape that has a few weeds here and there, simple spot spraying will do the trick. You can use a hand squeeze-trigger bottle for this purpose. If you don’t have a lot of weeds, but you do have a fair sized lawn, consider using a pump pressure sprayer. In either event, just attack the weed and not the whole yard. Hand sprayers give you significantly more control and that means you save product and, therefore, save money.
If the lawn is covered with weeds, use a broadcast or drop spreader with a granular product.
If you mow first, you don’t have as much weed surface to coat, plus those pesky weeds are a lot easier to spot when they are in full bloom. The preferred method is to spray weeds a day before, or at least a few hours before, mowing. That way you have the maximum amount of leaf area to cover with your chemical application.
Here is something not everyone realizes. If you have sprayed the plant but then walk over it (or let your pets romp, or children play, or drag an electric cord) and the weed is still moist from the herbicide, you are simply removing some of that substance.
It is a good idea to add a substance called “spreader sticker” to the sprayer. Many weeds have a waxy coating and just using a weed killer alone may not stick. There are a number of companies that make spreader stickers. You really only need a little bit in your sprayer and it is worth the price and effort. If you are using a granular product, find the right spreader sticker to go along with this method.
Before using any chemicals, read the label. Even if you are sure you remember all the details, read the label. Some of these substances can be harmful to humans and pets, and it is always better to err on the side of caution. If you have questions, most labels have website information or a phone number (frequently toll free). Don’t take chances.