Week of April 4, 2022
Kathleen Cue, Nebraska Extension Horticulture Educator in Dodge County
If crabgrass has been a problem in your lawn, now is the time to be watching soil temperatures. Why is soil temperature important? Because a well-timed application of pre-emergence herbicide limits crabgrass seedlings while ensuring the herbicide works to its longest advantage.
Here’s what we know about crabgrass. Seed germinates when soil temperatures reach a consistent 55° F and warmer. Given the right soil temperature and moisture, crabgrass seeds can germinate throughout the growing season. Crabgrass takes advantage of open spaces, so having a dense lawn is your first line of defense against crabgrass taking over a space.
Here’s what we know about pre-emergence herbicides. Like its name implies, a pre-emergence product targets seeds as they are germinating, but before they break the soil surface. A few products will also kill seedlings that have already emerged, but not all pre-emergence herbicides have this capability, so reading the product label is important. Also, applications do not extend control through the whole growing season. The efficacy, how long the product application remains effective, varies from one pre-emergence herbicide to another. Look to the label to find how long an application lasts and then mark the calendar so a second application can be made, ensuring a longer period of crabgrass control into the growing season.
Putting down a pre-emergence application too soon, before crabgrass seed germination takes place, means sun, wind, temperature variations, and rainfall begin to degrade the product, cutting down on the length of time the herbicide does its job. Even though lawn care companies start early with their pre-emergence herbicide applications to get all their clients’ lawns into the spring schedule, the companies address seedlings they’ve missed with a post-emergence application. Homeowners, however, can save themselves money and frustration by seeing to it the pre-emergence herbicide applications are timed correctly.
The easiest way to time pre-emergence herbicide applications for crabgrass control is to check the soil temperature at the IANR CropWatch webpage at Soil Temperature Update | CropWatch (unl.edu) . Once a consistent soil temperature (3-5 days running) of 45-50° F has been reached, it’s time to do the pre-emergence herbicide application. Soil temperature can also be monitored by inserting a thermometer into the soil, an automotive or cooking thermometer will do, to a depth of 4 inches.
A well-timed application of a pre-emergence herbicide limits crabgrass seedlings while ensuring the herbicide works to its longest advantage, saving time, money, and frustration.
Visit Tree, Plants and Insects for more horticulture information.