Managing Lawn Weeds in Spring

With spring coming soon, we will begin to get outdoors to improve our lawns, and just be outside. Make sure you know what weed you are dealing with in your landscape and know the best way to control it. There are times for controlling weeds, it may not be the best in spring for all. Spraying at the wrong time is a waste of money and can be harmful to our environment.

Crabgrass

Crabgrass is one of the most problematic weeds in lawns. It is a summer annual weed. Summer annuals germinate in the spring, grow and produce seed throughout the summer and die with the first frost in the fall. Crabgrass germinates when the soil temperatures average 55-60 degrees Fahrenheit. So, crabgrass preventer should be applied when the soils reach that temperature. Typical preemergence herbicides include dithiopyr, prodiamine, or pendimethalin as the active ingredient. A second application should be made in late May to June for season-long control.

If you miss the window for preemergence products, you still have options. There are some great post-emergence products. Dithiopyr and mesotrione have pre- and postemergence activity on crabgrass. Quinclorac is a great postemergence herbicide that is often found in the product Drive. So any of these can be used if you miss the spring window for control.

Annual Broadleaf Weeds

Henbit is a winter annual. A winter annual is a plant that germinates in the fall and grows a bit before basically becoming dormant for the winter months. Very early in the spring, henbit will start to grow again, produce flowers and seed for the next year then it will die when the temperatures warm up. This is different from a summer annual which germinates in the spring and goes through its lifecycle through the summer months and dies with our fall frosts.

The problem with henbit is that by the time we see it, or rather see the purple flowers, it is too late to treat for the year. Once the flowers begin to show up, it is already producing seed for next year, so killing blooming henbit is unnecessary because it will die naturally and the chemicals won’t reduce production for next year. However, pulling the plant would be a fine management practice after blooming has begun. It can be sprayed with a 2,4-D product very early in the spring once it has greened up but before it blooms. If you know where it is you can spray it before it blooms. Otherwise, wait until this fall to spray those areas with a preemergence herbicide before it germinates in the fall.

Perennial Weeds

We have a lot of perennial weeds in our lawn as well. Plants like dandelions, creeping Charlie, and clover are perennial broadleaf weeds. Perennial weeds are best controlled in the fall once the weeds have begun their preparations for winter. In the fall, these perennial weeds will move sugars that they use for energy from the above ground portions of the plant down into the roots to store them for next spring. If they are sprayed during this phase of their lifecycle, they are more likely to take that herbicide down into the roots to be more effective than if done in the spring. Spraying these weeds in the spring will knock them down, but likely not kill them outright.

Nimblewill is a perennial grassy weed. It is controlled through one of two methods. You can spray it with a product containing mesotrione that won’t harm the surrounding grass. Or you can spray it with a glyphosate product, such as Roundup, then overseed the area. The glyphosate will only be effective if sprayed on the nimblewill when it greens up, and this is a warm season grass so it will be later in the summer. It is best to do this in August then you can overseed 2-3 weeks later.

*Reference to commercial products or trade names does not imply endorsement by Nebraska Extension or bias against those not mentioned.

Crabgrass

crabgrass, Joseph Berger, Bugwood
Crabgrass photo, courtesy of Joseph Berger, Bugwood.org

This time of the year is always full of activities to do outside. It is a great time to get outside in the comfortable weather. Lawncare is always at the top of our spring outdoor ‘to do’ list, and crabgrass is number one on the concerns.

Crabgrass Basics

Crabgrass is a summer annual grassy weed that takes advantage of thin areas in our lawns to become established. As a summer annual weed, crabgrass germinates in the spring and, if not controlled, new plants continue to germinate throughout the summer. Each plant grows for one summer, then dies with the first hard frost in the fall. New crabgrass that you see in your lawn each year is from seed that was set the previous year by the crabgrass growing before.

Crabgrass is a problem in our lawns. Each plant will compete with our desirable grass species. Once crabgrass gets into a lawn, it will compete with our grass for water, sunlight and growing space. Plants produce a large amount of seed that will germinate the following year, creating an ongoing problem on your lawn.

Prevention

Crabgrass is difficult to eradicate once it becomes established, so it is better to prevent this weed from becoming established in the first place. Crabgrass preemergent herbicides are used to inhibit the growth of young seedlings, destroying them before they can emerge from the soil. Which is why many people prefer to use a preemergent herbicide to control the crabgrass in their lawn.

Preemergent herbicides should be applied before crabgrass has started to germinate, which happens when soil temperature has reached 55-60 degrees F, measured at 4-inch soil depth, for at least four days. This is not based on a date range, because soil temperatures differ from year to year. It is based on the weather conditions for that year. We have reached that point now this year.

It is not beneficial to apply the preemergent too early in the year. Once applied products begin to degrade and breakdown. If your application is made too early, before crabgrass germination has started, you are wasting your product and monty because you will have a shortened period of control once crabgrass does start germination.

Plan on making two applications of preemergent to give season-long crabgrass control. Purchase enough product in spring for two applications; garden centers often run out of preemergent products by the end of spring so it could be hard to find later in summer. Each product has a slightly different length of residual action, so follow the product’s label directions on when the second application should be made.

Controlling Existing Plants

Post-emergent herbicides can be used to control crabgrass that has emerged in your lawn. Products containing Mesotrione, commonly found in the product called Tenacity, works as both a pre- and post- emergent herbicide on grasses and broadleaf weeds. It can also be used at seeding if you have a history of crabgrass problems and need to overseed.

The other commonly used post-emergent herbicide for controlling crabgrass would be products that contain Quinclorac, commonly found in the product called Drive.

If crabgrass does appear in your lawn, you can reduce future problems by keeping plants mowed short enough that they don’t produce seedheads. Then at least there won’t be additional seed in the soil to increase your problem next year.