LSU AgCenter Horticulturist
(10/23/20) Second to sod webworms, common lespedeza is winning the lawn headache contest right now. Over the past few weeks, LSU AgCenter offices across the state have been getting many questions about this weed in the lawn.
Common lespedeza is a warm-season annual weed with a low, mounding or clumping growth habit. It stands out in the lawn because of its dark green foliage compared with grass blades. Common lespedeza is identified by its dark green, small, rounded, trifoliate leaves, tiny purple flowers and woody stems. These woody stems can make this weed rather difficult to control.
It is actually a member of the pea family of flowering plants commonly known as bush clovers and is, botanically speaking, a legume. Although common lespedeza is considered a weed in the form we are lamenting over in our lawns today, a beautiful ornamental species commonly referred to as Thunberg’s lespedeza is just amazing.
Thunberg’s lespedeza is a deciduous shrub that grows gorgeous cascading and arching stems. The tiny and abundant flowers are major attractors of bees, butterflies and other pollinators. I love it, and its gorgeous cascading form makes it a unique feature in the landscape.
With the heat and dry weather of the summer leading up to fall, turfgrasses can suffer and decline if not properly cared for. When this happens, weeds take advantage, specifically in thinned or stressed areas of the lawn. Either excessive water or drought can cause stress in lawns that leads to an increase in weeds.
Lespedeza is what we refer to as an indicator weed because it tells us what is going on in the lawn. This weed thrives in soils that are dry, compacted and low in nitrogen. In that aspect, you can be thankful for the information the weed is telling you about your lawn so you can correct the problem. However, fall and winter are not the time to do this.
Lawns should be fertilized and aerified when the turfgrass is actively growing. Southern turfgrass begins its dormancy with cooler weather. Common lespedeza will go into winter dormancy as well and will no longer be a problem until spring when plants emerge from seeds again. If not taken care of, it can become established again by summer, and you are back where you started.
The best way to stay on top of this weed and reduce its abundance is to maintain a healthy, vigorous lawn. This can be done with proper cultural practices such as mowing and fertilizing.
In spring, improve soil quality by reducing compaction and increasing fertility. The best time to aerate and fertilize your lawn is when it is actively growing, starting in April into early fall by the end of September or early October.
To reduce compaction, aerify your lawn. Aerificaiton methods commonly used in home lawns are core removal with hollow tubes that remove a core of soil and grass and solid tine aerification that uses tines or spikes to poke holes in the turf. Core removal is the most effective method; however, it requires more cleanup.
The purpose of aerification is to reduce soil compaction and to improve oxygen movement to the root zone. You should aerify your lawn every one to three years depending on the soil type (clay requires more frequency because it is prone to compaction).
Next, ensure proper fertility in the lawn by applying the proper rates of nitrogen in spring. You may continue to fertilize every other month until grasses begin to go dormant in September if soil tests indicate a deficiency.
Avoid applying fertilizers in fall and winter when grasses go dormant or when you stop mowing. Following these recommended nitrogen rates per 1,000 square feet per year and mowing heights for each turfgrass species will help ensure proper growth and vigor.
— Bermuda grass: 2 to 3 pounds of nitrogen; mow at 1 to 2 inches.
— Centipede grass: 1/2 to 2 pounds of nitrogen; mow at 1 to 2 1/2 inches.
— St. Augustine grass: 1 to 3 pounds of nitrogen; mow at 2 1/2 to 3 inches.
— Zoysia: 1/2 to 2 pounds of nitrogen; mow at 1/2 to 2 inches.
As a second line of defense in spring, hand removal of tender weeds can be done on any breakthrough weeds. If the weeds do thrive despite aggressive cultural practices, you can use chemical control.
Post-emergent herbicides containing metsulfuron or a product that contains thiencarbazone, dicamba and iodosulfuron have been found to be the most effective herbicides on young, actively growing weeds according to LSU AgCenter researchers.
Second treatment applications may be necessary to obtain good control or complete removal of the weeds. Always follow the manufacturer’s label directions for proper application. An AgCenter publication on lespedeza control is available online at http://bit.ly/lespedezacontrol. In includes a suggested list of herbicides labeled for use in lawns for control of common lespedeza.
Don’t let this weed get the best of your lawn or the best of you each summer. Ensure your lawn is healthy and growing vigorously to prevent weeds. On the other hand, you could let the pollinators enjoy them.
Common lespedeza weed has oval-shaped leaves in a trifolate pattern. Photo by Heather Kirk-Ballard/LSU AgCenter
Common lespedeza grows in a mounding habit in thinned out areas of turf. Photo by Heather Kirk-Ballard/LSU AgCenter
Thunberg’s lespedeza has a fountain-like mound of arching stems full of gorgeous blooms. Photo by Heather Kirk-Ballard/LSU AgCenter
Thunberg’s lespedeza displays gorgeous pea-type flowers in the fall. Photo by Heather Kirk-Ballard/LSU AgCenter