Lespedeza, often mistaken for clover, is a persistent and resilient weed that quickly takes over lawns, pastures, and natural areas, thriving even in poor soil conditions. Effectively controlling this weed requires understanding its life cycle and using a multi-faceted approach combining cultural practices with targeted chemical treatments. The goal is to kill existing plants and prevent the next generation from taking hold.
Identifying the Lespedeza Threat
Lespedeza is classified into two types requiring different management strategies: Annual Lespedeza and Sericea Lespedeza. Annual Lespedeza (including Common Lespedeza and Korean Clover) is a warm-season annual typically found in turfgrass. It is low-growing with a shallow taproot system. This type germinates in late spring and early summer, matures quickly, and produces seeds before dying with the first frost.
Sericea Lespedeza is a perennial species that presents a more aggressive challenge. It is often found in pastures and fields, growing as an erect, bushy plant that can reach heights of three to five feet. Both types are legumes, meaning they fix atmospheric nitrogen, allowing them to flourish in low-nitrogen soil where turfgrass struggles. The extremely hard seed coating allows seeds to remain viable in the soil for decades, creating a persistent seed bank that guarantees re-infestation.
Cultural and Mechanical Removal Methods
Mechanical control is a viable option for small, isolated infestations before the plants mature and set seed. Hand-pulling is most effective when the soil is moist, allowing for the complete removal of the shallow taproot. Complete removal is necessary to prevent regrowth, as the plant may regenerate if the taproot breaks off, especially the perennial Sericea type.
Adjusting turf management practices significantly reduces Lespedeza establishment by creating an environment where the weed cannot compete. Raising the mower blade height to three inches or more encourages a dense, tall turf canopy that shades the soil surface. This shading inhibits the germination and growth of new Lespedeza seedlings, which require sunlight to establish.
The weed thrives in thin, compacted turf, so alleviating soil compaction is an important cultural practice. Core aeration reduces soil density, allowing for better water and nutrient penetration and encouraging deeper turfgrass root development.
Aeration should be timed to allow the desired turfgrass to recover quickly, typically in the early fall for cool-season grasses. This timing prevents the voids created by aeration from being colonized by Lespedeza.
Choosing the Right Herbicide and Application Timing
Chemical control of Lespedeza requires a dual strategy involving both pre-emergent and post-emergent herbicides. Pre-emergent control prevents the germination of the massive seed bank remaining in the soil. These products must be applied in early spring, typically when soil temperatures reach the low to mid-50s degrees Fahrenheit, before the annual Lespedeza seeds begin to sprout.
Common pre-emergent ingredients effective against Lespedeza include prodiamine and dithiopyr. Applying a product with one of these active ingredients creates a chemical barrier in the soil, stopping emerging seedlings. Split applications, where a second, smaller application is made six to eight weeks after the first, can extend residual control into the summer months when germination peaks.
For existing plants, post-emergent herbicides are necessary. Timing is crucial for success, as Annual Lespedeza is most vulnerable when young and actively growing in the late spring or early summer, before its stems become woody.
A common and effective option for broadleaf weeds in turf is a three-way herbicide mix, which typically combines 2,4-D, dicamba, and mecoprop (MCPP). The dicamba and MCPP components are generally more effective against Lespedeza than 2,4-D alone.
Specialty chemicals provide stronger control, particularly for the resilient Sericea Lespedeza or when the annual weed has matured. Products containing metsulfuron, often combined with dicamba or sulfentrazone, offer good control in warm-season grasses.
For Sericea Lespedeza in pastures and non-turf areas, herbicides containing triclopyr or a combination of triclopyr and fluroxypyr are highly effective. These specialized treatments should be applied when the Sericea is actively growing, ideally when it reaches at least eight inches tall. Application during the early bloom stage also ensures maximum absorption.
Long-Term Turf Management for Prevention
Preventing the return of Lespedeza hinges on maintaining a dense, healthy stand of turfgrass that out-competes the weed. Lespedeza thrives in soils with low nitrogen and low pH (acidic conditions). Conducting a soil test is the first step to determine the specific needs of the soil, especially the pH level.
If the soil test indicates a low pH, applying lime (calcium carbonate) will raise the pH to a range more favorable for turfgrass, typically between 6.0 and 7.0. This adjustment makes the environment less hospitable for Lespedeza. A consistent nitrogen fertilization program is also necessary to give the desired turfgrass a competitive advantage.
The applied nitrogen helps the turfgrass grow quickly and densely, creating the shading effect Lespedeza cannot tolerate. Overseeding thin areas of the lawn with a desirable grass species further increases turf density, closing gaps where Lespedeza seedlings might establish. Deep and infrequent irrigation practices are also beneficial, encouraging the turfgrass to develop a deep, robust root system better able to withstand drought stress than the shallow-rooted Lespedeza.