By Matthew L. Pfeifer
Wabaunsee County Extension Agriculture Agent
The competitiveness of sericea lespedeza is what makes it such a problem in Wabaunsee County.
Established sericea lespedeza plants will reduce or eliminate competing vegetation. It is relatively slow to establish, having a rather weak, vulnerable seedling stage. At the same time, it is opportunistic, and will establish itself in full sun or partial shade. Sericea lespedeza tolerates shade quite well, establishing in dense shade where direct sunlight does not reach during the day.
Germination and seedling growth are regulated by day length and temperature. Growth increases as day length exceeds 11 hours, with maximum seedling growth at 13 to 15 hours of day length. Optimum temperatures for germination and growth range from 68 to 86 degrees Fahrenheit.
During establishment, sericea lespedeza uses most of its energy to produce a root system. It has a deep, woody taproot, producing numerous branches that spread laterally and downward to a depth of three to four feet. Finer more fibrous roots also are produced. This extensive root system helps make sericea lespedeza competitive and somewhat drought resistant.
Sericea lespedeza has been found growing in ditches or fence rows without invading adjacent well-managed range and pasture, with good plant cover. Sericea lespedeza appears to establish best where competing vegetation is very short and light is allowed to reach the germinating seed and seedlings. Many legumes need good exposure to sunlight during the seedling stage, which is the situation found in a burned pasture. Fire is assumed to enhance establishment, possibly due to more sunlight available to the seed and seedlings. Seedlings will germinate and survive at low population levels where ground cover and other plant competition is quite dense, such as fence rows, brushy and grassy areas and where fire and grazing have been excluded for years.
When sericea lespedeza becomes established, it restricts the amount of light reaching other plants. Its tall, upright growth with multiple branches and dense foliage provides heavy shading. Cool-season grasses, such as Kentucky bluegrass, are better able to survive shading caused by dense stands of sericea lespedeza. Warm-season grasses, such as big bluestem, may survive some shading, but will be weak and produce little forage unless the shading is removed.
The photosynthetic rate of sericea lespedeza is only half that of alfalfa. It requires more water to produce foliage than other warm-season plants, creating a "drought" for competing vegetation. The plant produces allelopathic chemicals, which inhibit seed germination and growth of some plants. These chemicals are released from the roots and leached from other plant residues, chiefly leaves.
Sericea lespedeza is a legume, but has a low nitrogen fixation rate and has little effect on the status of soil nitrogen. It has been shown to increase the nitrogen content of associated grass, but what nitrogen is supplied is offset by the allelopathic substances produced. Grass shoots exposed to allelopathic substances have lower nitrogen content, resulting in reduced forage quality. Nitrogen fertilizer is required to maintain production of introduced forage grasses grown in mixtures with sericea lespedeza.
Sericea lespedeza is a prolific seed producer. Individual stems may produce in excess of 1,000 seeds, with 300 to 600 pounds of seed produced per acre. There are about 350,000 seeds per pound. Most sericea lespedeza seed is hard, with normal germination rates of only 10 to 20%. The seeds are nearly impervious to water, so they must be scarified to enhance germination. These seeds may lay dormant for years. So, even after this weed is thought to be controlled, the areas must be watched for re-emergence.