Optimum Soil Moisture and Temperature for Khakiweed (Alternanthera pungens) Emergence.

The lack of control for khakiweed (Alternanthera pungens Kunth) after establishment is a major concern for golf course superintendents, recreation area managers, and homeowners. Khakiweed is a herbaceous creeping perennial that reproduces by seed and vegetatively. Curative approaches to controlling khakiweed have not provided adequate, long-term control (>90%). The objective of this research is to determine optimum soil moisture and temperature for khakiweed seed emergence to aid turfgrass managers in the timing of their pre-emergence herbicide applications. In 2010 and 2011 field and laboratory experiments were initiated in Las Cruces, NM, with various soil moistures and temperature treatments chosen from similar plants in literature. Initial emergence in the field was seen with daily average temperatures of 16 C and emergence ceased once average temperatures dropped below 16 C. Lab experiments were conducted in an incubator and emergence was first seen at 10 C. However, at 20 C emergence of khakiweed seed was no longer water dependent and emergence rates ranged from 42-50%, with no statistical difference between the rates. No emergence of khakiweed seed was observed at 50 C. With adequate soil moisture, turf managers should apply pre-emergence herbicides before soil temperatures reach 10-16 C. At 20 to 30 C, all moisture levels had khakiweed emergence. Due to the wide range of soil moisture, temperature, and the long duration of emergence in southern New Mexico, multiple pre-emergence herbicide applications will be necessary to sustain adequate control.