Laboratory and greenhouse studies were conducted to determine the effect of temperature, soil moisture, light, planting depth, and rhizome water content on shoot emergence and vegetative growth of alligatorweed. Optimum shoot emergence and growth occurred at constant 30 C, and no shoot emergence was found below constant 5 C. A maximum shoot emergence of 93% occurred at constant soil moisture of 30% with temperatures of 10 to 35 C. Shoot emergence and growth decreased as rhizome water content decreased, and shoot emergence did not occur below a rhizome water content of 20%. Shoot emergence and growth decreased with burial depth; shoot emergence was above 90% when rhizomes were buried 0.5 to 1.0 cm deep compared to 16% when they were buried 18 cm deep. Alligatorweed shoot emergence and vegetative growth were not significantly affected by light. In the fields, shoot emergence began in late March and culminated in May and June. These data help explain why this species is most commonly found in crop fields, orchards, roadsides, rivers, lakes, ponds, and irrigation canals. This information may aid in the development of more effective management measures, such as bringing alligatorweed rhizomes to the surface or below 20 cm deep to restrain its emergence and growth at winter or summer plowing.

Nomenclature: Alligatorweed, Alternanthera philoxcroides (Mart.) Griseb ALRPH.