Environmental influences on common waterhemp germination and tolerance to salinity and herbicides

AbstractThis study investigated the potential of common waterhemp [Amaranthus tuberculatus (Moq.) Sauer] invading the semiarid, salinity‐prone areas of the Central Valley (CV) of California, and its response to commonly used herbicides. Despite its status as one of the worst weeds in the US agriculture, common waterhemp is not very prevalent in California. Limited information exists on its germination ecology and potential to invade the CV, or its response to herbicides. Seeds were collected from a local common waterhemp population, and germination was tested under a range of water potential (0 to −4.17 MPa), salinity (0–25 dS m−1), and pH (5–9) levels. Plant tolerance to salinity at different electrical conductivity (EC) levels (0–20 EC) and mortality under applications of label rates of postemergence herbicides (glyphosate, glufosinate, rimsulfuron, or caprylic + capric acid) at the 4‐ to 6‐leaf or 8‐ to 10‐leaf stage were evaluated. Results showed that the seeds were moderately tolerant to drought and salinity as 50% and 55% of them germinated at −0.5 MPa and 10 EC, respectively. Germination was greater in neutral to alkaline than in acidic conditions. Plants were not very tolerant to salinity as 96% of them died at 10 EC. Most of the plants were controlled by herbicide applications at the 4‐ to 6‐leaf stage, but escapes occurred at the later stage. Therefore, the local population has the potential to germinate and establish in the CV but can be controlled by tested herbicides when applied at early stages.