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Temperature effects glyphosate resistance. Glyphosate is more effective when applied at cooler temperatures. Air temperature is important in glyphosate application. This study determined the effect of glyphosate on a glyphosate‐resistant (GR) and glyphosate‐susceptible (GS) biotype of junglerice (Echinochloa colona L.). Potted plants at the 4‐ to 5‐leaf stage were acclimatized for 72 h in growth chambers programmed for day/night temperatures of 15/10, 25/20, and 35/30°C. On the fourth day, three plants of each biotype were treated with glyphosate at 840 g ae ha−1 and immediately placed back in the respective growth chambers and grown for seven additional days. Three non‐treated plants of each biotype were used as controls for each temperature regime. On the eighth day after glyphosate treatment, the plants were moved to a greenhouse set at 22°C, grown for 21 d, and aboveground dry weights recorded after evaluating phytotoxicity. None of the treated GS plants survived at any of the temperatures while all the non‐treated plants grew well at all temperatures. All treated and non‐treated GR plants showed no phytotoxicity in the 25/20 and 35/30°C temperature regimes. However, all the treated GR plants subjected to 15/10°C died. The aboveground biomass of the non‐treated GR plants was reduced under cooler temperatures but was unaffected in the GS plants. Therefore, this study showed that GR junglerice was susceptible to glyphosate when grown under 15/10°C suggesting that the prevalence of GR plants in the fields could be reduced if glyphosate applications were made in spring when temperatures were at or below 15°C when the plants were just emerging or had developed less than six leaves.

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Hairy fleabane (Erigeron bonariensis L. Cronq.) is an invasive weed in lowdisturbance annual, perennial, and noncrop systems in the San Joaquin Valley (SJV), California. It is often observed emerging year-round in diverse environmental conditions in the SJV. However, very little information is available on the reasons for this. The study aimed to assess the effect of temperature, water potential, salinity, pH level, and dormancy periods on hairy fleabane's germination. Tests were conducted at different day/night temperatures (5:0, 10:5, 15:10, 20:15, 25:20, and 30:25 ˚C), water potential (0 to -5.56 MPa), salinity (0-25 dS m -1 ), and pH (5-9). Germination tests were also performed on seeds the day they were collected from mature plants, and 7, 14, and 21 d later. Tests were conducted in growth chambers set to 20 ˚C or under ambient laboratory conditions at 22 ˚C. About 1% of the seeds germinated at 5 ˚C but maximum germination occurred at 25:20 ˚C. About 9% of the seeds germinated at -0.51 MPa and the estimated value for 50% germination reduction was -0.2 MPa. Seed germination had high tolerance to salinity, as 42% of the seeds germinated at 15 dS m -1 . Germination did not differ across pH levels. About 50% of the seeds germinated the day they were collected, indicating that this species had a very short seed dormancy requirement. These findings could explain why hairy fleabane is observed emerging year-round in the SJV, particularly in irrigated cropping systems. INTRODUCTIONHairy fleabane (Erigeron bonariensis L. Cronq.) is considered to be a native plant of the more temperate parts of South America (Michael, 1977). In the United States, it is now a common annual weed in cropped and noncropped areas of California (Shrestha et al., 2016), and other west coast and southern states (USDA-NRCS, 2021). Thébaud and Abbott (1995) considered this species as a summer annual weed, and it is classified as a summer annual weed in California

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