Praxelis [Praxelis clematidea (Griseb.) R.M.King & H.Rob.] is an invasive species that infests many agricultural systems globally, such as orchards, rubber plantations, and other economic crops. The purpose of this research was to study seed morphology, germination factors, and allelopathy of aboveground parts of P. clematidea. P. clematidea seeds are small, light, and possess pappi that allow them to be dispersed easily by wind or animals. Among four P. clematidea populations collected from different provinces in Thailand, the size of P. clematidea seeds ranged from 2.6 to 3.2 mm in length, 0.6 to 0.7 mm in width, and were 0.4 mm in thickness. The weight of P. clematidea seeds ranged from 0.13 to 0.21 mg. P. clematidea had about 44 to 48 seeds per head. Seeds germinated over a temperature range of 20 to 30 °C while high (45 °C) and low (10 °C) temperatures reduced germination. Maximum germination occurred when seeds were planted on the soil surface. No seedlings germinated when seeds were planted at a depth more than 1 cm. P. clematidea extracts from aerial plant parts at concentrations of 25 and 50% inhibited seedling growth of hairy beggarticks (Bidens pilosa L.). Basic knowledge of the seed biology of P. clematidea and allelochemicals can help in understanding the invasiveness and in developing management strategies for this weed.

Meadowfoam seed meal (MSM), a by-product after oil extraction, has potential uses for crop growth enhancement or weed control. The herbicidal effect of MSM is the result of a secondary metabolite, glucosinolate glucolimnanthin (GLN). Field evaluations were conducted using concentrations of 3, 5, and 7% by weight and two forms (nonactivated and activated) of MSM applied as soil amendments. No injury was observed on lettuce transplanted 7 d after MSM incorporation in 2011. Activated MSM at 7% reduced weed emergence up to 71%. Lettuce leaf N content was at least 8.5-fold greater in MSM treatments compared to the untreated control. Greater soil nitrate levels correlated with greater weed biomass in MSM-amended plots. Isothiocyanate, a potent herbicidal compound, was detected in soil incorporated with 7% activated MSM. In 2012, 2.86 g m⁻² of activated MSM, applied as a split or single dose, was evaluated for weed control efficacy and crop injury response. The split MSM application provided weed control similar to that from the single MSM application. The split and single MSM applications inhibited spiny sowthistle emergence more than 95% compared to the untreated control. A single application of activated MSM as a PRE soil amendment suppressed weeds and increased lettuce yield.

Background: In Thailand, Echinochloa crus-galli (L.) P. Beauv. (barnyardgrass) is the most problematic weed in rice. Quinclorac was first commercialized in 1997 in Thailand and became the primary herbicide option for barnyardgrass control. The intensive use of quinclorac in rice fields increases the risk of the evolution of resistant barnyardgrass. Objective: This study was conducted to survey the occurrence of quinclorac-resistant barnyardgrass in Thailand, investigate the levels of quinclorac resistance, and evaluate alternative control measures for quinclorac-resistant barnyardgrass. Methods: [...] Background: In Thailand, Echinochloa crus-galli (L.) P. Beauv. (barnyardgrass) is the most problematic weed in rice. Quinclorac was first commercialized in 1997 in Thailand and became the primary herbicide option for barnyardgrass control. The intensive use of quinclorac in rice fields increases the risk of the evolution of resistant barnyardgrass. Objective: This study was conducted to survey the occurrence of quinclorac-resistant barnyardgrass in Thailand, investigate the levels of quinclorac resistance, and evaluate alternative control measures for quinclorac-resistant barnyardgrass. Methods: