According to Holm (1969 and 1977), Johnson grass ranks among the first 10 weeds worldwide due to the size of the damage. Johnson grass has a great ability to adapt and spread. This species produces thousands of viable seeds (Scopel et al., 1988), it is adaptable (Clements and DiTommaso, 2012), it does not rely on insects for pollination and it is spread by humans unknowingly (Christoffoleti et al., 2007; Ghersa et al., 1993). Through natural dispersal pathways (Holm et al., 1977; McWhorter, 1989; Parsons and Cuthbertson, 2001), it accumulates a large reserve of seeds in the soil in the long term (Parsons and Cuthbertson, 2001) and it is resistant to some herbicides (Heap, 2015). We can say that the extensive rhizome system and the prolific seed production make Johnson grass an extremely competitive and invasive plant (Holm et al., 1977). In agricultural ecosystems, it diminishes the productivity (McWhorter, 1989; Mitskas et al, 2003), increases the production costs (Keeley and Thullen, 1981; McWhorter and Anderson, 1981) and is toxic for animals under certain circumstances (Burrows and Tyrl, 2013). Although the past 20 years have witnessed continuous improvement of the methods of control of species Sorghum halepense, researchers are always looking for effective control strategies (Andújar et al, 2013a, Johnson and Norsworthy, 2014), including for the populations which are resistant at herbicides (Johnson et al., 2014). In 2015, an American study on the risk associated with the presence of species Sorghum halepense (https://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/downloads/wra/sorghum-halepense.pdf) revealed that, out of approximately 300 species under evaluation, Johnson grass obtained the highest risk score in terms of its potential to adapt and spread. Regarding the spreading of this species, at world level and in Romania, it has been observed that it is in continuous expansion, progressing even in colder areas. This leads us to believe that climate change will aid its spread (Follak and Essl, 2013). The competitive capacity of this species might come from an accelerated transfer of photosynthetic substances from the shoot to the rhizome. In addition to its competitive capacity, Johnson grass produces allelopathic substances. Crop losses due to weeds vary between 10 and 80% in the case of wheat, between 30 and 90% in corn and between 40 and 84% in soy beans (Sarpe, 1981, 1984 and 1987).

reduction, population, Sorghum halepense, herbicide, cyclohexanediones

field crops and pastures

Presentation: poster