2,2-DPA resistance in Giant Parramatta Grass (Sporobolus fertilis)

Summary Sporobolus fertilis seeds suspected of being resistant to 2,2-DPA (sodium 2,2-dichloropropionate) were collected near Grafton, NSW, Australia. A seedling Petri-dish assay showed that the 2,2-DPA concentration required to reduce shoot length by 50% in the resistant biotype was about 500 g a.i. kg-1, five times greater than that for the sensitive biotype. Similarly, a pot-dose assessment in plants showed that the resistant population required 4 and 28 kg a.i. ha-1 for 50% reductions in shoot height and the proportion of live leaves per plant respectively, more than 2.5 and 14 times the recommended rate, whereas the sensitive plants were well controlled by the recommended rate. This shows that 2,2-DPA resistance has indeed developed in the field and will limit the use of 2,2-DPA for the control of S. fertilis in future.