Modelling strategies to prevent resistance in black-grass (Alopecurus myosuroides)

A single dominant mutation conferring resistance to aryloxyphenoxypropionat e (AOPP) and cyclohexanedione (CHD) herbicides was incorporated into a quan titative model for the population development of Alopecurus myosuroides. Th e model assumes an initial seedbank of 100 seed/m(2) and that each generati on a proportion 10(-6) of the seedbank mutates to resistance. The model pre dicts that with annual use of AOPP/CHD herbicides which kill 90% of suscept ible but no resistant plants, a threshold of 10 plants/m(2) surviving herbi cide ('field resistance') will develop: in 9-10 years if all tillage is by tine cultivation to 10 cm deep; after 28-30 years of continuous ploughing; in 12 years if tine cultivations are interspersed with ploughing once every four years. If AOPP/CHD herbicides are alternated with herbicides with dif ferent modes of action, the predicted outcomes depend on the annual kill ra te: with 95% kill (of susceptible plants by AOPP/CHDs and all plants by alt ernative herbicides) and tine cultivation, field resistance develops in 22 years; however with a 90% kill and tine cultivation, field resistance does not develop but there are more than 10 susceptible plants/m2 surviving herb icide within 10 years. The model predicts that resistance can be delayed in definitely if three herbicides, each with a different mode of action, are r otated and 95% kill is maintained by each.