After one of the wettest seasons for some time – and the inherent difficulties in terms of timely applications – there are many paddocks in the western district and Gippsland with poor levels of weed control.
This includes grass weeds such as ryegrass, wild oats and brome, and broadleaved weeds like wild radish.
GRDC-funded roadside surveys carried out by Southern Farming Systems (SFS) in conjunction with the University of Adelaide during the past five years revealed resistance levels average 80-85 per cent for Group B and Group A herbicides in the western district’s ryegrass.
As we continually use the same groups of herbicides to control problem weeds, so does the level of selection pressure which selects for the weeds resistant to the herbicides being used.
At this time of the season these problem weeds become obvious in the paddocks, standing up above the rest of the crop. Now is an ideal time to collect seeds from them – and prior to harvest if possible. Spotting these problem areas is made easier from the header seat, which provides a great viewing point from above.
A test for resistance is the only way to be sure a weed is resistant to one or more herbicides. Seed tests are slow and require 10-12 weeks to complete. Therefore, collection and submission of samples are required by mid-January to ensure results are available for preseason planning.
Sampling processes depend on the resistance situation of the paddock. Take care to spread sampling across a large number of plants and collect a similar number of seeds from each plant sampled.
For testing, more seed is better than less. When sending seeds, it's important they are contained in paper envelopes or bags and not plastic bags, particularly if the seeds are not totally dry, as they can rot. Double bag them, that is, place seeds in a paper bag and then insert this bag inside the paper envelope.
It is less expensive to spend a few hundred dollars on a resistance test than thousands on specific herbicides that are not effective.
