Short rotations cause herbicide resistance! This is because of the inherent lack of diversity.
Weed populations quickly respond to routine management practices – those that survive will set seed and their progeny have an advantage when the same control tactic is used again soon after.
Principle #1 Diverse herbicide choices, diverse cultural practices
Following a longer crop rotation, and including a pasture phase if possible, means having more tools in the toolbox—better herbicide rotation, a range of seed set control options, varied planting times, competitive crop species or varieties and the ability to implement a variety of harvest weed seed control options.
If you can’t see your way clear to lengthen your crop rotation, look for ways to increase diversity within the crops you grow. Changing varieties may allow a different sowing time and in herbicide tolerant crops such as canola, you can rotate between the RR and TT hybrids. In a tight rotation harvest weed seed control and maximum crop competition are even more important.
Principle #2 Use double breaks, fallow and pasture phases to drive the weed seedbank down over consecutive years
Rotating to a double (or triple) break crop is a great way of smashing the weed seed bank, setting the paddock up for a long crop phase.
Examples of double break combinations are hay/canola, pulse/canola and fallow/canola and single breaks are still often used in the rotation. Some growers also include two crops of the same type (e.g. two cereals) in succession and rotate chemistry or change planting date.
If you can include a pasture, it is important that you always go into the crop phase with low weed numbers and also go into the pasture phase with low numbers. Sowing a pasture should not be seen as a re-set option after a weed blow out.
Take a planned approach right across the pasture phase and use a number of tactics known to be highly effective at preventing seed set. Several of the tactics available for use in a pasture phase can provide over 90 per cent control of the target weeds. The plan needs to outline how the pasture phase will fit into the crop rotation and what tactics will be used seasonally and rotationally to maximise the effect on weed numbers.
Including a pasture phase does not always mean gearing up to run livestock. The pasture could be grown for hay or silage or even as a fallow cover crop.