Autumn-germinating seeds pose weed threat in winter cereals
Autumn-emerging plants produce about 23 times as much seed as spring-emerging ones. As a result, weed control should focus on autumn, rather than spring, treatments.
Although seed dormancy is short-lived, peak germination occurs in autumn-sown crops two to three weeks after the soil surface becomes thoroughly moist and most seed will then emerge by November.
It is vital that farmers are observant to ward off any potential issues according to the AHDB.
It believes this starts and finishes with thoroughly cleaned equipment which can be one of the most effective means of limiting the spread of Italian ryegrass seeds – across arable fields and farms.
It also advises farmers to consider varied crop rotation, as it said evidence suggests that using break crops or long-term leys, is proven to reduce Italian ryegrass populations.
Ploughing is also especially effective, as the seeds cannot germinate at depth.
One key aspect that AHDB also recommends is delayed autumn drilling. It believes that waiting until late October, where possible, can be advantageous.
The development board has highlighted that this approach exploits the lack of seed dormancy, while avoiding the use of herbicides is also, it states, one of the best resistance management strategies.
But the AHDB also acknowledges that this approach may be impractical, in many situations.
Fundamentally, the development board advocates that good resistance management should involve farmers rotating herbicides with different modes of action across seasons.
Research trials have confirmed that a variety of active ingredients and well-timed herbicide applications at the recommended rates have proven effective at reducing Italian ryegrass populations.
The AHDB believes that effective herbicide control in the autumn can be central to success, which in turn also helps to reduce secondary peak emergence in the spring.
The development board states that a herbicide programme that combines pre-emergence and post-emergence herbicides should be considered in a management plan, as well as applying glyphosate to fallows, break crops and as a pre-harvest treatment.
Early signs
Overall, the AHDB said it is crucially essential that growers monitor for early signs of poor control following herbicide applications.
It outlines that resistance tests are a valuable tool to ascertain if resistance is present or whether issues may derive from poor herbicide application practices.
However, it is also important to note, according to the development board, that different forms of resistance can occur across a range of locations and these must be considered when designing herbicide programmes.
The AHDB said farmers should be aware of a field’s weed population and herbicide resistance statuses and then tailor management for sustainable long-term control.
The board has stated that herbicide-resistant Italian ryegrass does not represent a challenge for Ireland’s tillage industry, but there is no room for complacency.
In the UK, approximately 500 Italian ryegrass-resistant sites have now been identified, with perennial ryegrass the first plant to show resistance to glyphosate.
In light of these developments, AHDB is urging Irish tillage farmers to be vigilant to any Italian ryegrass plants that they may be growing in their fields.
