2023 spring clean for grass weeds

Agronomy Issues
1024 x 576 Large overwintered wild oats in this seasons crops.jpg

Growers and agronomists should be assessing crops now for the size of overwintered grass weeds, to prioritise fields for Axial Pro application as soon as conditions allow.

Field assessments have shown some larger overwintered wild oats and ryegrass this season that will have a significant implication for Axial Pro spring control strategies, advises Syngenta Technical Manager, Pete Hawkins.

Pete Hawkins

“Weed size and populations are very variable this season. With many crops drilled early in an open autumn and the variability of success from pre-emergence programmes - which depended largely on rainfall and soil moisture - some fields now contain relatively large weeds.”

 

Pete’s Top Tips for this season's spring grass weed control

  • Prioritise fields with the biggest weeds
  • Apply Axial Pro as soon as conditions permit (from 1st February)
  • Don’t delay for spring weed emergence
  • Adjust application rates to target weed and size
  • Tank-mix with a broad-leaved weed herbicide for one-spray solution

 

New NIAB research with Syngenta has shown that it’s these larger, overwintered grass weeds  (below) that have the greatest effect on yield loss and produce higher numbers of viable seeds to perpetuate problems in the future.   

1024 x 576 overwintered wild oat 2.jpg

The research revealed October germinated winter wild oats to grow an average four times bigger and become more competitive, compared to early spring germinating weeds.

“The cold weather in December and January may have checked growth, but most weeds will have recovered strongly,” he warned.

“Large weeds are also often associated with bigger crops, which can make targeting with herbicides more difficult.”

1024 x 576 ryegrass overwintered.jpg

Pete advocates treatment of wild oats and ryegrass (above) with Axial Pro as soon as weather conditions enable consistent plant growth, from the 1st February. Good growth of target weeds means the herbicide is more  effectively translocated down into the root, to achieve a complete kill.

“Take advantage of any good application opportunity to target grass weeds early this spring.” 

“While there may be a temptation to delay treatment, to allow later germinating grass weeds to come up, the research has shown these later emerging weeds pose far less threat to the crop and produce a much lower seed return at maturity.”

1024 x 576 Overwintered ryegrass in winter barley.jpg

“Holding off grass weed control will result in more competition on crop yields and could prove more difficult to control larger weeds, including ryegrass (above) – requiring higher Axial Pro rates and a greater challenge for application.”

With overwintered wild oats, for example, up to growth stage 29, an Axial Pro rate of 0.6 l/ha is advised  increasing up to the maximum 0.82 l/ha once the oats are past growth stage 30. If  growing conditions are sub-optimal consider delaying application or use the higher dose rate.

For larger weeds, up to growth stage 39, and for all ryegrass treatments, the higher rate of 0.82 l/ha would be the default, he added.

Pete pointed out that tank mixing Axial Pro with a compatible broad-leaved weed herbicide can achieve a complete spring clean-up in a single spray, to reduce time and cost.

But where it is being used in a herbicide sequence that includes SU/ALS or hormone broad-leaved weed treatments, applying the Axial Pro first ensures the grass weeds can be taken out at the optimum time, shortly followed by broad-leaved weeds seven days later. Otherwise, a 21-day interval is required after an ALS/hormone herbicide has been used before the Axial Pro can be applied.

Early removal of grass weeds is paramount to protect yield, and to minimise seed return in a sustainable weed control strategy.