Farmers must be bold and take a “zero tolerance” approach to spring-emerging black-grass and populations that survived autumn control, urges Hutchinsons agronomist and Norfolk farmer Alex Wilcox.
Although autumn control was generally very effective given favourable weather and soil conditions well into November, he warns that high dormancy means there is a continued risk of fresh black-grass emergence into the spring.
Early treatment of small susceptible weeds is crucial, but growers must also ensure black-grass is actively growing to maximise efficacy of post-emergence chemistry, he says. This may require patience, especially when coming out of a cold spell.
In winter wheat, Mr Wilcox favours using a full rate of an iodosulfuron-methyl-sodium + mesosulfuron-methyl-based product applied as soon as conditions are suitable. He also recommends including a water conditioning agent such as X-Change to enhance control.
“Even where resistance to this chemistry is present in field populations, there will still be some black-grass control and there is added value from control of wild oats and a range of broad-leaved weeds.”
Fields should be walked over winter to identify and map problem areas of black-grass ready for treatment, he advises. “There’s got to be a zero tolerance approach towards any patches of black-grass.”
He acknowledges there is limited ability to control black-grass in oilseed rape into the spring, but insists it must be a cleaning crop to avoid stoking up future problems, which again means a no-tolerance approach.
“If you haven’t achieved good control from propyzamide-based products then be brave and mark these areas out, spray them off and re-drill with a hybrid spring oilseed rape.”
For those putting problem black-grass areas into spring cropping, Mr Wilcox says minimising soil disturbance at drilling is key to avoiding a flush of black-grass within the spring crop. Direct drilling can therefore produce good results.
Where drill systems disturb more soil, he advises growers to focus on establishing a competitive crop as quickly as possible.
“Delaying drilling until late March or early April when ground is warmer can work, but it isn’t always suitable especially if you’re disturbing more soil as it simply encourages a flush of black-grass at the same time.
“You may be better drilling earlier at a higher seed rate when conditions are cooler and black-grass isn’t growing to ensure the crop is in the ground and ready to go as soon as it warms up.”
Spring black-grass control tips
· Map problem areas now ready for treatment
· Apply post-ems early when weeds are small, but…
· Ensure weeds are actively growing
· Don’t overlook any areas of poor autumn control
· Minimise soil disturbance when drilling spring crops (5cm depth max)
· Consider the wider spectrum of weed control available beyond black-grass.