Rise in fall armyworm numbers
Populations of fall armyworm are two to three weeks more advanced than they have been in previous seasons, bringing calls for maize and sweetcorn growers to scout their crops as often as possible.
He is exhorting New Zealand arable farmers to get into mechanical weeding now rather than wait until they too have no choice.
"You are far better off to get into mechanical weeding to protect the herbicides you currently have, to keep them going so you don't lose them to resistance, and only have mechanical weeding as your option.
"Integrating mechanical weeding and herbicides is the smart thing to do now."
The head of the Lincoln-based Future Farming Centre, Merfield was a speaker at the recent FAR CROPS Expo at the FAR research site at Chertsey, where attendees were given a demonstration of a newly-acquired mechanical spring-time weeder.
Based on a show of hands, only a few attendees knew they already had herbicide resistant weeds on their properties, but Merfield said that, based on the genetics and the size of weed seed banks, everybody did.
"Even organic farmers have herbicide resistant weeds. They can't find them because they don't use herbicides."
Globally the problem of resistance continued to get worse, while the last new mode of action was the Acetolactate synthase (ALS) herbicides in 1983.
“We’re losing herbicides: to resistance, to legislation, and increasingly to customer demand. Your options are only going to decrease.
“So we need to look after your chemicals. If you look after your chemicals, your chemicals can continue to look after and support you.”
The answer was diversification – of crops and rotations, and of herbicide types.
“The other way of diversifying your herbicides is to stop using them and start using mechanical weeders,” he said.
Merfield said it had been lonely for him “nerding on” about mechanical weeding for 30 years, but Europe was undergoing a revolution and all the big companies were now offering mechanical weeders.
“The good news is this technology has improved in leaps and bounds.”
It also used to be complicated but was now generally standardised around a few basic methods.
The demonstration machine recently bought by FAR was a spring-tine weeder which Merfield said might be the best starter for an arable farmer.
As a contiguous weeder, it applies the same weeding action across the whole field surface, travelling at speed and covering a lot of ground quickly. Shallow rooted weed seedlings are simply uprooted while the more robust deeper-drilled crop plants might get knocked over but generally stand up again.
Farmers might then add a spoon weeder (or rotary hoe to Americans) or an Einboch Aerostar type. All were contiguous weeders but with different modes of action, so they complement each other.
Beyond that was inter-row hoe weeders, which Merfield said were all now largely standardised to what he called a modular parallelogram design.
“What they are is more of a platform on which weeding tools are mounted. This means they’re hugely flexible. You basically choose the right tools for the crop, the growth stage, for the wheat, for your soil, general conditions.”
With camera and GPS guidance systems, speeds of 10 to 20 km/h are standard.
“If you’ve got something that’s 20 metres wide and you’re doing 20 km/h down a paddock, you’re covering ground, you’re not faffing around with this gear anymore.”
There was also a “whole bunch of weeding tools now available”.
“So, you don’t have to go the fancy robots with the lasers and stuff. This big stuff will weed the whole paddock. At speed.”
Weeds Jump Fence
Charles Merfield also outlined studies he was undertaking into alternative means of dealing with fencelines, track verges and other uncropped areas.
He said the way we use herbicides to clear those areas – often repeat glyphosate – was abnormal internationally and illegal in Europe. With bare earth providing no competition from other plants, it encourages resistant weeds.
In Australia, resistant weeds developed in fence lines then jumped into crops, and that was now being seen here.
“This is no longer hypothetical stuff. This is occurring now in New Zealand. This is another herbicide resistance issue we need to get on top of.”
With fences being similar to vineyard structures, arable farmers could consider some of the weeders, mowers and cultivators developed for vineyards.
There were challenges and problems in adapting them to arable farming.
“But the bigger problem is generating herbicide resistant weeds in that space and having them jump into your crops.”
One approach being trialled is filling the uncropped areas with good plants instead than trying to clear the ground.
They are trialling a mixture of perennial brown top, which should do well with low nutrients; the perennial broadleaf garden alyssum for its flowers and nectar to support pollinator species and other beneficial insects that will control crop pests; and broom, for its early spring flowers that also supports pollinators.
“So, that’s what we’ve got as a demonstration trial, but it’s more food for thought for you guys to say, okay, we are doing regular herbiciding of our fence lines now, but what’s another thing we can do here? What’s an alternative?”
