Resistance demonstrated by both grass and broadleaf weeds to applied herbicides is on the rise, according to Teagasc.
Moreover, this rate of increase is growing exponentially.
Teagasc research officer Vijaya Bhaskar discussed these issues on the latest Tillage Edge podcast.
He pointed out that Irish tillage farmers must take greater account of the threat posed by herbicide resistance. This is especially so in the case of acetolactate synthase (ALS) herbicides.
“These products form the basis of the strategies put in place to deal with broadleaf weeds,” Bhaskar explained.
“We have started to survey cases of resistance demonstrated by weeds to ALS. To date, we have identified two such cases in counties Meath and Kildare, both involving poppies.
“Of great concern is the fact that the weeds identified demonstrated very high levels of resistance. The plants in question survived rates of herbicide application that were well above those recommended for on-farm use.
“Given current circumstances, it is unlikely that a single herbicide will ever give full control over poppy in those problem fields,” he added.
Resistance
Bhaskar also confirmed that blackgrass resistance is also a growing concern on many Irish tillage farms.
In light of these developments, Teagasc is now surveying the use of all ALS herbicides in Ireland and their specific predisposition to ‘target site’ resistance.
Wild oats is a specific problem in many spring cereal crops. According to Bhaskar, three types of resistance-related problems arise, where this specific weed is concerned.
Of greatest concern is the fact that 20% of Irish wild oat populations are cross resistant to most acetyl coA carboxylase (ACCase) herbicides.
“Canary grass is another problem weed in a continuous spring cropping scenario,” Bhaskar continued.
“However, a product like Axial will provide good levels of control when applied at the recommended rate.”
The Teagasc representative highlighted the role of a spring break-crop option, in helping to control weeds such as wild oats.
In these circumstances, a graminicide can be used with a high degree of confidence. However, where resistant wild oats present a challenge, Stratos Ultra (cycloxydym), will be the herbicide of choice.
Teagasc supplies a free testing service to growers who think they may weed resistance problem.
This is particularly the case if blackgrass is identified within a crop. All fields should be considered as suspect. The same principle holds if Italian ryegrass and bromes are identified within a crop.