Herbicide-resistant plants spreading in 'tillage triangle'

Precision, timing and holistic approach to pest control will be key, writes Louise Hogan

File photo
File photo
Louise Hogan

Louise Hogan

Herbicide resistant plants have been identified in every county in the 'tillage triangle' with moves afoot to raise awareness.

Tillage farmers are being urged to put increasing emphasis on Integrated Pest Management (IPM) with the loss of important sprays through developing resistance and also through the regulatory process at EU level.

Jimmy Staples, head of Teagasc's Enable Conservation Tillage, said there was now resistance identified in most of the main arable counties.

"You could go from Louth to Wexford and across to Cork and within that triangle there is herbicide resistance black grass, sterile brome and wild oats," said Mr Staples.

However, he said that while it was concerning it was not a matter for panic at this stage. Mr Staples said it all goes back to putting in place IPM protocols on farms to help deal with resistance.

"We want to build awareness so farmers can make informed decisions based on early and accurate identification of a problem," he said. Mr Staples pointed to the UK where the issue with prevalence of black grass is now a huge problem.

Mr Staples said there was a considerable volume of research being carried out in the area in Teagasc with PhD researcher Ronan Byrne examining resistance.

Out of 36 samples of wild oats randomly selected through the county of Wexford some 55pc were resistant to either Foxtrot, Axial or both.

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Farmers were urged at the Teagasc Winter Crops Walk in Oak Park, Co Carlow to jump down out of the tractor and make sure they walk the fields to see first hand the types of weeds and disease prevalence.

Teagasc crops specialist Shay Phelan said Integrated Pest Management (IPM) was key to future planning as he pointed out plotting the level of weeds on a map can help inform planting decisions for the season ahead.

IPM is already a key requirement under the Sustainable Use Directive for Pesticides.

However, its importance is increasing with the loss of important actives through development resistance and through the regulatory process at EU level.

Mr Phelan pointed out that people must put it out of their heads that because they used a product last year that they should automatically use it this year. He said many were using the same actives "year in, year out" which can lead to herbicide resistance build up.

Steven Kildea, cereal pathologist at Oak Park, pointed out as farmers assess winter wheat plots in advance years like this, they must carefully assess plants to ensure they are aware when the plant reaches the three-leaf stage to make certain they get their fungicide application timing correct.

"If there is one investment that everybody should make this year, it is for a hand lens or a magnifying glass. Getting out and unrolling the leaves. That is going to be absolutely critical because fungicides are not sufficient to provide us with the flexibility in our timings so we have to get those timings right," said Mr Kildea.

Michael Hennessy, head of Teagasc Crops Knowledge Transfer department, warned that even though crops may have been sown at the same time around the farm, it does not mean these varieties will reach the three-leaf stage at the same time.

He said the aim is to apply the first major fungicide when the majority of the crop is at the three-leaf stage. "You have to get out, you have to get down off the tractor and dissect it."

Mr Hennessy urged growers to keep an eye on the Teagasc Crop Report updates as they would help with guidance.

Growers were also urged to break out their inner graffiti artist and use a spray can to cover the crop with paint similar to the area the sprayer would have covered on the same day as applying the fungicide.

It means that when you return for the flag leaf application that you know what leaves the sprayer covered. Farmers were told it was an important IPM tool to help time the second application and will indicate if the first spray was too early or too late.

Lodging is a concern this year following the mild winter. "It is just a 'health warning' when you see thicker crops," explained Teagasc tillage specialist Ciaran Collins. Over 75,000ha of winter barley is in the ground this year, the highest figure ever on the back of last year's demand for straw plus a mild October.

Mr Kildea urged farmers to ensure they were not reliant on just one active ingredient for a disease and use a combination product.

Teagasc's Richie Hackett stressed there is no yield advantage of going out with fertiliser in late February as opposed to early March. He said the crop might visually appear greener but trials have shown the yield benefit isn't there. It was also pointed out that early fertilising can increase the risk of lodging. "The last thing you want to be doing is looking at a soft crop in mid March," he warned.

The warm mild weather also increased the chances of take-all but trying to predict if the risk is higher overall is a "mug's game", said Mr Hackett. "A lot depends on what happens over the next three months."

On oilseed rape, Mr Kildea warned growers to check for light leaf spot as it was visible on plants in Oak Park.

 Winter barley

Establishment is excellent following good sowing conditions last autumn and a mild winter.

Management decisions should be made on the basis of shoot counts. Aim for 1,100-1,200/m2 shoots (2 row) for maximum yield.

Mildew present in many crops. Earlier than normal ­intervention should only be required if tiller loss is a large risk.

Weed control: tidy up needed in many crops (fumitory, groundsel, cleavers, etc).

Early nitrogen management vital to maintain yield potential.

Target first N from mid-tillering, early-March, but before GS 30. Crops >1,200 shoots delay N to reduce lodging risk.

Early application of phosphorus is critical at index 1 and 2.

Winter wheat

Establishment is excellent in the majority of cases.

Disease is evident in many crops, especially septoria and some mildew yellow rust in susceptible varieties.

Avoid applying triazoles ­before third last leaf has emerged.

Delay first N till GS 30 where crops are well established.

Autumn-applied herbicides worked well, but tidy up required for some broad leaf weeds and grass weeds.

Winter oilseed rape

Large variation in GAI. Early planted ungrazed crops GAI up to 3.0. Lower GAI's (05) due to pigeon grazing.

Total applied N and timing should be based on GAI.

Target GAI of 3.5 at start of flowering to deliver maximum yield.

Apply fungicide now for light leaf spot as soon as symptoms appear.

Forward crops (>1.0GAI) will benefit from fungicide with growth regulatory properties at green bud stage.

Winter oats

Establishment is excellent.

Early planted crops are very advanced (GS 31), and recent frost may have damaged the ear.

Mildew is evident in most crops, but recent frost has slowed development.

Best shortening effect will come from growth regulator application at GS 32.

Delay first N application on advanced crops. Trials show no significant yield penalty when first N is delayed.

Herbicide has not been ­applied to the majority of crops.

Indo Farming


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