All crops are now responding well to the improved weather conditions that have impacted across the country over the past week and growers therefore need to think about how they are going to control weeds.
For tillage crops, it’s either all in or not at all, where their management is concerned.
Farmers cannot afford to do a half or mediocre job. The only end result from this approach is a combination of poor yields and significant losses.
The latest episode of the ‘Tillage Edge’ podcast is dedicated to the subject of controlling weeds in spring cereal crops.
How to control weeds
Profitability only comes when yields are high and weed control is a key driver in this context.
As a rule of thumb, 98% weed control must be achieved within any crop. Only in this way will the crop be allowed to meet its full yield potential, while also ensuring the future weed seed burdens are minimised.
According to Teagasc tillage specialist, Ciaran Collins, all later sown spring barley crops are now at a development stage where weed control strategies should be implemented.
He said: “There was a three-stage sowing of spring crops this year. We had some very early crops sown out at the end of February. This was followed by a small amount of planting carried out around easter.
“But the vast bulk of the spring planting work was carried out at the end of April.”
This last crop category is now at the four- to five-leaf stage. In addition, a nice spread of weeds is now evident.
As a consequence, a lot of these crops are ready to be sprayed now.
“Herbicides have their best effect when applied to an actively growing weed,” Collins said.
“So, if a weed has been rolled or damaged by wheel tracks, it should be given time to recover.
“There is tremendous growth at the moment. So a week or 10 days will give weeds an opportunity to regain their full growth momentum.”
Weed control mix
The essential weed control strategy recommended by Teagasc for use on spring cereals includes a sulfonylurea in tandem with a suitable mixer product.
“Options here include two actives. This approach reduces the resistance risk,” Collins continued.
“The partnering products should also reflect the specific weed populations that are in the field.
“Most likely, these will include speedwell, chickweed groundsel and fumitories. So a good, strong-spectrum partner to the sulfonylurea is advised.”
Collins explained that application rates are also critically important. These must be appropriate to the weed sizes in the fields.
“There is scope to reduce rates if small, actively growing weeds are being targeted,” Collins said.
“But the amount of herbicide sprayed must be sufficient to knock out the weeds that are present.”
According to the Teagasc representative, Irish growers can choose from a good selection of herbicides.
“This helps to reduce the threat of resistance developing within weed populations,” he stressed.
“It really is a case of picking the herbicide mix that is appropriate to the specific crop and the weeds within it.”
Where wild oat control is concerned, Collins advised that the specific herbicide required to do this job (most likely Axial) can be mixed with a sulfonylurea and a partner product – not a hormone.
The only consideration here is that the application rate must be a minimum of 0.6L/ha.
One downside to wild oat management is the fact that the seeds will be found at a range of soil depths. This will result in a range of germination dates.
“This means that some wild oat plants can be up to two growth stages behind the actual cereal crop,” Collins continued.
“However, if current spring barley crops are left until the four- or five-leaf stage prior to spraying, this should give effective cover against wild oats.
“The only case for delaying a herbicide application is if the presence of canary grass is suspected. This can be quite a slow growing weed. But the longer the delay, the greater is the risk of a reduction in herbicide coverage.”
Choosing products
Teagasc tillage specialist Shay Phelan also contributed to the podcast. He confirmed the importance of matching herbicides with the range of weeds within a specific crop.
“Not every product is going to control every weed,” Phelan said.
“This is why it is so important to select products that match the actual weed burden that exists within a crop.
“E.g., we know that a product like Cameo Max does not control cleavers. So it is important to include a partner product in the tank mix that does.”
However, Phelan went on to make the point that Cameo Max no longer gives control over chickweed.
“However, the product did deliver this level of control when it was first launched. Over time chickweed had developed a resistance to this herbicide,” he explained.
“This has come about because application rates were not adhered to in tandem with the possible overuse of the product down through the years.”
Phelan highlighted chickweed, poppy and corn marigold as the three broadleaf weed types showing the highest level of herbicide resistance at the present time.
Where grass weeds are concerned, blackgrass and Italian ryegrass are giving cause for concern.