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Crop Advice & Expertise

6 Steps for post-em success

After a mixed autumn, many wheat crops will need a follow up spray to control a wide range of weeds such as black-grass and brome. Here are 6 tips to achieve the best result.

 Wintery weather has delayed the start to post-em applications but farmers need to be ready to spray as soon as conditions improve.

1. Assess field conditions

Most land is still not in a fit state to travel so now is the time to check crop condition and weed levels to plan spring herbicide applications. According to Bayer’s Darren Adkins, there is a lot of variability in crop condition, weed levels and control achieved by pre-em herbicides. Pay careful attention to weed species and distribution so the right product can be targeted at the right area. Pay attention to the resistance status of black-grass and ryegrass. Plants with metabolic resistance are still susceptible to treatment at early growth stages.


2. Product choice

Farmers have a range of products to choose from in spring. Pacifica Plus (mesosulfuron + iodosulfuron + amidosulfuron). Has the widest spectrum of activity controlling grass weeds and many broad-leaved weeds including cleavers. In situations, with only black-grass or brome issues, Monolith (mesosulfuron + propoxycarbazone) is also an option. Fields with meadow-grass problems that missed the autumn pre-em spray can be cleaned up with Othello (mesosulfuron + iodosulfuron + diflufenican)

After a mixed autumn, many wheat crops will need a follow up spray to control a wide range of weeds such as black-grass and brome. Here are 6 tips to achieve the best result:


3. Application timing

“With any contact acting herbicides against black-grass the principle has to be if the target is there and you can spray, then get it done because smaller plants are more susceptible. The exact date doesn’t matter as long as conditions are in your favour and you comply with the label,” says spray application specialist David Felce of Agrii and Midloe Grange.

But during early spring farmers have to pay close attention to conditions. Active growth is absolutely essential because it means the plant will absorb the active into the leaf cells where is gets to work.

Drying time is also important, the minimum drying time is 2-4 hours because  rain or dew can wash off the herbicide leaving weeds unscathed. Bright conditions with a light breeze are ideal, although if no rain is forecast and it is well before dusk and dew formation than it is safe to spray.


4. Application technique

“There are so many variables when spraying, the conditions will never be ‘perfect’. The thing to remember is get as many things right as possible.”

Once conditions are suitable to spray, the onus is on the operator to ensure the set up gets the best possible result.  Droplet size and distribution both depend on nozzle choice and operation.

“In open crops in early spring, I favour a 03 flat fan nozzle as it produces a smaller droplet size with even distribution. This means the herbicide is likely to reach the target and settle on the leaf.

“With this type of nozzle, you have to watch forward speeds; too fast and the pressure becomes too high, creating a fine spray that doesn’t have the weight to fall and adhere to the target.”

Any spray windows are likely to be short at this time of year, so Mr Felce suggests farmers to consider reducing water volumes. “In open crops 100l/ha is sufficient to get good coverage. As the canopy develops during spring this will have to increase to 150l or 200l.”

For all applications a boom height of 0.5m above the canopy is a good starting point although the technology on some modern sprayers can safely go lower.


5. Only tank-mix if necessary

Contact acting herbicides are most effective when applied as a single product with a suitable adjuvant such as biopower. If workloads dictate that a tank mix is necessary, use tank-mix sheets to ensure physical compatibility.


6. Long-term plan

A spring post-em is just one step in a long-term plan to control black-grass. All the plants controlled in spring will not shed seed in summer and create problems for future seasons. Even though, reduced sensitivity has made post-ems less effective in many instances, they can still provide 50-60% control.

As a result, there will be fewer seeds to control next autumn meaning there is less pressure on the other cultural and chemical control measures in the rotation.