Getting winter crops off to a weed free start is crucial to achieving healthy, high-yielding crops. It’s vital your pre-emergence herbicides are effective despite challenging weather conditions, should they arise.
The weather can significantly jeopardise the effectiveness of residual herbicides, putting crop establishment, plant health and a successful harvest at risk. While we can’t control the weather, there are workarounds to help minimise the weather working against your pre-ems. Consider the following strategies this autumn:
Key points:
- Prepare the soil well
- Monitor soil moisture
- Plan around weather forecasts
- Avoid extreme conditions
- Know your pre-ems
- Apply during calm weather
- Be prepared to adjust strategies
- Utilise Backrow Max to mitigate the issues
Prepare the soil well
Ensure a good seedbed to promote effective herbicide infiltration and minimise the risk of runoff in adverse conditions.
Well structured soil is crucial to the performance of residual herbicides and is characterised by a good tilth, no compaction and good porosity.
A firm fine tilth – will enable good distribution of the residual herbicide when it is sprayed across the soil surface.
Removal of any compacted layers – is vital to allow good water and herbicide infiltration into the soil, down to the weed germination zone.
Healthy soils with good porosity – not only keeps the soil aerated for your crops, it also directly affects the volume of water your soil can hold on to. This has implications for crop health and residual herbicide efficacy.
Monitor soil moisture
Ensure adequate moisture levels in the soil for effective herbicide activation and uptake.
Soil moisture – is the carrier for getting your residual herbicides from the soil surface to the weed germination zone. It is also an enabler for efficient adsorption and desorption of herbicides from soil particles for uptake into germinating weeds.
Therefore, before you apply your pre-ems assess soil moisture levels. Consider delaying drilling and applying pre-ems during a dry spell, particularly if there is insufficient moisture for weeds to germinate shortly after application.
Time applications
Plan around weather forecasts: Apply pre-emergence herbicides when rain is forecasted in the following days to ensure adequate moisture, but avoid periods of intense rainfall.
Avoid extreme conditions: Steer clear of applying residuals during periods of heavy rain. Heavy rainfall shortly after application can wash herbicides faster through the weed germination zone – the top 5cm – where they are needed to control germinating weeds.
Periods of intense rainfall can result in saturated soils and lead to leaching.
Under intense rainfall herbicides move more quickly through the top 5cm of the soil, with reduced adsorption to soil particles. This results in a sub-lethal dose of herbicide retained in the weed zone for effective weed control. There is also a higher risk of damage to the crop seed and contamination to groundwater.
Know your pre-ems
Choose complimentary chemistries to help deal with different weather conditions.
Soil temperatures influence herbicide half-life: In warm dry soils, herbicide degradation is faster and your herbicide may run out of steam quicker than you expect. Plan drilling and herbicide choices to ensure herbicide longevity is optimised around weed germination.
Water solubility and Kfoc affect activation and retention in the weed germination zone: In dry soils, herbicide actives with high water solubility and low adsorption to soil particles will be activated faster. They will also move into weeds more efficiently compared to herbicides with low water solubility and medium-high adsorption.
But in wet soils, herbicides with high water solubility and low-medium adsorption to soil particles will move faster through the weed germination zone with heavy rainfall, reducing residual activity. Herbicides with low water solubility and medium-high adsorption will be retained better.
Stacking herbicide actives with different characteristics will help manage different moisture scenarios to optimise efficacy and crop/groundwater safety.
Apply during calm weather
Choose days with low wind speeds to minimise spray drift and ensure even application.
Pre-emergence applications are particularly susceptible to drift due to there being no crop to intercept the herbicide.
Drift reducing nozzles will help protect off-targets, though the coarse spray droplet may impede full even spray coverage of your soil target due to the bigger droplet size.
Be prepared to adjust strategies
Keep an eye on conditions: Stay informed about weather forecasts and be prepared to adjust strategies as needed.
Consider pre- followed by peri-emergence applications: Focus timing of your residual herbicides to the emergence timing of your weeds. Following up with a peri-emergence application around two weeks later will help to control new flushes and top up your herbicide concentration in the weed germination zone.
Utilise Backrow Max to mitigate the issues
By incorporating residual herbicide adjuvant Backrow Max into your pre- and peri-emergence tank-mixes, you can significantly improve the reliability of your pre-ems during adverse weather conditions. Here’s how it can help:
In dry conditions: Backrow Max helps maintain soil moisture levels in the soil, reducing dependency on rainfall for herbicide activation. This also aids the consistent release and uptake of herbicides into germinating weeds leading to more effective weed control.
In wet conditions: Backrow Max helps bind herbicides better to soil particles, reducing their movement out of the weed germination zone. This prolongs herbicide concentration and longevity in the weed zone following heavy rainfall, increasing both herbicide effectiveness and residual activity.
Backrow Max reduces the risk of herbicides reaching the crop seed damaging plant health, and minimises contamination to watercourses. It safeguards crop establishment and is a valuable water stewardship measure.
In drifty conditions: Backrow Max reduces the number of fine spray droplets under 100 microns which are the most susceptible to drift. It also reduces the number of very coarse spray droplets prone to bounce, creating a more optimal spray droplet for pre-emergence application. This results in more even spray distribution and coverage across the soil surface creating a more effective barrier to weeds.
Stop the weather working against your pre-ems with Backrow Max
Adjuvant Backrow Max not only ensures maximum placement of pre-ems where they are needed, it also helps ensure they work as hard, and for as long, as possible.
Download our latest guide here – for independent trials results with the latest herbicides, and farmer case studies. You’ll also find an extensive list of approved crops.
Please get in touch with Stuart below if you require any technical assistance.
Backrow Max can be purchased through Agrii in the UK.
At the cost of a pint of beer, its the cheapest black-grass control you can get!
