Weed out the competition
Left unchecked, weeds can soon outcompete a crop during its early growth stages so it’s important to take care of any yield robbing weeds as we head in to spring. But weeds can be challenging targets for post-emergence herbicides and you may need an adjuvant to secure success.
Management strategies should consider weed biology, herbicide active ingredient properties and weather conditions. Here’s our advice on why and how adjuvants could make the difference to your weed control this spring.
Reasons to incorporate an adjuvant:
- High pH could deny you 30% efficacy
- Cold water makes mixing slow & difficult
- >3 products in the tank heightens the risk of a mixing problem
- Good coverage is crucial but often an issue
- Most post-em herbicides need an adjuvant for effective uptake – you could be missing out on 40% control
Check water quality and correct high pH
Don’t underestimate the impact of high pH on herbicide performance – the conditions in which you create your spray mixture affect its stability in the tank and availability to plants.
High pH can break down some herbicides through a process called alkaline hydrolysis. The more alkaline the water, the faster the breakdown. SU chemistry is most stable at pH7. If you’re tank mixing with other crop protection products keep in mind most are stable at pH6.
If you don’t already know the pH of the water you use for spraying, our advice is to test it. A pH of 6-7 is optimal for most products you’ll be adding to the tank so if its off, its worth adding a buffering adjuvant such as Kantor that will take pH to 6-7, before you add your crop protection products.
Note: If you’re spraying off stubbles with glyphosate ahead of spring cropping, you’ll need a glyphosate water conditioner to achieve pH5 and to sequester hard water cations that may be present. You can find out more about the effects of hard water and high pH on glyphosate here.
Optimise product mixing & compatibility
Early spring tank mixes can be challenging. Water is cold, and this slows the mixing process, especially with powders and water dispersible granules.
Mixes could also be hefty and complex. As well as post-emergence herbicides, you could be adding an early season fungicide, PGR and nutrition. By T1, you could have a 7-8 way mix, that all must dissolve and remain stable in the mix together, so all active ingredients can be taken up by your plants. Failure to achieve this wastes expensive products and puts crop safety and your sprayer at risk.
Adding a compatibility adjuvant such as Kantor, can help emulsify the mix, so mixing is easier, faster and products remain thermodynamically stable over time. This can be particularly beneficial with nutrition which can be notoriously difficult to dissolve, as shown in the video opposite.
Using low water volumes? Improve coverage
With a busy spring workload, you may be using low water volumes of 100 L/ha, but keep in mind that whilst this will allow you to spray more hectares, it will reduce coverage compared to higher water volumes.
Good, even coverage is essential for post-emergence herbicides so it is wise to either reduce forward speed, or consider a spreading adjuvant (such as Kantor or Sorrento) to improve coverage across target plants.
Control drift AND consider coverage implications
Controlling drift is not only crucial to protect the environment, on target application is also crucial for weed control success.
Drift reducing nozzles will of course help minimise drift, but the coarser droplets they produce can reduce coverage and retention. So, even if you are using DRT, don’t forget coverage.
Field scale trials have shown that DRT + adjuvant Kantor is best for drift reduction and deposition/coverage. Kantor manipulates droplet size at either end of the droplet spectrum – it removes the ultra-fine droplets prone to drift and the very coarse droplets which are prone to bounce, resulting in a more uniform droplet for optimum deposition and coverage across target plants.
Target weeds when small & maximise coverage
Taking out troublesome weeds should be a key priority early spring as weeds are best controlled when they are small – cuticles are easier to penetrate and weeds are less able to detoxify the herbicide.
If sprays become delayed and weeds get larger, it’s important to consider the impact on herbicide coverage and uptake. As weeds get larger there is a greater risk of poor control.
The challenge arises because water and oil don’t mix well – applying your spray to a waxy leaf causes high surface tension which leads to beading on the leaf. This is because leaves are hydrophobic, meaning they repel water. It means that unless you reduce surface tension between your spray solution and the leaf surface, coverage will be compromised. You might get away with it when weeds are small, but not at larger growth stages.
This is a key reason for including a suitable adjuvant, such as Kantor or Sorrento, to help reduce surface tension so spray droplets can spread out across the whole leaf – contact herbicides must be in full contact with the whole leaf surface to kill weeds as they do not move inside them.
Know your weeds – coverage can be tricky
Have you ever noticed that weeds which are very waxy, and hairy like Bur Chervil are even harder to control?
That’s because with a waxier leaf, spreading is even more difficult to achieve and leaf hairs reduce leaf:droplet contact.
So if you’re tackling any particularly difficult weeds this spring, adding an adjuvant such as Kantor or Sorrento will most definitely help lower the surface tension so optimal coverage and control can be achieved.
Uptake is the final & most challenging hurdle
Effective uptake is the most challenging step for post-emergence herbicides. Many of them have high water solubility, and yet, they must penetrate the waxy leaf cuticle which covers the whole plant to move inside.
Herbicides with high water solubility struggle to enter leaf cuticles because the waxy cuticle is designed to keep water out. The table (right) shows water solubility for the most common post-em spring herbicides is high. Many SUs for example, have high water solubility and need an adjuvant to work effectively. BUT, pairing your herbicide to the right adjuvant is key. Herbicides with high water solubility need a hydrophilic adjuvant – like Sorrento, adding as much as 40% efficacy to overall weed control.
Herbicides with moderate water solubility (- see table left for examples) can also benefit from an adjuvant, especially on larger weeds which have tougher cuticles and in cold/dry conditions.
You can look up other herbicide actives here. Click on the active ingredient you are interested in and scroll down until you find water solubility.
Herbicides with low water solubility need less help to penetrate but entry can be spead up with a lipophilic adjuvant. Examples would include Toil or Kantor.
So what do you do if you’re using herbicides with different water solubilities, or your tank mix includes a fungicide/PGR? Adjuvant Kantor has a unique mode of action. It increases the packing density of active ingredients at the cuticle. Entry is by diffusion so Kantor benefits active ingredient uptake of all types. It also has a multitude of other benefits you can take advantage of, as we established earlier.
Trials demonstrate just how much adjuvants could bring to your weed control this spring
Adjuvants could make a big difference to your weed control
Selecting the right adjuvant for your herbicide can deliver significant performance benefits, particularly when it comes to herbicide coverage and uptake. Before selecting an adjuvant make sure you know where the issues might be and what you need to achieve. Our summary table right, gives a few pointers to help, and you should always check the herbicide label for any additional advice.
If you have any technical questions, or need some advice on how adjuvants could help benefit your weed control, please get in touch with Stuart below.
