Herbicide formulation: How we maximise effectiveness in the field

Stubborn weeds such as black-grass put huge demands on herbicides to perform each season. Herbicides depend on the active substances reaching the target – usually a leaf or the soil – but getting the active there is no easy matter. Over each hectare, just a few grams of active need to be spread accurately and evenly so that weeds are controlled across the field.

Good application technique and suitable conditions play a part, but in any herbicide there is ‘hidden technology’ in the formulation. Long before the herbicide reaches the field, Bayer’s formulation experts make sure farmers get the most from every active they are using.

“When formulating herbicides we have two main aims,” Dr Roechling explains:

• Make sure the active substance can reach its target and take effect – for example to be absorbed into the leaf

• Allow the product to be stored and handled safely and effectively

“If not formulated properly, active substances can react or degrade so that the herbicide does not provide the expected level of activity when the farmer uses it.”

Ultimately, the chemistry of the active substance determines which formulation type can be used. “It is difficult to change the fundamental properties of an active substance with formulation, what we try to do is get maximum activity for the smallest possible dose,” says Dr Roechling.

Balancing activity with stability

Theoretically, the best activity is achieved from having the smallest possible particle size for the active substance, particularly for herbicides that need to penetrate the leaf. However, small particles may be more likely to react, be light-sensitive or show crystal-growth, so the challenge is to balance activity with stability.

“Many substances are reactive with water so in these instances, instead of a water-based suspension concentrate (SC), we prefer an oil dispersion (OD) or a granule (WG) for better shelf-life. In an OD the active is protected by the oil, which additionally helps the active after application to penetrate into the leaf. When successful, the OD formulation manages to deliver the needed amount for the best biological activity of the active.

“For soil-acting herbicides, things are a bit different. Larger molecule sizes are often preferred to prevent rapid degradation. Longer-lasting stability on the soil is required so that the active is encountered by germinating weeds. Formulation means we need to balance these different requirements.”

One ambition for the team is to find a way to improve flufenacet activity in situations with low soil moisture. Doing so would greatly increase flexibility for growers using flufenacet-based products like Liberator, but the research is still in the early stages.

Improving performance

For farmers, the big question is whether new actives or formulation techniques can provide a substantial improvement in weed control.

At present, Dr Roechling is not anticipating any significant revolution in formulation technology, but the Bayer team continues to systematically improve the physical and chemical stability, and also the biological performance of their products.

Research is continuously looking for new actives that have a high impact on weeds, including resistant ones, but these are more and more challenging to find and register.

“We get involved in product development at quite an early stage. After a researcher has demonstrated the activity of a new substance in glasshouse trials, we come in to assist. We develop ‘research formulations’ as soon as an active is to be tested in plot trials.”

At this point, Dr Roechling and his team need to use all their skill and experience to ensure that the active is given a fair test and has every chance to prove its best value as a herbicide. Deciding on these research formulations depends on the properties of the active.

“Typically for herbicides we don’t think about single molecules when making formulations because safeners and other additives are an essential part of the product – it is very much a case-by-case basis.”

Managing resistance

Dr Roechling is keen to stress that formulation alone is not a solution to many of the challenges herbicides face; with herbicide-resistant weeds, formulation can only play a limited role in tackling the problem.

“Formulation can do very little to manage resistance directly – this is related to the interaction between the active substance and the target organism. However, using the most effective herbicide treatment is important, so a well formulated product will help.”

One way Dr Roechling’s team can help is by developing co-formulations of actives so that farmers can use one product with two or more actives that help one another. Mixing modes of action is a very good resistance management strategy and co-formulations help farmers to apply this in one hit. But creating a co-formulation is not easy, he says.

“Not all active substances are suitable for co-formulation together. For example, different actives may be stable at a different pH or need very different storage conditions. As a result some co-formulations use actives from the same chemical group such as mesosulfuron + iodosulfuron (Atlantis OD) because they may share many characteristics.”

Overcoming other challenges

Formulations also have a positive influence on reducing drift, avoiding wash-off after rain and the uniform distribution of small active amounts on the field. With these parameters there are good options to make products as safe and efficient as possible.

But turning to regulation, Dr Roechling emphasises that clever formulation is unlikely to overcome the regulatory challenge herbicides face: “If a product is removed from the market due to higher hurdles on the ecotoxicity-profile of an active, it is unlikely to return in a smarter, safer formulation.”

Another buzzword in ag-chem is nanotechnology – for herbicides this means having active substances milled down to the smallest possible particle. Dr Roechling is aware that researchers are experimenting with this but suggests caution before listening to the hype: “Producing small particles is not a technical challenge, the problem is keeping those particles at their produced size,” he explains.

Uncontrolled particle growth during storage can be a common problem and reduces activity severely, even below the activity of standard particle size. We know small particles can be the most effective but there is always the challenge of maintaining the original size during storage.

“Bayer has optimised its methods in formulation technology together with biology to deliver the optimum particle size for our products to have the best biological performance through their shelf-life,” says Dr Roechling.

Long-term, precision and robotic applications are likely to change what is required from a formulation, particularly for the end user. As a result, the formulation team has to keep an eye on future application technology as well as what farmers require in the here and now.

Formulation is one of the main reasons our products outperform their generic equivalents. Find out more about why the pesticide brand you choose matters, regardless of the active ingredient.