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How adjuvants help give your applications the edge

Ornamentals Advisory Blog
16.03.2020

Our Art of Application programme is all about getting the best result from every spray you apply to your crop ­– making every drop count, if you like. Pairing the right adjuvant with your pest or disease control product or plant growth regulator is going to become an increasingly important aspect of that.

 

Why? Because in today’s world of ever-tighter restrictions on rates and how and when to apply, the right adjuvant can help to get more of the active ingredient onto the target, make sure it stays there, and in many cases enhance its uptake too.

 

Adjuvants are also likely to play more of a role in broadening the range of crop protection products available to you to select from, through optimising the performance of those that might otherwise be regarded as less effective than you need. As biopesticides become more widely used it could be critical to partner them with appropriate adjuvants for adequate performance.

 

Managing spray volume rates can a particular challenge in ornamentals. If you’re looking to use a lower spray volume without compromising on results an appropriate adjuvant may help. But an adjuvant can also be useful if you have to apply higher volumes with the active at a relatively low concentration.

 

Some adjuvants will also enable you to use coarser droplets, which can help the spray to penetrate into a dense crop canopy.

 

Most crop protection products will include in their formulation an adjuvant of some sort, but tank-mixing with an additional specialist adjuvant can help you tailor more closely the activity you’re looking for. That’s particularly important in ornamental crops as few pesticides are specifically developed for them in the first place.

 

The range of adjuvant options can appear confusing but, just as when deciding which fungicide, insecticide or plant growth regulator to use, it comes down to the job you want it to do and the mode of action that will achieve your aim.

Break the tension

One of the key challenges to good control on ornamentals is the crop’s diversity of foliage ‘architecture’ and texture – hairs and waxy cuticles on the leaves are effective waterproofing. Parts of the target pest or disease can make it difficult as well ­– fungal hyphae and insect bodies can be fairly water-repellent. Some adjuvants overcome this because they’re designed to reduce the surface tension of spray droplets.

 

Surface tension is what keeps a droplet intact but it’s also what makes it bounce when it hits a surface. Adjuvants formulated to reduce bounce contain various kinds of surfactants, often based on organic compounds, to lessen surface tension. The droplet deforms more when it hits the leaf, absorbing energy and wetting the surface rather than bouncing off. Some adjuvants make the droplet more viscous too, which helps dissipate its energy on impact.

 

Anionic surfactants based on fatty acids and similar compounds are good at reducing the ‘contact angle’ between the surface of the droplet and the leaf, helping the droplet to spread and preventing it from ‘sitting proud’ on hairy surfaces.

 

Stuck fast

A couple of other adjuvant actions can be helpful for ornamentals.

 

Products containing ‘stickers’ or extenders help retain the active ingredient on the surface, giving it more time to be absorbed and making it more ‘rainfast’ ­– useful for protectant fungicides or insecticides and when you’re trying to manage spray operations in changeable weather or wanting to irrigate. Bear in mind, though, stickers can impede uptake of systemic products and check the label or EAMU notices on your fungicide, insecticide or plant growth regulator which may include advice on appropriate adjuvants to use.

 

Adjuvants designed to improve uptake can help overcome the barrier of a leaf’s waxy cuticle. My colleagues at Syngenta’s Jealott’s Hill international research centre say there is good evidence for the presence of ‘channels’ through the cuticle; adjuvants that maintain water-soluble materials in a liquid form enable them to pass through these channels more easily.

 

Adjuvants containing humectant compounds, such as sugars or glycerol, not only can keep water-soluble materials in a liquid form but also reduce droplet evaporation, both ‘in flight’ and after landing. That property makes them especially valuable when you need to apply smaller droplets, and to increase absorption of systemic products including plant growth regulators.

 

The pros and cons

There’s a balance to be struck with some of these adjuvant properties. Overdoing the wetting or spreading, for example, can lead to excessive run-off which defeats the object. And enhancing the performance of an active ingredient may make phytotoxicity more of a risk on some crops – by increasing the amount taken up through the leaf cuticle, for example.

 

That’s why, as with any crop protection application, it’s good practice to test your intended combination of product, adjuvant and dose on a small scale before applying to a crop for the first time. We and our suppliers can advise you, too, based on the results of our extensive trials experience.

 

In the next article I’ll report on a trial last year on a well-known UK nursery where we tested two new Syngenta adjuvants in combination with different approaches to nozzle selection and application rate, to see how coverage can be improved.

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