What are the key properties to look for in an adjuvant?
The waxy cuticle that coats the leaves of most plant species has evolved to do two important jobs: it helps seal the leaf tissues to control evaporation from within and makes raindrops bead-up and run off, keeping the leaf surface clean, dry and inhospitable to pathogens.
When you’re trying to spray your crop, however, that cuticle really works against you. If droplets bead and run off, the active substance goes with them. Even if they don’t run off they can dry without spreading so the active far from covers the entire surface. And unless it remains in solution, a translaminar or translocated active has little opportunity to penetrate the cuticle into the leaf tissue.
Insects have a waxy protective outer cuticle, too. It works in much the same way, with implications for your pest control sprays.
In an earlier blog we talked about the increasing importance of adjuvants in tank mixes. Adjuvants help by reducing the surface tension of droplets so they spread more readily on water-repellent surfaces, giving the active substance a better chance of being absorbed.
With ever-tighter restrictions on application rates and timings, the right adjuvant can make sure more of the active stays on the target, and in many cases enhance its uptake as well. By optimising the performance of actives that might otherwise be regarded as less effective than you need, they give you a wider range of useful crop protection products to draw from.
Using the right adjuvant to help you get the most out of the sprays you’re applying is particularly important when it comes to biopesticides. As we’ve discussed in earlier blogs, we’re becoming increasingly reliant on them but their effectiveness depends on getting all of the product on target, and keeping it there. The same goes for foliar-applied biostimulants such as Hicure.
So what properties are you looking for in an adjuvant that will not only stick your spray to the leaf but ease the passage of the active substance through that waxy cuticle?
Our new adjuvant, Elasto G5, is based on polyglycerol and coconut oil fatty acids. These constituents have been chosen because their molecular structures reduce the surface tension of droplets so they spread onto, rather than bounce or roll off, a leaf surface. They work well with relatively water-soluble active substances – including the amino acids in Hicure, many biopesticides and a range of fungicides and insecticides – which are less likely on their own to dissolve in and move through cuticular waxes. They are also proven to be safe to beneficial insects and have low risks of phytotoxicity.
The performance of plant growth regulators (PGRs) is directly related to the amount of active substance that leaves absorb, so comparing the effect of applications with or without an adjuvant gives a good idea of the adjuvant’s impact.
For example, in one set of trials we looked at August applications of chlormequat to control the height of poinsettia plants. We found using Elasto G5 with a half-rate application of chlormequat had a slightly stronger effect than the full rate of the PGR used alone.
In another set of trials, daminozide was applied to control the height and spread of Surfinia petunias. Three PGR applications were made – on August 14, 21 and 28.
When plants were assessed on September 10, the untreated plants had grown to 14.5cm in height and 55cm in diameter. Those receiving daminozide at full rate and no adjuvant were 10cm tall with a 42cm spread.
At 11cm tall and 44cm in diameter, plants were almost as well controlled by daminozide applied at half-rate in combination with Elasto G5. In contrast, applying the PGR at the same rate but with an organic silicone wetter was unable to keep plant height below 12cm.
Achieving the result you want from a plant growth regulator, while using less active substance, has environmental and cost implications, of course, as more product is retained on the foliage and less runs off to waste.
When it comes to insecticides, fungicides and biological products, however, using the right modern adjuvant is going to be increasingly important as we look to squeeze every last drop of effectiveness out of them.
But while an adjuvant improves the results of good spray technique, it’s no cure for poor application.