Seed Treatment Testing Requirements - Lab Scale Treating Properties and Treated Seed Properties

By the time a seed treatment product or treated seed is brought to market it has undergone an array of stringent testing to ensure it will provide its promised breadth of agronomic benefits. Testing is a vast topic with such a broad range of tests available for so many different purposes. It is an important topic to understand because it impacts everyone involved in the process, from the person running the treater and the person planting the seed, to the industry as a whole. 

Most seed treatment specialists are aware of some of the tests that are available, but most don’t know much about what goes on outside their sphere of responsibility. After decades of global experience with many companies and crops, I have experienced the full gamut of seed treatment testing and can offer a valuable “big picture” overview. And if you are looking to bring a new concept or technology to the market it is valuable to understand the full scope of what you will be taking on and what resources you will need, not to mention that a miss can delay introduction by years or result in commercial disappointment.

During product development, there isn’t a specific testing sequence, as there is a lot of back and forth between groups and iterative testing as the development progresses. Categories of testing include: Biological; Lab Scale Treating; Treated Seed Properties; Product Testing; Regulatory Testing; and Scale Up Testing (see the Appendix). This article will cover two core categories: Lab Scale Treating Properties and Treated Seed Properties. Our goal is that this information will encourage those who need it to dig deeper. Undoubtably there will be additional and varying standards out there, and certainly there isn’t just one right answer.

Lab Scale Treating Properties

Many Lab Scale Treating Properties tests are the responsibility of the formulator or other support groups. These tests are primarily intended to verify that the product can be effectively commercially applied, but it’s still a standard to meet before moving into field trials. You should start with a good lab scale treater that is reasonably scalable and has enough adjustments available to accommodate different seeds and treatments. Treating in jars is a good option for preliminary work if you know the proper technique because you can really see what is going on, but you do need a mechanical and automated treater for final testing and more controlled experiments.  

Seed Wetness is the first property you see, and you want it to be in the right range for the crop. Optimum seed wetness can be described as “that which allows the treatment to distribute evenly on the seed before absorbing, but dry enough so that it is absorbed and the seed is dry as soon as it is uniform.” It is rare that this scenario occurs due to the desire to put as much on the seed as possible, which drives the application rates above optimum. Seed wetness is generally gauged using an experienced eye, although someone has probably figured an objective measurement. Drying Time is related and is one of the tests best performed in jars because you can see and hear when the drying point is reached and how sharp the drying step is.  

Bridging is a big seed treatment challenge. Normally, the seed comes out of the treater still a bit damp and is then placed in a bin until the treatment is absorbed. If not performed properly, a solid block of seed can form in the hopper due to the polymers that are included to control dust, or some clumps of seed will remain up in the bin. There are many qualitative methods which vary from company to company.

Wet flow is a popular measurement for judging how seeds will move through a treating system. A less common process aspect referred to as “negative redistribution” may occur on some seed types with some formulations, where the treatment goes from more uniform to less uniform if handled (for example, when left in the treater too long or augured) during or after the drying stage.  Formulations have a big impact on that performance aspect.  

Then there is the matter of dealing with the variability in seed treaters and seed treating conditions.  When you ask the question “how are seeds treated?” and the answer is “every way that you can imagine and some ways that you couldn’t imagine”, there’s clearly a lot of variability. 

Treating temperature is another big variable, and can be anywhere from -30 °C to +40 °C.  You need to define the range relevant for the commercial proposition, and test it to make sure it works for those.  Quality of seed plays a role, and poor quality of seed (such as excessive dust) can cause even the best formulations to fail, but the goal is to be able to treat the typical commercial range of seed quality.

Treated Seed Properties

Currently, treated seed dust is the most important of all properties. It has always been important, but even more so now. Strict adherence to achieving low dust levels, in the author’s opinion, is one of the most important parts of seed treatment stewardship and is a big reason why the use of neonicotinoids has been maintained in North America. The Heubach method is generally the universal standard, although other methods have proven advantages. Given that dust measurement is so important, the seed treatment industry is encouraged to look for other methods, particularly ones that provide at least indirect information on particle size distribution of the dust and/or have a higher sensitivity for accurately measuring lower dust levels.

How well the treatment stays on the seed after drying and handling is similar to the dust test for ensuring retention on the seed. “Rub-off” and “friability” or other similar tests are used and methods vary greatly from company to company.

Verifying that the treatment can be applied uniformly and accurately is of fundamental importance.  Uniformity can be assessed visually with reasonable accuracy by an experienced professional for preliminary work, but results may be deceptive. Developers and those involved in treating process optimization are encouraged to perform seed-by-seed analysis of the loading for objective and reliable verification.

“Coverage” is a related test, namely how uniformly coated the surface of each seed is. This test can be a critical performance parameter for contact fungicides and is important for providing a professional and high value look to the seed.  

Appearance is another factor that defines perceived value. Uniformity and coverage are considerations, but how dark do you want the colouration? How glossy? What shade? These are all commercial questions that require team input and approval.

Performance-driven properties include seed flow and plantabililty. Treatments may hinder or improve flow through a planter, so you need good formulations to deliver performance. Measuring seed flow can be as simple as measuring flow through a funnel or more elaborate such as measuring accuracy through a precision planter simulator. Again, it’s not just one standard test but it should be measured across seed types (for example, flats versus rounds), seed sizes, environmental conditions (especially under high humidity), and other factors relevant to the specific development project. 

Conclusion

Over a career that has spanned four decades, I have seen the seed treatment industry make tremendous gains in the value that seed treatments deliver to the grower and society; and in the quality of treated seeds.  What began with a range of primarily fungicides and perhaps a contact insecticide has evolved into the delivery of many types of agronomic benefits such as nematode control, biostimulants, microbes providing a wide range of benefits, micronutrients, plant growth regulators and many others - with more advances in progress. In addition, modern seed treatments can deliver physical improvements such as better plantability.  These advances were made possible by the evolution of seed treatment formulations, and these advanced formulations require expertise and specialised testing. The importance of these validation steps should be acknowledged by anyone considering bringing a seed treatment to market.

Seed treatment testing is a broad and complex discipline, and doing it well is critical to success. Make sure your organization has access to the right skills and technology, and that you invest appropriately to conduct thorough assessments. It will make a huge difference to your commercial success - and for the stewardship of your seed treatment products and treated seed.  

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This article was initially published in AgroPages' '2021 Seed Treatment Special' magazine.