Previously, grain diseases transmitted by seed were controlled with synthetic-chemical seed dressings. However, if seed is healthy, no treatment is necessary. As the demand for pesticide-free grain increases, professional seed inspection is gaining importance.
Seed-borne pathogens have major global implications. In Switzerland, snow mould, common and dwarf bunt, leaf and glume blotch as well as loose smut are the main seed-borne cereal diseases. In the past, synthetic-chemical seed dressings were very effective in preventing their spread.
A large proportion of certified grain seed in Switzerland is still treated with chemical seed dressings, resulting in an annual application of around 50 tonnes of plant protection products (PPPs). The national Plant Protection Product Action Plan also highlighted the demand for untreated or organically dressed seed. Although organic seed treatments are only available to a limited extent in Switzerland, Cerall®/Cedomon® (bacterial compound), Tillecur® (yellow mustard flour) or a steam treatment (ThermoSem®) are available.
Lower use of seed dressings thanks to seed health tests and damage thresholds
Seed health tests and the application of damage thresholds are an important tool in addition to seed treatments: If, for example, less than 10% of the wheat kernels are infected with snow mould, a seed dressing is not needed. Agroscope developed these thresholds for the main cereal diseases and has applied them consistently to organic seed since the 1990s. The number of samples examined per year rose from 120 in 2011 to 341 in 2020 (Fig. 1). Over the past two years, seed for IP-Suisse pesticide-free production has also been inspected.
A seed lot with minimum germination levels and below the damage threshold for all test items is considered healthy. In most years between 2011 and 2020, over 80% of the seed samples inspected were healthy, and could be recommended for untreated sowing. Thus, it was possible to sow untreated seed whilst deliberately reducing chemical seed dressings. For loose smut, the examination is performed during a field inspection as part of the seed certification, since laboratory testing is currently too laborious.
The weather has an impact on the occurrence of seedborne diseases in cereals
The percentage of healthy grain seed varied significantly depending on the weather. Only in three of the last ten years – 2011, 2012 and 2016 –the quality was too low, due primarily to the humid weather, which led to increased snow mould infection. Over the last ten years, the cultivation of less-susceptible varieties has removed leaf and glume blotch from the picture; consequently, it has not been tested for since 2019.
Thanks to consistent seed health tests since the late 1990s, the occurrence of common and dwarf bunt infections were reduced and subsequently maintained at a very low level. In the case of barley, loose smut infection occurred more frequently during the field inspection, even with chemically dressed seed lots. Agroscope is currently developing a molecular method for quantitatively detecting the disease in the seed as an additional tool for faster and simpler identification of the pathogen.
- Since more and more seed producers are switching to pesticide-free production, it is important to examine seed health.
- There has been a significant increase in the number of seed lots considered to be healthy and which could thus be sown untreated. Both the weather conditions and consistent seed health inspection played a key role.
- The range of effective seed dressings approved for use in organic production is currently very limited. It is therefore important to use healthy seed and to breed for less susceptible varieties.
- Modern, efficient methods for testing seed health are of crucial importance. Agroscope is currently developing a molecular method to detect loose smut in barley seed, since this disease cannot yet be efficiently quantified with classical methods.