Every year I get asked the question if a seed treatment is needed for small grains. Invariably my answer is that:
- Yes, if your seedlot carries a seed-born disease like loose smut of wheat.
- Yes, if you have a scabby seedlot.
- Possibly, if you have a known history of wireworms in a field.
- Possibly, if you've been in continuous small grains (>2 years) and you started seeing a higher incidence of root rots like common root rot, Fusarium crown rot or take-all.
In all other situations, seed treatments are much like life insurance; it pays only when disaster strikes during the very early stages of the crop and initial stands are reduced enough that grain yields are reduced because of the lower initial stands that could not be compensated for by additional tillering from adjacent plants.
The three major soilborne fungal diseases that reduce initial stands in Minnesota are Pythium damping-off, common root rot (CRR), and Fusarium crown rot (FCR). While pythium likes cold and wet conditions, common root rot favors cold and dry conditions, and Fusarium crown rot thrives when conditions are warm and dry.
Understand that seed treatments do not provide season-long control. Latent infections of CRR and FCR that do not outright reduce the initial stand or CRR/FCR infections that occur later in the season generally do not become evident until the middle of the grainfill period when affected plants suddenly die back and become these very visible 'whiteheads'.
Andrew Friskop, Extension Plant pathologist at NDSU, analyzed a large number of seed treatment trials across North Dakota to dig a little deeper into what conditions spell disaster such that the initial stands are indeed reduced enough to warrant seed treatments. His summary was just published in the NDSU Crop and Pest Report and can be found here.
In the absence of the criteria listed for using a seed treatment above, seed treatments in this meta-analysis of trials conducted between 2003 and 2021 showed that in about 70% of the trials, seed treatments improved initial stands. Unfortunately, the summary graph does not show how large the difference in initial stands needs to be statistically significant (after all, there was an experimental error in each of those trials that did not allow Andrew to conclude that the increase in the initial stand was due to the seed treatment or luck of the draw) or whether those initial stand improvements actually improved final grain yield. Andrew also looked at the influence of the amount of precipitation in the week prior to seeding and the soil temperature during seeding on the initial stand. Neither wet and cold nor warm and dry or any other combination of the amount of precipitation leading up to seeding and soil temperature during seeding really could explain the improvement in initial stands. The latter makes sense as the three casual agents of initial stand reductions like different conditions.