What does this photograph tell us about root exudates and black-grass?

As an agronomist walking fields of winter cereals I began to notice patterns, none more so than highlighted in this photograph showing a field drilled on the right and then the drill bridged with seed. The grower was unable to return and plant the rest of the field. The peri-emergence herbicide was applied to the crop that was drilled, yet it soon became obvious that where, at the point the drill had become bridged and where no pre-em had been applied, the black-grass was significantly worse.

  • On the right where the crop is drilled and pre-em applied, there was not much black-grass
  • In the centre where the crop is finished to be drilled and no pre-em applied – lots of black-grass
  • On the left where there was no crop drilled and no pre-em, there was not much black-grass.

Were root exudates encouraging the germination of black-grass?

This led me on a learning journey which began on the internet, back to the 1930’s and finished with the ancient Greeks!

I began by trying to study crop effects on weed populations and, despite extensive internet searches, found very little, except the fact that it became obvious that certain weeds were triggered in certain crops. Oilseed rape always promoted the growth of charlock, poppy and sow thistles as well as black-grass and cleavers, yet in wheat very few problems associated with sow thistle ever seemed to show and the other broad leaved weeds to a lesser extent than in wheat, yet black-grass and cleavers seem to be strong in both these crops. The more times you type allelopathy in to an internet search engine, the harder it is to ignore history and without herbicides it soon became obvious that for 4,000 years agriculture managed to feed the world as necessary without transport and storage that we have today. This of course meant that a thorough understanding of plants and their physiology should not go ignored – after all we still use Pythagoras’ theorem today!

On reading much ancient literature it soon became obvious that the relationship between different plant species were interlinked, as one could have a huge effect on the other. Control of black-grass at the time was still relatively straightforward with herbicides still enjoying great results and my theories remained quite humorous amongst my contacts. However I continued some basic trials for years after in the knowledge that resistance was a real issue and there was nothing really in the herbicide pipeline. I was extremely fortunate to be awarded a Nuffield Scholarship in November 2015 to look closer into the non chemical control methods for black-grass and look forward to updating this blog with my journey.