Often during the season conversations with colleagues drift into discussion about how this year does not compare much to last and how difficult it has been. We always reminisce about that mythical perfect growing season which we seem to remember years ago, when it was warm but not hot, just wet enough and life was easy. I’m not sure it ever really existed but these last two seasons are about as different as they could be.
The 2014 season was warm and wet and brought with it huge canopies plus huge blight and alternaria pressure. This year so far has been very dry, started cold and then became hot, which is translating generally in to crops with smaller canopies and quite different agronomic pressures.
In many non-irrigated fields canopy growth is really struggling, with crops coming into flower when they have only 50-75% ground cover. These canopies are unlikely to expand too much more post-flowering, and there could be significant issues with early senescence if we don’t get some rain soon.
Early senescence can cause various problems – not only in terms of overall yield but also different tuber quality issues such as bruising and black dot – so we must be mindful of these when planning harvesting decisions.
In contrast, some of the fully-irrigated crops have canopies as large as I’ve ever seen, with good tuber size and numbers already showing in the digs. These crops are racing on and will need careful monitoring, to ensure they don’t go oversize and develop growth cracks or hollow heart, as can be the case with such rapid growth rates.
The aphid explosion is also interesting. Whether it’s due to a slow cold start with the hatch being concentrated I’m not sure, but in the last few weeks the aphid pressure has gone sky high, but only with certain species. The pressure has been so different to the last few seasons. Cereal aphids seem few and far between but carrot willow aphid, black bean aphid and now peach potato aphid are everywhere. We know peach potato aphids are resistant to pirimicarb and pyrethroids, so we must use alternative chemistry where these are a known problem.
In all but a few ware varieties – such as Nadine which suffers from PvNty and some processing varieties which can get sugar spot – we’re looking to control the aphids to prevent feeding damage and stop the removal of nutrients and water from the crop. It’s very different in seed crops however, where virus control is the main objective. Anyone who plans to ’home save’ seed could be under more pressure than normal this season, so testing for virus in those tubers is even more important than normal.
Blight is noticeable by its absence with little activity on the Fight Against Blight website. Virtually no Smith Periods are being recorded and I’m seeing hardly any red warnings on my Forecast Extra blight prediction emails. There is a theory irrigation can increase blight pressure, so why aren’t we seeing more blight in these fully irrigated crops?
With transpiration rates running at up to 5mm per day and crops having water applied every five-six days you would think they should be conducive to blight infection. If we look at the blight models they suggest irrigation can have an effect, but only if it increases the leaf wetness of a near miss infection period and turns it into a hit.
In reality, canopies are drying out quickly, even under the most intense irrigation regime. The current weather conditions of warm, dry and breezy enhance this, so irrigation is having little impact on blight pressure. Also, with the lack of any significant numbers of spores flying around, the odd ones which may be getting into a crop are quickly desiccated in the sun. In blight research trials, to get disease pressure going, plots are inoculated with spores and then constantly misted to get the spores to infect new growth, but even that is proving difficult in the current weather conditions.
Things can change quickly with the changeable UK climate (often when attention is drawn to such things) so as cereal harvests get closer potato growers must remain vigilant and react accordingly.
No doubt next year the conversation will again drift to that perfect season we all remember, but back then the snow was always deeper too if memory serves.