Bridging the gap between applied science and farming practice is something CPM is really passionate about. It’s one of the reasons the AHDB strategic potato (SPot) farms are always an interesting visit. But for me the SPot in Shrops is more worthwhile than most. It’s not impressive, it has a massive problem with PCN.
The egg counts are eye watering and I’m not entirely sure how I feel about growing potatoes in this level of infestation. It goes against all my agronomy principles, but then there’s no way of knowing the commercial pressures behind the decision to plant in potatoes, and the farm manager realises he has a far from ideal situation to contend with and is doing the best he can in an unenviable situation. What the site does provide is a fascinating insight in the tolerance some varieties have to PCN and a realisation that not all varietal resistance is the same.
One chance remark on the way round the plots really got me thinking. Someone suggested that in a low egg count situation, they’d be happy to plant a resistant variety without a nematicide. Now I could see the sense in that if a variety was resistant to every single strain of PCN but the reality is they’re not – the likelihood is that you’ll still get some multiplication occurring, especially when in a Globodera pallida situation.
I wonder whether the dependence on rented ground is behind this short-term vision, but then many potato growers are in a long-term situation with their landlords so this shouldn’t be the case. It begs the question, who is responsible for the PCN health of rented ground – landowner or tenant – and is this something that’s even discussed. It’s an interesting one.
The problem when a variety with partial resistance is grown, is the PCN population exposed to selects for increased virulence towards the resistance of the variety in the ground. Work in Northern Ireland has shown that populations of G. pallida can select for 100% virulence to a resistant variety within 10 generations.
Nematicides aren’t 100% effective either, especially against G. pallida which hatches later than G. rostochiensis. But as a part of an integrated strategy, resistant variety and nematicide, surely the goal of reducing multiplication is more likely to be achieved and the extra cost of the nematicide offset by keeping PCN at a more sustainable level?
Integrated pest management is supposed to be central to farming practices, with the idea that the control is greater than the sum of its parts. Using one strategy alone can come a cropper, resistance can break down because the genetic variability in a PCN population can be large, especially with G.pallida.
I vividly remember listening to the renowned nematologist David Trudgill talk about PCN and I’m sure he’d be turning in his grave at the thought of relying on a potato plant’s resistance alone. He believed that populations of 1 egg/g justified a nematicide treatment to keep levels of multiplication as low as possible. And no doubt he was right.
The new nematicides on the horizon look exciting alternatives or additions to the chemistry we currently have available. Certis have NemGuard, a garlic-extract which growers have been using successfully on free-living nematodes in carrot crops. It already has a potato approval but Certis are sensibly building up a knowledge base in the potato crop before a commercial release. The bias that exists towards naturally derived chemistry is an interesting one. I’m sure that if the Certis product was from an established group of chemistry, there wouldn’t be such a need to build grower confidence.
The power of plants shouldn’t be underestimated. Humans have been using them therapeutically for millennia. Plants have their own defence and signalling mechanisms to keep predators at bay and harnessing some of these seems a natural progression in plant protection chemistry. Natural doesn’t mean New Age and ‘fluffy’, indeed some of nature’s chemistry is ferocious.
The Bayer product could also be a game-changer, a liquid application at a low rate of use. Both would be more operator and environment-friendly than the organo-phosphate and carbamate currently available, which has to be a consideration as we move into a new farming era.
