Potato crop harvest management requires a different approach to the challenges faced by Patrick Levinge of Velcourt when he started out as an agronomist some 25 years ago.
Mr Levinge advises growers across 450ha of potatoes. With customers in South Yorkshire, Herefordshire, Worcestershire and Gloucestershire, he encounters different soil types, varieties, temperatures and other factors affecting haulm desiccation.
“It’s fair to say that more advanced planning is involved now,” says Mr Levinge. “Given the loss of actives over the last 25 years, there are also significantly fewer chemical options for growers.”
When the diquat ban took full effect in 2019, Mr Levinge says he decided to adjust his end of season crop burn-down planning by a further 14 days to take into consideration the additional time he felt was needed to desiccate without diquat.
Trust the system
“What I’ve learnt since, is that it takes roughly the same amount of time for complete desiccation, stolon detachment and skin-set using a flail and spray approach.” he says.
“The difficulty is that during the process, unlike with diquat, you don’t get the obvious early visual signs in the crop, so it’s all about confidence and trusting the chemistry and the system.
Chemical alternatives still exist in the form of a group of herbicides called PPO inhibitors. Mr Levinge says his go-to PPO inhibitor is Gozai (pyraflufen-ethyl). It’s been with us since 2016 and can also be used in early season weed control.
“It has an excellent crop safety record with no detectable crop residues or adverse tuber effects. When desiccating you must be decisive – particularly when tuber sizes have been achieved and warm, dry weather conditions are forecasted.
“As I’ve normally already used Gozai at 0.4l/ha earlier in the season, my key strategy is to go into the crop with an initial application of Gozai at 0.8l/ha, with methylated seed oil (MSO), to open up the crop creating a ‘false’ senescence.”
Mr Levinge adds: “Then we flail, ensuring complete separation of foliage and leaving fully exposed stems to give the second application of carfentrazone the best opportunity to attack the severed stems.”
For ongoing tuber protection, Mr Levinge would add Ranman Top (cyazofamid) to the tankmix in the first and second sprays. As with all PPOs, Gozai doesn’t travel through the crop, so the key is applying it in water volumes of at least 300l/ha to ensure coverage.
“To maximise Gozai’s efficacy, you must always try to apply it in bright, sunny conditions – ideally between 10am and mid-afternoon when the sun is at its hottest.”
Although there are many factors to consider when desiccating, the keys are crop nutrition when managing canopy size, soil type and the variety being grown – whether determinate or indeterminate.
Irrigation can be useful when managing canopy size and encouraging senescence before flailing. The key on canopy management is to feed just enough nitrogen but avoid total haulm collapse which could then lead to poor flailing, inhibiting the PPO.
“As his customer base is 100% flail and spray, Mr Levinge rarely advises a chemical-only desiccation strategy. Although readily achievable – particularly when dealing with determinate varieties that naturally senesce, using chemicals only is less economical.
“It will take longer to achieve a successful outcome than a flail and spray approach – particularly when weather conditions aren’t consistently favourable for applying multiple PPOs over a longer time period at 7-day intervals.”