Take a more flexible approach to potato desiccation when the weather isn’t always right
A Scottish agronomist responds to the challenges of desiccating potato haulm in the North East Highlands.
Advising 500 ha of potatoes each year in Moray, Inverness-shire, Black Isle and Easter Ross, Agrii agronomist Ed Scaman is quick to recognize the unique challenges he faces each season when working with potato growers based in the north of Scotland, where windows of sustained dry weather are both rare and often difficult to predict.
“Of course, adverse weather conditions and soil temperatures dictate all areas of potato production, from planting dates to weed and blight control. But, at the end of the growing season, crop desiccation – in particular, can be the most difficult challenge when strategy planning is based on establishing a dry weather window,” explained Ed.
“Colder early season soil temperatures and shorter summers mean we plant later and tend to harvest much earlier and it is this compressed season that dictates every aspect of crop management.
“Adverse weather early in the season can often cause a wide variation in emergence times and, due to our summer humidity combined with generally higher rainfall, late blight (Phytophthora Infestans) and desiccation pose significant challenges” , he added.
“In 2018, we fully committed to a flail and spray approach, advising customers to adopt a new desiccation approach before the diquat safety net is removed. Looking back, I think it was the right strategy, giving us time to assess the merits of the leading PPO inhibitors carfentrazone and Gozai (pyraflufen-ethyl). »
He further explained that critical factors for successful desiccation must include a flail well to ensure clear separation of stems and foliage. Stems should be 15-25cm in length and PPOs should be applied in the morning – ideally in bright, sunny conditions to maximize their effectiveness.
“If an indeterminate variety is grown, it is advisable to apply a PPO pre-flail to create a ‘false’ senescence in the crop. However, with an indeterminate variety you are more likely to get a natural stop on the canopy pruning allowing you to look for a window of dry weather to wither and then apply the first PPO Given our shorter season I usually start telling customers about the onset of desiccation in late August – being given that the weather and temperatures can often deteriorate rapidly in September.
“However, the optimal weather conditions for desiccation in my territory are rare – if a crop has started to age, I will continue to actively search for a 3-4 day window of dry weather. Starting with 1l/ha of carfentrazone to open the crop, we then apply Gozai at its full rate of 0.8l/ha with methylated seed oil (MSO) alongside an application of Ranman Top (cyazofamid) to give the culture a continuous effect. protection against tuber blight by desiccation while killing any zoospores remaining after the blight.
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“To ensure good product coverage, I would always recommend applying Gozai in water volumes of at least 300 l/ha and ensuring that the PPO is applied no later than 48-72 hours after the culture was beaten,” said Ed.
“On seed crops, once the tubers have reached their target size, you need to be decisive and if the dry weather window is there, first enter the crop with a PPO to create this ‘false’ senescence before whipping and then applying up to 2 sprays of Gozai at 0.8l/ha per post-blight application.
“Seed crops can be very tricky, given that they want to keep growing, so the key is to follow the first application of Gozai quickly after the blight to minimize the potential problem of stem regrowth and killing the crop before any other diseases can take hold in the crop,” he added.
“Due to our geographic location and weather conditions, I rarely recommend a chemical-only desiccation strategy to a customer. However, if the client cannot wither – and if a certain variety is being grown and has naturally started to age, I would generally advise 2 applications of Gozai at 0.8 l/ha + MSO followed by an application of carfentrazone at 1, 0 l/ha at 7 day spray intervals until crop has dried out.
“Growers should keep in mind that a chemical-only strategy is less economical and will take longer to achieve a positive result than a flail and spray approach,” Ed concluded.