Late planting may bring extra challenges – Potato Review
Andrew Goodinson says now is a good time for planning for the 2023 harvest, thinking through preparations in the field and the impact of nutrition strategies ...
This year, given the late planting most growers are having to contend with, lower N application rates may be necessary because the crop will still need to senesce at the same time.
Although savings of 30-40 kg N/ha could be possible, achieving them may be complicated because of the need to use N to keep foliage green and reduce stress and infections such as Alternaria, so growers may still opt to apply a top dressing with 40 kg N as a liquid methylated urea product.
Closing up seed rates may be advisable, because later planting can mean seed sets fewer tubers so potentially giving a lower yield as well as a lower tuber count which can be important especially in crisping potatoes.
Although physiological seed age can affect when potato crops mature and start to senesce, many growers do not have access to this information because most seed potatoes are purchased as a commodity, Andrew says.
As determinate varieties have short haulm longevity, chemical desiccants such as Gozai (pyraflufen-ethyl) or Spotlight (carfentrazone-ethyl) work well work to open up the crop and start the senescence process.
When the variety is determinate and already senescing, if the first application of a desiccant opens it up sufficiently, a second desiccant may be applied after seven days and flailing may not be necessary, he said.
However, indeterminate varieties continue growing, and as they do not start to senesce by themselves, they need managing to stop leaf and haulm stem growth prior to harvesting and kick-start skinset.
Some varieties, such as Markies and Royal, can have a lot of green foliage to remove, particularly when they have been grown on fertile soils and if the stolon attachment is still too strong at lifting it can result in mechanical damage and bruising.
Moreover, when the crop is a later maturing variety, it can be more difficult to flail effectively to an even length because the haulm can be lying down into the furrow, making it difficult for the topper blades to reach, he adds.
“This highlights the importance of applying a pre-flail spray with Gozai and/or Spotlight in a mix with Ranman (cyazofamid), to prevent tuber blight. We always like to carefully check the crop to make sure it is dying off and there is no regrowth at the base of the stem,” said Andrew.
“If the operator did not use sufficient water volumes, or perhaps was a little fast through the field, the crop may need another application of desiccant, always making sure maximum application rates have not been exceeded.
“It is important to keep water rates between 300 – 400l/ha for the applications to work well and trigger senescence – opting for forward and back facing nozzles is a good idea for the best results.”
For indeterminate varieties, 400l/ha of water remains more appropriate, he notes, emphasising that the amount of active ingredient (ai) remains the same, it is just the amount of water which changes.
“The optimum time for dessicant application is between late morning and late afternoon on a sunny day. Of course this is not always possible, and if conditions are dull they still work but timings tend to be slower.”
Desiccation normally takes around seven days and is then followed by flailing, and then another application of the desiccant targeting the stalks and prevent further growth.
“Flails should be set up leave about 8in (20cm) of stem which facilitate uptake the second application of a desiccant. The machinery should also move the flailed haulm off tops of ridges and into the furrows so the spray hits the stems more effectively.”
Really vigorous crops may need up to three applications of a desiccant, he adds, warning that care must be taken to ensure that maximum dosage per crop hectare (ha) is not exceeded throughout the season.
“For example, if you are using Spotlight Plus for desiccation you have to comply with a 1.0l/ha maximum individual dose, with a maximum total dose of 1.6l/ha.”
If Gozai is being used, any applications which were applied for weed control need to be included as part of the allowed total dose, which may mean a reduction in rates for repeat treatments for desiccation. It is important to ensure desiccation is done well because we can get regrowth from the base of the haulm in most seasons, which is usually due to variety or poor application and/or coverage.”
Good training of staff can make a real difference to final results, he says, noting that if they are new to the job, understanding the consequences of moving away from best practice can help keep them on track.
“It is important that the tractor and harvester do not damage the ridges before lifting from them,” said Andrew, noting that some growers choose to windrow, lifting and placing tubers onto another bed to help skinset and curing. However, he adds, if not done carefully, the extra handling can cause more damage.
Ensuring operators know the implications of bruised tubers and mechanical damage and how they can develop into rots once they instore, is also important. If dry matter levels are high, tubers may be susceptible to broken skin surface which can open the door to pathogens such as fusarium and wet rots, so extra care may be needed, particularly when harvesting temperatures are high.
“It is important to keep water rates between 300 – 400l/ha for the applications to work well and trigger senescence – opting for forward and back facing nozzles is a good idea for the best results.”
“Losses from bruising can cost the grower £200/ha, so ensuring they know how to take samples from different stages of the harvesting process to determine where damage is being done.
“For example if the damage is being done at the top of the harvester web, adjustments may need to be made there, but this would not help if it is occurring on the haul separator.”
Now is a good time to review hardware, and whether it needs repairing or improvements, and taking time to train new operators, says Andrew.
Tubers damaged during harvest can soon make a dent in profit margins, he stressed.
“Prior to starting harvest, it is always a good idea to check equipment such as the flail, making sure that the blades are sharp, and the flail should be set to cut between 15 and 20cm above the ridge top, and the haulm should fall to the bottom of the furrow. If they are worn out, or the operator is going too fast you can an uneven chop and stolon end damage on potatoes,” he says.
Checking grader belts to ensure no tears or excessive drops, as well as ensuring potato boxes are in good order, can also help keep harvesting on track.
He also recommends revising machinery for sharp points, and any roller damage which may resulting in pinching or slicing. In addition, correct setting of the share height ensuring haulm rollers are not set too aggressively can help minimise damage.
“Understanding the variety being harvested also helps the harvester operator assess how deep the discs should go. This is because some varieties set the daughter tubers around the mother while others are set below.”
Bruising can also cause losses, so he recommends minimising drop heights and where possible using mats or cushions to keep handling as gentle as possible.
Keeping a close eye on tubers can help identify problems which can be dealt with in a timely manner, so he advises taking samples taken at different steps of harvesting process at different times throughout the day. These should then be hot boxed for twelve hours at between 32 -34 deg°C.
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