Potato Review

30 POTATO REVIEW MARCH/APRIL 2020 FARM TRIALS “One of the important secrets to getting timely and effective desiccation is to make sure the applied N rates are correct, and on these crops the levels varied, but at Spot North the N applied has reduced following results from trials over the last two years.” Skinset Skinset, which determines harvest readiness, was also assessed using a skinning barrel. Graham said not defoliating slows skinset, but the effects are not always seen immediately. When assessed at three weeks post T1 across all sites, Spotlight/Gozai combinations were less skinset than Reglone, flail or Saltex. In reality, Spotlight and Gozai were two or three days slower in setting skins adequately for harvesting than Reglone, but there was variation across sites. Georgina and Maris Piper were fully skinset at two weeks on two of the sites, whereas Jelly seed, Scottish crops and the Royal crop at Elveden took three to four weeks. “No differences in vascular browning or stem end necrosis were detected across the different desiccation methods,” he said. Stolon detachment was not shown to be a problem in Jelly, Piper or Georgina but there were some cases of adhesion in Royal. “There was less attachment in undefoliated crops, and virtually no stolon plug removal was observed in any of the crops.” Anecdotal evidence suggests that ‘passive bulking’ takes place following application of slower-acting foliar desiccants compared with complete removal of haulm by flailing. However, the average yield loss compared with allowing the crops to grow on was 8-10 t/ha for Reglone, flail, Saltex, Spotlight and Gozai, suggesting that bulking ceased quickly and similarly across these treatments. The yield loss with pelargonic acid was smaller (c. 5 t/ha) and this would reflect the slower leaf kill with this chemical. Potential alternatives As hand haulm pulling was successful, there may be a future for machine haulm pulling, said Graham. However, he noted, ridges would have to match the machinery, which might be quite difficult to achieve. Nevertheless this method could have potential for high grade seed as it is likely to reduce the risk of black dot and blackleg. The performance of some desiccants may be poorer when conditions become cooler and with lower levels of solar radiation, he added. “Some non-replicated plot comparisons in October indicated applications of PPOs later in the day reduced performance. Nevertheless, some of the combinations looked to show some promise.” Another alternative to going over the land with a heavy flailing machine could be thermal desiccation. It still involves driving over the land but the equipment is much lighter. Costs are approximately £105/ha, and it may also require application of a PPO. Protocols for desiccation trials • Targeting vigorous canopies close to commercial desiccation timings • N fertiliser determined by RB209 • Same nozzle type for spray applications • Desiccant rates 400l/ha (except Saltex) • 3-bar pressure • 3.6m spray width • Middle rows targeted in 4-6 row plots Follow-up on Saltex Will Gagg said Saltex performed better than he had expected. “It was efficient, is readily available and has limited effects on the next crop. This is an area we want to follow up next year.” However, others were disappointing, such as pelargonic acid. Expectations had been high on observing differences in the haulms within just 20 minutes of application. However, desiccation did not then go any further down the plant. Irrigation trials Research on the farm has explored different irrigation methods. Will Gagg divided one 10ha field into three parts, all of which were planted the same day. Boom, trickle and rain gun were assessed for efficacy and cost- effectiveness. Two weeks after planting the trickle infrastructure was laid down by irrigation specialist Anthony Hopkins of Wroot Water. The same water was used from the underground main for the boom and the trickle,. Heavy rain in June meant scab control was done naturally and there was no significant difference in yields. But potatoes in the trickle regime were more uniform in size at lifting and could have gone for four or five days more, which would have made a difference in yields,. “We observed a slight better shape from trickle, but there was no difference in bruising. There was, however, a big difference in water usage. Trickle used a mere 1,500 cubic metres, while the gun used 9,720 and the boom 7, 516.” Drip needed less energy, said Will. “With the gun and the boom we had sensors in each section, but with the trickle, we kept it running for six days a week at 2.5mm/day.” He believes that if it had been dry for lifting he may have got a better crop. This year will look at the relationship between irrigation methods and canopy, while recording labour costs and timing. “We observed a slight better shape from trickle, but there was no difference in bruising. There was, however, a big difference in water usage. Trickle used a mere 1,500 cubic metres, while the gun used 9,720 and the boom 7, 516.”