Potato Review

www.potatoreview.com POTATO REVIEW JULY/AUGUST 2022 25 HAULM DESTRUCTION it is easier to target the nozzle to hit little stalks rather than big foliage.” In such conditions effective blight control remains critical, and there is a chance that blight remains a threat until the crop is completely dead, he says. On such occasions, he opts for a tank mix of Ranman (Cyazofamid), Gozai and oil. “This is an approved mix and it works well because Ranman has a good wetting system.” He said other blight sprays offering tuber blight control, such as Infinito, do not have approved tank mixes. Set-up of tractor and flail ‘critical’ to effective haulm destruction The importance of machinery set-up is often overlooked, says Andrew. The flail should be set to cut between 15 and 20cm above the ridge top, and blades need to be sharp. “We quite often see people going too fast and too low with blunt blades, which you can then see on the haulm. It’s very important to go sufficiently slowly to give the flail time to work, and when done correctly the haulm should go to the bottom of the furrow.” Andrew notes that when crops have been sprayed before flailing, the work rate can be increased a little because the haulm is less lush and less bulky. Spray before flailing, flail then spray – assessing the benefits and challenges of the different sequences Choice between the different sequences depends to a certain extent on prevailing weather and crop conditions. While trials have shown it is possible to desiccate using just chemistry, most growers are also choosing to flail as well. “If you are worried about black-leg or an outbreak of late blight, it is a good idea to spray before flailing, as flailing can spread pathogens around. Trial work has shown that if you spray before flailing, stolon detachment is better because it is a more natural process, but it comes at a input higher cost.” The spray rate for Gozai or Albis is 0.8l/ha for both pre- and post-flailing; while Spotlight should be applied at 1.4l/ha followed by 0.6l/ha. Thorough checking to see the crop is dying off is crucial, he insists, noting that any greening regrowth starts in the nodes at the base of the stem. If insufficient water volumes were used, or tractors were driven too fast, not enough desiccant may have landed on the haulm, and the crop may need another application. “Even if you flail before spraying, you still need to maintain the high water volume as the desiccant only kills what it touches. Sometimes two stem desiccations are necessary, so you need to check your maximum applications for the product you use. For example if you applied Gozai at 0.4l/ha as you as a herbicide, because it has a maximum per season of 1.6l/ ha, you will have to look at Spotlight for the second desiccation spray.” The permitted spray total for Spotlight is also 1.6l/ha, so the same would apply if it had been was applied earlier as a herbicide as well. He reminds growers that if they change desiccant, they need to keep in mind that Spotlight has a seven-day harvest interval, while for Gozai it is 14 days. He is not an advocate for flailing and spraying to be done at the same time, because the flail creates wind vortexes which often mean that accurate application of the spray is harder. A lot of crop residue is also left on top of the ridge, making stem contact by the spray more difficult. “Once you have finished flailing, you should leave the crop between 24 and “If skinset is not right, you can lose more revenue than the extra tonne per hectare that you got from waiting for too long to lift and then not taking the time to leave the crop for a month to desiccate properly, opening the door to infections and rots.” 48 hours before going in with a stem desiccant to give time for the haulm at the top of the ridge time to dry off.” Skinset or total yield – which has the bigger effect on the bottom line? One of the industry’s biggest areas for discussion is how to increase yields, and many want an extra tonne per hectare, but what is most important is the revenue collected from selling the crop, says Andrew. “If skinset is not right, you can lose more revenue than the extra tonne per hectare that you got from waiting for too long to lift and then not taking the time to leave the crop for a month to desiccate properly, opening the door to infections and rots.” TRIALS ON DESICCANTS AND NOVEL METHODS OF HAULM DESTRUCTION Spotlight and/or Gozai straights when they are used in combination with flailing, give the quickest desiccation results, says Andrew. “We have looked at alternatives in trials but there is nothing suitable at present.” Andrew Goodinson