Potato Review

www.potatoreview.com POTATO REVIEW JULY/AUGUST 2022 23 HAULM DESTRUCTION crop, it is well worth ensuring that you finish the job well, and that means getting your haulm destruction right,” he said. Well-planned haulm destruction starts well before planting, and one of the critical areas is nitrogen management, which needs to be decided according to determinacy. Determinacy is the measure of a plants capacity to maintain leaf production after first flowers. Most main crop varieties are in Group 2 with medium haulm longevity (partially determinate) or group 3 long haulm longevity, (indeterminate), Andrew explained. Varietal determinacy also plays a key role because of its influence on haulm size and vigour. For example, indeterminate varieties such as Markies and Maris Piper not only grow a lot of haulm, but it is also very long lasting. He notes that long haulm varieties tend to have slightly less total N applied. Semi-determinate varieties start so senesce sooner. Melody, which is a semi- determinate pre-pack variety, still has a bulky canopy, while crisping variety Lady Claire grows smaller canopies with less bulk, so there is a different amount of haulm. Later-maturing indeterminate varieties can be more difficult to flail effectively to an even length, as often the haulm has dropped down into the valleys between the beds, which the topper blades struggle to reach, he adds. While physiological seed age can affect when potato crops start to senesce it is difficult to assess because most seed potatoes are purchased as a commodity, and Andrew points out that many growers do not have any control over this. Andrew added that many growers have been considering reducing their N applications, so that the crop starts to senesce earlier. “If organic manures have been applied and the season has been dry early and wetter later (or irrigated) the plant uptake of N can continue over a longer period and canopies continue to grow,” he said. “This can affect dry matter content levels at harvest, and make crops more susceptible to bruising. “It is easy to say that you have to cut back on N applications, but in reality you have to look at the whole picture because you want optimum uptake of any applied N, which relies on having the right balance of potash and magnesium. Together they affect N uptake efficiency as well as the bulk, vigour and lushness of the canopy.” Other considerations include whether the crop will be harvested green-top or is destined to be a seed crop (which is usually desiccated when the haulm is still very green). In addition, the time the crop is expected to be in storage needs to be taken into account, as many are stored until June/July. “Storage requirements are a critical element; crops destined for long-term storage, which are often stored until May or June, need to go into store in the best conditions possible. For example, the crisping variety Lady Claire can be temperamental to grow, but it is quite easy to stop and it dies off quite quickly. One of its important traits is its storability; as long as you take the necessary four or five weeks to ensure the plant has properly died off and to achieve a good skinset, it stores really well.” It is a also good idea to consider field layout and soil type, says Andrew. “When planning, take note of any rented fields which need to be vacated by a certain date and look at “It is easy to say that you have to cut back on N applications, but in reality you have to look at the whole picture because you want optimum uptake of any applied N.” ➜ Since the withdrawal of diquat and the extra time now needed to ensure the crop is completely dead, some growers have preferred to bring their harvesting dates forward.