Variety and end use are the main determinants of which of the widely differing desiccation programmes will be most appropriate for each potato crop.
Given the wide range of crop types being grown such as salad, pre-pack, processing and seed crops, it is not surprising that growers are using widely differing desiccation options. In particular, the loss of sulphuric acid has left growers looking at new options for rapid desiccation when stopping green top crops such as seed or vigorous varieties like Markies, explains Dr Reuben Morris of Frontier Agriculture.
The desiccation demonstration by Frontier at the East of England Potato Day, hosted by Frederick Hiam at Tuddenham, Bury St Edmunds in September compared widely differing options on a vigorous immature crop of Markies.
Dr Morris explains: “The demonstration plots were planted on April 26 and the main desiccant had to be applied on August 17 to be ready for the open day on September 1.”
Treatments and Application Dates
|August 11||August 17||August 25|
|Flail fb carfentrazone-ethyl||Nil||Flail fb 1Lt/ha carfentrazone-ethyl||Nil|
|Carfentrazone-ethyl Sequence||1Lt/ha diquat||1Lt/ha diquat + 1Lt/ha carfentrazone-ethyl||0.6Lt/ha carfentrazone-ethyl|
|Diquat Sequence||1Lt/ha diquat||2Lt/ha diquat||2Lt/ha diquat|
|Single Diquat||Nil||4Lt/ha diquat||Nil|
|Single Glufosinate ammonium||Nil||3Lt/ha glufosinate ammonium||Nil|
Flail fb carfentrazone-ethyl was most successful as it rapidly desiccated the crop and prevented regrowth. The carfentrazone-ethyl sequence provided slower desiccation but was also effective at preventing regrowth. Regrowth scores are given below
Regrowth Scores on September 23
|Untreated||Flail Only||Flail plus carfentrazone-ethyl||carfentrazone-ethyl Sequence||Diquat Sequence||Single Diquat||Single Glufosinate ammonium|
A major advantage of diquat over glufosinate ammonium and carfentrazone-ethyl is speed of activity. To take advantage of this, two doses of 1Lt/ha diquat were included in the carfentrazone-ethyl Sequence. The wetter used in the carfentrazone-ethyl formulation also increases the activity of the diquat, allowing the diquat dose to be kept low.
Regrowth was much less vigorous following carfentrazone than diquat as can be seen below. Prevention of regrowth is a good reason to include carfentrazone in the last desiccant but only once the leaf canopy has been removed either by flailing or with diquat. Glufosinate ammonium cannot be applied until natural senescence has begun or following flailing
Regrowth in the carfentrazone-ethyl Sequence (left) and Diquat Sequence (right)
While difficult to quantify, visual assessment showed stolon detachment was greatly improved by application of all the desiccants, particularly the Flail fb carfentrazone-ethyl, when compared with the untreated. Flail Only had much less impact on stolon detachment when compared with the Flail fb carfentrazone-ethyl showing the effect was largely a result of the desiccant rather than the flailing
Stolon detachment in the Untreated (left), Flail Only (middle) and Flail fb carfentrazone-ethyl (right)
While 4Lt/ha diquat as a single application is a legal recommendation, agronomists avoid recommending it on too vigorous green canopies because it is occasionally associated with browning of the vascular ring in tubers. However, inspection of cut tuber samples from each treatment showed 4Lt/ha diquat had not caused vascular browning in the demonstration. Dry soil around the tubers at application is associated with vascular browning effects and a ‘SMART test’ was passed before application of the desiccants on August 17, indicating enough moisture was present for safe use of diquat.