Potato haulm destruction: desiccation and flailing

Desiccation and the loss of diquat

Haulm destruction in potatoes can be achieved by mechanical or chemical methods or using a combination of the two. Until its withdrawal in 2019, diquat was widely used for desiccation. Its loss has made haulm destruction a potentially more difficult and unpredictable process, especially in  actively growing seed and salad crops and with indeterminate varieties in a wet autumn. 

Factors to consider regarding haulm destruction are summarised below. More detailed articles on the SPot Farm results are also available.

What to consider before you plant

Bed formation and machinery set-up

If considering a combined mechanical and spray approach, check bed formation against the flail set-up. Destoners and planters operate on a single bed, but flails may operate over two or three beds, so it’s important to match the topper to the rows.

Field layout

Leave enough space to turn a flail at the edges of fields. This may mean not planting the headland.

Nitrogen rates

Review nitrogen rates to try to keep haulm to a minimum and avoid over-vigorous crops at the time of haulm destruction. See RB209 recommendations for potato crops. Indeterminate varieties will require particular care when it comes to nitrogen rates and desiccation. Results from on-farm trials in 2020, suggest that in crops which have difficulty in achieving skin set owing to active green canopies at desiccation, 10 % less nitrogen than the RB209 amount should be tested to try and advance canopy senescence.

Variety choice

While there is often limited variety choice for growers, knowing your cultivar (e.g. its determinacy rating) is important. Consider haulm destruction when deciding what variety to plant where. Some soils will not bear the weight of a flail well under wet conditions. Such land is better planted with varieties that are easier to finish, with the difficult varieties allocated to drier more resilient fields.

AHDB SPot Farm trials in 2019 and 2020 compared chemical desiccants and flail-and-spray approaches. The work assessed different sequences of protoporphyrinogen oxidase (PPO) inhibitors [pyraflufen-ethyl, carfentrazone-ethyl] and compared them with undefoliated control treatments.  The desiccants were also combined with flailing and in 2019 diquat was included for comparison. Some experimental chemical treatments were assessed in both years. 

The trials included vigorous, complete canopies at close to commercial defoliation timings and assessed the speed of leaf and stem desiccation, skin set, and effects on yields and internal defects on both ware and seed crops.  The cost of the different approaches was compared in 2019.

The detailed results and discussion are provided in the research reports.

Practical recommendations from the trials

• Quick canopy kill does not necessarily mean quick skinset

• Aim to apply PPO desiccants early to mid-morning, ideally on a sunny day

• Wet soils mean slower skin set, so stop irrigation 7 days before desiccation

• Expect a one to four day delay to skinset when using alternatives to diquat

• Slower canopy death means you will need to manage disease risk until all 'green material' is gone

The results presentation begins at 7:24 and lasts for approximately 50 minutes