With planning underway for the 2020 potato season, results from the Hutchinsons Fenland crop demonstration, in Suffolk, have provided a timely reminder of how important careful variety selection is for managing key agronomic challenges.

Variety characteristics are particularly important for potato cyst nematode (PCN) control, which is a focus of the Fenland trials, while other work shows the loss of diquat for desiccation and haulm management could further affect planting decisions.

In terms of PCN, John Keer, of Richard Austin Agriculture, said that although nematicides remain useful, growers should make the most of varietal resistance and tolerance. “Our work over three years shows real inroads can be made into PCN control with judicious use of the most appropriate varieties, and it may be possible to ‘buy’ leeway to grow less resistant varieties in combination.”

This year’s trial site, hosted by AL Lee Farming, was under higher PCN pressure than previous seasons, with an average initial egg count (Pi) of 115 eggs/g of soil, all globodera pallida. Some 18 varieties with different levels of resistance and tolerance were trialled to see how crops performed and how they impacted on the PCN egg count in the soil after harvest (Pf).

Results show a similar pattern to previous years, with Cara performing worst for PCN multiplication, with a Pf:Pi ratio of 4.5. This was despite it doing well in the tolerance trial and shows the clear practical differences between ‘resistance’ and ‘tolerance’.

“Markies also performed badly and has been consistently poor, typically averaging 2.5 to 3-times multiplication in three years of trials,” Dr Keer said.

In contrast, resistant varieties Performer and Arsenal were again most effective at reducing PCN over the season, with a Pf:Pi of less than 0.5 (ie egg count halved). “Performer, Rock and Innovator have shown good consistency for reducing PCN after a crop in our trials. Lugano, Libero, and Royal also did well in 2019,” he said.

Varietal tolerance results generally support previous years, with more vigorous varieties such as Arsenal, Cara, Performer, Rock and Royal, showing good tolerance, while Maris Peer, Innovator and Sagitta were less tolerant. “Markies is the one that seems to break the rules. It’s very vigorous, but shows low tolerance,” he added. “PCN tolerance is heavily dependent on soil type and moisture, as very fertile soils can be more forgiving to the effects of PCN, while dry conditions reduce nematode movement.”

Consider canopy management

With pre-harvest desiccation set to become more difficult and take longer without diquat, agronomist Andrew Cromie said some growers might need to re-evaluate variety choices, cropping plans or fertiliser strategy to reduce the likelihood of having very large, growing canopies late in the season.

The desiccation and haulm management trial shows flailing followed by repeated splits of chemical desiccation will be key to canopy destruction, especially for large, determinate varieties. A herbicide application prior to flailing also helps open the canopy.

Post-emergence herbicide crop safety trial findings:

All post-ems have some potential to cause crop damage, but varieties differ in their response.

Agria has consistently shown more adverse effects from all bentazone-based treatments, whereas Performer and Royal showed fewer effects and grown away well.

Rich, black soils are more resilient than other soil types.

Weather after herbicide application affects the ability of crops to recover from damage.