A robust blight strategy more essential than ever as new blight strains continue to evolve

Control strategies for late blight are constantly developing as the pathogen causing the disease evolves and the available blight chemistry changes, either due to regulation or efficacy shifts due to fungicide resistance, according to independent agronomy company Farmacy Plc in the UK.

Overcoming issues such as these is a key part of the Hutchinsons’ blight trials, first set up in 1997, Farmacy reports on its website. These are examining how both new and established fungicide chemistry compares at different stages through the season.

The trials were initially hosted near Holbeach in Lincolnshire, but three years ago moved to a new site within the county, on Grade 1 silty clay loam to the east of Boston.

This year around 30 products will be compared across replicated 6m plots at the 1ha site planted with Melody. The trial is managed specifically to test products individually under higher blight pressure than might otherwise be found in the field.

To maximise disease pressure, the site is surrounded by a maize strip to reduce airflow through the potato crop and increase humidity. Crops are planted late (typically mid-late June) and mist irrigation is applied.

Plants with known blight strains, such as 13_ A2 and 6_A1, are then deliberately introduced early in the season.

“Melody is good for blight trials because it’s a susceptible, bushy, long-lasting variety that goes on growing later in the season,” explains trials co-ordinator Michael Rodger from Richard Austin Agriculture.

“With blight strains constantly changing, it’s important we see how products fare at different stages in the season so our agronomists can give the best possible advice to growers. For these trials we want blight pressure to be as high as it can be to push products, although it’s a very seasonal disease which can still be a struggle to get going in some years,” he explains.

In-season tissue analysis allows agronomists to identify which blight strains and genotypes are present at given points through the year and this improves the understanding of disease development and control, adds Michael.

Notably the past two seasons have seen the 36_A2 blight strain become more dominant, even though the trial was not inoculated with it, he says. It echoes a trend that’s been seen in other blight trials in different parts of the UK.

“36_A2 is more aggressive than 13_A2 or 6_A1 and came in really fast last year, even when there was relatively little rain but just enough humidity. We’ve not seen the 37_A2 fluazinam-resistant strain in these trials yet, but it’s another that has got to be considered when planning strategies.”

Results to date clearly reinforce the importance of monitoring local conditions carefully and being prepared to manage the potential risk with targeted chemistry and tight spray intervals, from planting right through to harvest, he comments.

“It’s essential to establish a clean canopy early on and keep it that way through the season. Blight can never be overlooked, even when crops are on the way out at the end of the season and there may be a temptation to miss out later blight sprays,” he says.

Read the full report on the Farmacy website here.