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Even the best blight programmes have been challenged this season – Darryl Shailes – Arable Farming

A combination of rain and a lack of sunshine over the last few weeks has meant the grass in the garden has been a constant challenge ...

… with continuous growth and very little opportunity to get the mowers out, although it has been interesting to see all the wildlife in the longer grass.

We’ve been able to have people to stay some weekends with the lifting of many of the Covid-19 restrictions, so that’s taken away some of the time available for garden chores and is much more fun than sitting on a lawnmower. It almost seems to be getting back to normal.

Blight control has been a challenge due to the rain. Even the best programmes have been challenged and blight is appearing in many crops. The early reports of genotypes have all been finding that it’s the EU_36_A2 strain which has been causing the problem in East Anglia.

This strain first appeared a couple of years ago and has been dominating the blight population in East Anglia ever since. In our inoculated blight trials, we have always used Blue_13_A2 and Pink_6_A1 and these are generally what we’ve been finding at the end of the season too. However, over the last two years they have been outcompeted by EU_36 A2 and when we’ve tested at the end of the trial, all have come back to show this strain has dominated the trial to the extent that we can’t detect Blue_13_A2 and Pink_6_A1.

Aggressive

It’s not difficult to understand when we look at how aggressive it is. Research has shown that the sporulation is several times more than the others, its spore-to-spore time is reduced and it is able to operate in a broader range of temperature and humidity than the older strains.

Work has also shown that at very low levels of active, some chemistry is challenged. There is no great concern around resistance, but it may indicate that as the gaps increase due to available spraying days or towards the end of the interval between sprays, EU_A2_36 is able to still sporulate and could be a problem.

Programmes need to be tight and contain curative actives whenever the weather is conducive to blight, now more so than ever before with these aggressive new strains.

EU_37_A2, which is resistant to fluazinam, has diminished with the active’s reduced usage, but we must still be aware that changes in practice may bring it back to the fore.

There is also work published to show that other strains are overcoming variety resistance in Europe, so blight clones are continuing to develop that are overcoming chemistry and genetics. It’s a constant battle to stay ahead and we must protect the chemistry we have by use of good anti-resistance strategies.

So far, the summer’s weather has not been conducive to the explosion of cercospora in sugar beet we saw last year. The British Beet Research Organisation (BBRO) model has not triggered any high risk alerts up to now, even though cercospora is present at low levels in many crops.

Cercospora needs high temperatures and high humidity, above 90%, to be become very aggressive and, as we well know, sunshine and high temperatures have not been that common this year. It was towards the end of August last year that we saw cercospora explode, with thunderstorms and temperatures in the high 20s to low 30degCs.

Thunderstorms are forecast as we run into September so we must not become complacent. Keep an eye on the crop and the BBRO warnings and react accordingly.

Last year’s cercospora issues were partly due to the crop being weakened by virus. But this season’s winter weather reduced the aphids and virus levels are much lower. Will the weather also help us with cercospora? Only time will tell.

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