Plant health focus

By Professor Fiona Burnett,

Head of crop and soil systems SRUC

FOR MANY diseases, their risk to spring barley is lower than in the winter crop.

It doesn’t carry foliar disease through the winter, nor is it at the same risk of stem base disease and take-all as the winter crop.

But, the risk of ramularia is proportionally higher as one of the main diseases in the spring crop, so control choices are critical. That’s especially so this season when there are emerging fungicide resistance risks in the disease.

There were issues with fungicide resistance to azole and SDHI chemistry at trial sites in Germany and Denmark last year. SRUC data has confirmed a shift in Scottish ramularia samples gathered in 2016, so we go into this summer uncertain about the efficacy of azole and SDHI chemistry.

The best advice in a moving situation such as this, is to use a mixture of chemistry so that no one active is over exposed.

If the risk of ramularia is lower on more resistant varieties, then reducing doses is a better strategy than taking a component out of the tank. The addition of a multi-site to support the two suspect actives is of increased importance this season.

Chlorothalonil has done consistently well in SRUC trials at retaining green leaf and protecting against ramularia. It is a win:win with regards to fungicide resistance management as it has very low risk of resistance development itself. I

t is worth noting that strobilurins are ineffective against ramularia and they do not offer any support in this situation.

Spring barley gives a nice opportunity to think of IPM practices – just by dint of spring drilling, growers have already reduced the risk of stem base and early season foliar disease compared to the winter crop.

A move to Laureate, which is rated 6 for rhynchosporium and 7 for ramularia brings more use of varietal resistance to the IPM basket, than, say, Concerto which is rated 4 and 6, respectively .

That, and the dry weather early in crop growth this year reduced the risk of early foliar diseases, such as rhynchosporium and the fungicide options for ramularia at T2 will give continued protection against a wide range of foliar diseases.

The high rainfall already in June has again brought the risk of ear diseases in a wet summer in to focus. Unfortunately, the timings used to target ramularia at booting means that the ear is not directly targeted in spring barley.

There is some scope to move this spray back to early ear emergence, but check last application timings carefully as many have latest timings before ear emergence or before flowering, depending on product.

Later applications to the ear are too late to manage ramularia and do not help with yield or quality even in a wet summer, as shown in SRUC trials, funded by the Loirston Trust.

SRUC’s ramularia warning

Earlier this year, crop protection company, Bayer, announced that some crops in Germany and Denmark that were infected with ramularia collo-cygni fungus were not responding to normal treatments containing triazole and SDHI fungicides.

The SRUC studies indicated Scottish barley faces a similar threat if farmers do not make adjustments to their treatments.

This strain causes ramularia leaf spot disease, particularly in spring sown crops, but it can affect autumn-sown crops.

Well-established protection based on triazole and SDHIs, but ‘unless farmers take action there is a real risk that the fungicide resistant ramularia strains will build up causing major problems in future,’ said SRUC’s senior plant pathologist, Dr Neil Havis.

“Our research shows that the fungus is still sensitive to cholorothalonil, so we recommend adding into into spraying programmes, particularly at T2 timing.”