Timing issues could compromise yield

Again, April turned out to be a record breaker, with sun hours of 216.6 topping the previous high of 204.6 in 2020. As disease on the lower leaves of wheat and barley crops dried up, farmers and agronomists pondered products and rates for T1 sprays

One of those was Sandy Dale, of Scoughall, East Lothian. With September-drilled Elation, Skyscraper and Insitor, septoria pressure would have been a concern coming out of the winter. But as dry, cool conditions prevailed so disease pressure slid away and as a result Sandy hoped to reduce T1 rates for Insitor over Elation and Skyscraper.

The reduction in disease pressure was confirmed courtesy of Bayer’s National Snapshot. He is part of a group of farmers across the UK and Ireland who are using Rapid Disease Detection (RDD) to measure disease DNA in leaves. Both Elation and Insitor carried some disease earlier in the season, but nothing significant, peaking in Elation in mid-March at 0.932 pg/ul. As T1 approached, leaves 6 and 5 were revealed to be clean.

However, the hope of reduced rates was dashed by weather. Sandy had his spraying window reduced to just one day and needed to build in herbicide and growth regulator requirements at the same time. “Our autumn weed control was compromised and I just didn’t have the time to match herbicide and PGR rates by field,” he said.

But that window coincided nicely with GS32 and leaf three emergence. With the potency of an SDHI in T1 mixes and a short gap to T2, he felt he might have some rate flexibility. “RDD picked up some disease in leaf 5 but it isn’t significant at the moment. It means I’m likely to have some options on products and rates at T2.”

Testing in the first week of May revealed leaf 5 of both varieties carrying similar levels to those of mid-March. With pg/ul of 0.804 in Elation and Insitor at 0.703 pg/ul both are still in the amber category but he will monitor both weekly. Although he might have the option of some rate flexibility, he will include an SDHI – “The top three leaves contribute the most for yield. I’m not looking to take any chances.

“I’m happy to opt for a high investment strategy. Any incremental gain is likely to outweigh additional input costs. I’m also considering another application of magnesium with T2 sprays to boost chlorophyll production,” he noted.

That applied to Insitor. Despite a septoria rating of 6.8, he saw varietal resilience as further insurance if something goes wrong. “These varieties still needed to be supported by an appropriate fungicide programme. But it buys some time if I’m delayed due to the weather.”

But not everyone has been so lucky with T1 timing. With many T1s going on late and a possible short gap to flag leaf emergence, Bayer’s Craig Simpson said a delayed T2 could be inevitable in some situations given potential weather interruptions and other farm tasks at this important time.

He advised growers to stick with GS39 – full flag leaf emergence – with it being the most important fungicide timing. But he suggested it wouldn't be a disaster if it was delayed providing growers use the appropriate products and robust rates. “Those later T1 sprays may have hit leaf 2 so it is going to offer some protection to the upper canopy. But protection of the flag leaf is crucial, so a strong septoria product, ideally with fusarium activity, is the ideal.”

He felt that Ascra’s (prothioconazole + bixafen + fluopyram) broad spectrum activity was good value in a delayed T2 situation, but would look to up the rate to 1.2 l/ha or higher. He acknowledged that with the arrival of Inatreq (fenpicoxamid) and Revystar (mefentrifluconazole + fluxapyroxad) growers had strong septoria products to select from, but warned that neither was as active against fusarium. “With a T2.5 you have to factor in fusarium and there isn’t a better option than prothioconazole,” he pointed out.

Septoria is now beginning to show up on the lower leaves of Skyscraper in the Lothians

The issue of timing is a concern with T3 sprays too. SRUC’s Professor Fiona Burnett was worried that with compressed timings pushing back T3 sprays, it could leave crops a little open. "A short gap is almost inevitable as crops try and catch up. By the time we are at flowering, it is all about day length and we must remember it is a long time to harvest,” she argued.

Craig also warned not to discount yellow rust, given Scotland's cooler climate. “Last season the disease was easily found in Scotland during and post flag leaf emergence, so it wouldn’t be a bad idea to build in some protection. Again, prothioconazole products are a good option, especially when supported with bixafen and fluopyram,” he said.

Both septora and yellow rust had been detected at SRUC trials at Boghall, Midlothian, wheer Skyscraper is carrying both diseases on leaves 5 and 4. Leaf 5 is carrying quite high levels of septoria, recording 3.123 pg/ul, with leaf 4 significantly less.

It did not surprise Professor Burnett, who said that just a few days of wet and warm weather could set it off again, but encouragingly for May it is still confined to lower leaves. Yellow rust is present, but at extremely low levels and T1s kept it in check.

Bayer’s Grant Reid agreed that temperatures hadn't been helpful for septoria, but felt a period of warmth and continued showery weather could help push the disease on to leaf 3. “Although septoria pressure has been light so far, we’re not completely in the clear. Some significant rain events could splash the disease in the lower canopy up onto the top leaves with some wheat crops only ‘knee high’,” he argued.

RDD had picked up yellow rust in Skyscraper. It is one of a number of varieties where ratings are being questioned, but he did not see a repeat of its problems in 2020. “DNA levels are extremely low – in leaf 4 just 0.13 pg/ul. However, for those with varieties where ratings are poor, or are in doubt then factoring the disease into T2 sprays is a sensible precaution,” he said.

Rhyncho hanging on

With April’s sunshine record you’d be forgiven for thinking rhynchosporium wouldn’t be a concern in barley, but it is a slight worry for Professor Burnett. Ahead of winter barley T1 sprays, she was concerned at the levels at the Boghall trial site, and that is still the case. It is a little intriguing as the cool, dry weather has reduced the Ramularia threat to Winter Crops.

With much of the spring crop late drilled and late emerging disease risks are currently low, but recent rain has helped move them on. Fortunately, she notes the stress spring crops have been under is too early to trigger Ramularia.

Bayer’s Grant Reid says regardless of whether a T1 has been missed or omitted, the T2 timing is critical with spring barley. “I consider this as important as product choice. You’ve got to protect the awns so it is important to spray at the extending stage. Too early and protection will be impaired, too late and some disease could be established.”

And he warns growers the gap from T1 could be short. “As the ground dried out during March and April the lack of moisture held crops back. But with warmer weather they could race on. The gap from T1 could be short this season.”

Where product choice does take on particular significance is where Rhynchosporium threatens. With the disease seen early in the season in winter crops and reported in the base of spring crops wet weather could see it spread and move into the upper canopy. “Trifloxistrobin and spiroxamine remain good partners for prothioconazole but don’t quite match an SDHI when it comes to Rhynchosporium. Prothioconazole plus bixafen is a hard combination to beat,” adds Mr Reid.

Weed control

A consideration for Sandy with T2 winter wheat sprays is a weed ‘top up’.

With ‘back end’ weed control compromised by wet autumn weather it has resulted in ongoing concerns with Bur chervil and Brome. He believes Brome is under control but feels he might have to come in again with Bur chervil. “I’m learning that if it gets established it is difficult to eradicate it.

“One problem is there isn’t a herbicide mix that can be put together to deal with both so I’ve had to target separately at the T0 and T1. The brome looks to be under control but Bur chervil is a concern and I might have to come back in.”

A second season where autumn weed control has been hindered by wet weather means a possible re-think around drilling and autumn weed control strategies. “Hindsight is a wonderful thing but it has taught me holding on for good weather is a risk. It might be better to prioritise activities around autumn spray windows even if it means having come off the drill.”