Caring for compromised wheat

Challenging conditions last autumn are now presenting growers with difficult decisions for spring. Many might be considering what to do with, and how much to spend, on winter crops although nursing them through to harvest will be the aim of most.

With spring barley premiums looking unlikely, and no guarantee of good drilling conditions during March and April, winter wheat crops might still be the best bet.

Certainly, Stephen Harrison of South West Agronomy wouldn’t lock too many doors at the moment. He says there’s no magic cure, but some of the lost ground can be recovered. “With winter barley, yield is all about ears and the number of grains, so any crop with compromised tillers will always have a yield compromise as a result. With late sown winter wheat crops you can still be short of tillers and ultimately ears/m², but you can offset some of the lost ground by thousand grain weight.”

The starting point is to make sure there are enough nutrients in the soil once crops enter the growing phase. He advises growers to re-evaluate their nitrogen splits. “Rather than a typical 25 per cent total dose for a first application I would be looking at something in the region of 33 per cent. But don’t be tempted to go too early and check soils are warm enough for plants to take it up.”

In manganese-deficient soils, growers will have to be particularly vigilant. Mr Harrison says small rooted plants will struggle to pick up sufficient levels and he feels it would be a good idea to test soils.

Phosphate is another micronutrient to check for. “Ground temperature has a bearing on the availability of phosphate in the soil, so later drilled crops going into cooler soils could be short. It is important for rooting and growers need to determine soil levels.”

Disease control

Later drilled backward crops are likely to need lower totals of N this season, and an opportunity to retain crop margin. Disease control might be another. “When your fungicide programme starts this season depends on the threat. Septoria pressure is unlikely to be particularly high early season, so you may not need to get in until GS32.”

But for those that have susceptible yellow rust varieties, then an earlier start might be warranted. “It’s the juvenile stage that plants are at their most vulnerable and you can’t let the disease take hold. A fast moving azole or strobilurin would be useful to keep a lid on the disease and reduce transfer to yield bearing leaves,” he notes.

Another possible saving is azole + CTL at GS32. He feels it would have to be an exceptionally wet and humid spring for septoria pressure to be severe when the first yield bearing leaves emerge. “At GS32 azole + CTL is an option for varieties on the right side of ‘6’ for the disease.”

For him the obvious choices are prothioconazole or epoxiconazole. Which comes down to whether the target is septoria or yellow rust, but it’s spray gaps over fungicide choice which is more important with yellow rust. “If these are short then Proline (prothioconazole) with CTL is a good protectant. You can add in tebuconazole if you need to knock yellow rust back a bit.”

But he wouldn’t move away from azole + SDHI mixtures for flag leaf sprays. “The flag leaf is the most responsive in terms of yield and keeping it clean will be vital. You’ll want to prolong green leaf area as long as possible for bold grains.”

Weed control changes

Unfortunately, such savings on spring weed control may not be possible.

He fears a spike in spring weed pressure and warns that late drilled, backward crops will lack a competitive edge compared with those sown at more typical drilling dates. These thin, open crops will be particularly vulnerable to wild oats, but black-grass and other grass weeds could also threaten. In addition, late-drilled crops haven’t gone into the best seedbeds so uneven cloddy soils could be harbouring a higher amount of seeds than previous seasons.

“There has definitely been a shift in weed control strategies in winter wheat crops,” says Bayer campaign manager, Ben Coombs. “There used to be widespread spring application of Atlantis (mesosulfuron + iodosulfuron) to control black-grass but now a broader spectrum of weeds are in focus for spring applications.

“Where black-grass is a major challenge, control strategies built around cultural controls and pre-emergence herbicides like Liberator do the bulk of the work in the autumn. This means that spring is increasingly about tidying up any other weeds that are left,” he says. “Obviously, things will be slightly different this spring because of the abnormally wet autumn but I still expect other weeds to feature prominently in farmers’ planning.”

Chief among these are annual meadow-grass, brome and ryegrass. According to Bayer research, agronomists are particularly concerned about these weeds becoming more of a problem. Ryegrass is a worry because it has been shown to develop resistance to various modes of action. Thankfully, it is not as widespread as black-grass but farmers should be vigilant to prevent any infestation developing.

Brome is also a rising concern, particularly in the north and west of the country but also in the east. In most places, there are still effective cultural and chemical controls, but farmers are not always using them when focusing on other weed problems. Another factor is the reduction in post-emergence black-grass applications which were also controlling brome.

“I think the reduction in use of post-ems for black-grass control has been important in other weeds becoming more prevalent. Products like Atlantis and Pacifica (mesosulfuron + iodosulfuron) were effective against a wide range of grass weeds and also some broad-leaved weeds. When you take this out of the equation it follows that certain weeds become more of a problem.”

Broad-leaved weeds

Broad-leaved weeds are also a factor in spring. Overall, the chemistry is there to control them so it is more a case of selecting the right product and timing rather than worrying about if the weeds can be controlled. “Decision making is in some ways more complicated in spring than autumn because the picture is different on each farm. In autumn, farmers are finding strategies that, if conditions allow, work most of the time. In spring, it really does depend on the weed profile on the farm and the success of autumn control,” says Mr Coombs.

“Generally, the picture that has come back to us about spring is that farmers are controlling a mixture of weeds and looking to do it as soon as possible before moving on to T0 and the fungicide programme. As a result, farmers now have the option of Pacifica Plus (mesosulfuron + iodosulfuron + amidosulfuron), which has good control of grass weeds and many of the main broad-leaved weeds. As a single product co-formulation, we see it as a simple one product solution to the mixed spring weed situations we are now seeing.”

Post-emergence herbicides will be more important this spring because the usual foundation is not there, after the wet autumn meant many wheat crops didn’t get a pre-emergence.

However, in practical terms, using post-ems is no different to previous years with respect to waiting for calm, dry, conditions and active growth. The big difference is the potential range and number of weeds that need to be controlled so checking populations in depth before selecting a product will be crucial, says Mr Coombs.