• The 9 foundations of second wheat success

Growing second wheat comes with considerable risk and in some cases can result in a hefty yield penalty over first wheat.

But identifying risk and using all management tools at the growers’ disposal can help bridge the gap and make wheat the most profitable second-straw option on farm.

Rotations have been evolving over the past decade or so due to various pressures, including the rise of oilseed rape, tough-to-control blackgrass and, more recently, the three-crop rule.

See also: Learn how to plough to bury your blackgrass

Winter feed barley has perhaps been the biggest winner, offering a spread of workload, early entry into rape crops and very attractive yields as new high yielding two- and six-row varieties are introduced.

The crop has squeezed out second wheat on some farms, along with spring-sown cereals where blackgrass is a particular concern.

However, where winter wheat remains the second cereal of choice, driving yield as hard as possible should be the priority to ensure that the higher input, lower output option pays its way, according to Agrii’s seed technical manager David Leaper.

“The economics of second wheat is first and foremost in growers’ minds and we need to look at all means available to improve yields and bridge the gap to first wheats,” he explains.

According to the company’s analysis of on-farm data and projections for the 2016 harvest, an example 200ha wheat enterprise with a 60-40 split of first to second wheat would lose £9,000 (£45.60/ha) from growing a poorer second wheat (see table below).

“Second wheats grown badly are a non-starter, but second wheats done well are sustainable in the right circumstances,” he explains.

Assessing risk

According to AHDB Recommended List trial data, the mean yield loss from growing second wheat over the past five years is 1.5t/ha and this is caused by a number of factors.

Second wheat can suffer from increased carryover of rusts, mildew, sharp and true eyespot and barley yellow dwarf virus (BYDV), along with grassweeds if they are poorly controlled in the preceding crop.

But the single biggest yield robber is the soil-borne fungal disease take-all, which colonises roots and hinders water and nutrient uptake and the management of this devastating disease is crucial to second wheat success.

Take-all severity is influenced by weather, with warm winters followed by a wet spring and early summer encouraging build-up of the fungus.

It is most severe in second and third wheat crops, but other cereals such as barley, triticale and rye, along with grasses such as ryegrass, blackgrass and brome, also provide good hosts.

Soil type will also have a dramatic impact on the disease (see below), with peats, black sands and high organic matter mineral soils providing the most risk.

Although they are relatively unaffected by the disease, they allow a build-up or carryover into to successive wheat crops and have the potential to reduce yield by 5-15%.

Growing successful second wheat is the perfect example of integrated crop management and variety is the first and foremost consideration according to Limagrain’s wheat breeder Ron Granger.

He explains that it is extremely difficult to breed varieties specifically for the second wheat slot, as the root disease complex – which includes take-all, eyespot and fusarium – is notoriously sporadic and very season-dependent.

However, there are clear differences between varieties in the second wheat position when scanning through Recommended List data and Mr Granger believes that growers should start thinking about their first and second wheats as a double act.

“If you have a variety in the first wheat slot that allows a high build-up of take-all inoculum it is going result in a high level of inoculum going into the second wheat,” he explains.

Mr Granger says past Limagrain trials have suggested that the Pch1 “Rendezvous” true eyespot resistance gene not only copes with eyespot, but also reduces take-all build-up.

This could be useful in a first wheat situation where it is due to be followed by another wheat and such varieties include Group 1 milling wheat Skyfall, soft Group 4 Revelation and hard Group 4 feed variety Grafton.

“Robigus is an example well known for its susceptibility to take-all and growing two in a row would be the ‘kiss of death’. If you grow a more tolerant wheat first, you should get a better result,” he says.

Seed treatment

Once the correct variety is chosen, seed treatment is crucial element to second wheat success according to Monsanto’s Barrie Hunt, with two options available.

Fluquinconazole + prochloraz-based Jockey can offer good suppression of take-all in second wheats, but both independent and manufacturer Monsanto’s trials suggest that silthiofam-based Latitude offers the best and most consistent results.

“A seed treatment won’t mean no take-all infection, but it delays the onset of the disease and gives crops a flying start.

“Over 13 years of trials we have seen an average yield response of 0.5t/ha over a single purpose dressing, driven by a 13% higher root mass and 20% increase in ears per plant,” explains Mr Hunt.

Mr Leaper says that in the past Latitude has been used as a tool to reduce the effect of take-all on early first and second wheats in high-risk situations, but there is still a significant benefit in the lower risk, later drilled slot.

Colin Lloyd

While variety selection and seed treatment are two critical factors in successful second wheat, Agrii’s technical manager Colin Lloyd (left) says there are also some small things that will help bridge the yield gap to first wheat.

1. Establishment – You can’t make a good crop out of poor establishment and the better performing second wheat growers are paying attention to their soils. “We have seen the best second wheat results on land that has been worked with a plough or deep cultivation.”
2. Drilling date – There is a close correlation between drilling date and incidence of take-all, with a slight decline in the second wheat when establishing the crop later in October. Mr Lloyd says you won’t manage to eliminate the problem, but it helps reduce the risk and has the added benefit of improved grassweed control.
3. Seed rate – The general reaction when sowing second wheat is to increase seed rates, but the best growers are looking to use lower seed rates, while choosing well-tillering varieties that move quickly in the spring. High seed rates lead to root crossover and the perfect environment for secondary take-all spread.
4. Nitrogen – High nitrogen rates in second wheats are thought to compensate for poorer rooting caused by take-all, but the top second wheat growers are now focusing more of their total N earlier. Aim for about 40% as soon as there is growth in the spring – around late February or early March. Using ammonium-derived nitrogen, such as ammonium sulphate, could also help supress take-all by lowering soil pH in the root zone.
5. Phosphate – P deficient soils favour take-all, so growers should attempt to correct any deficiency ahead of the second wheat. Seed- or foliar-applied phosphite can increase rooting and encourage P utilisation to counter the effect of take-all. It’s an in-season “agronomic cheat”, says Mr Lloyd.
6. Manganese – Work carried out in the US suggests that the take-all fungus can inhibit the uptake of manganese and, therefore, applying fresh manganese that is available to the plant will help reduce plant stress. It is essential to get manganese on to second wheat early in its development. Copper is also a micronutrient to be addressed.
7. Disease control – Although no foliar-applied fungicide will eradicate soilborne diseases, strobilurin fungicides such as azoxystrobin and pyraclastrobin can help supress take-all when used at high rates and early in the spring at the T0 (GS30-31) spray timing. The use of certain SDHIs has been shown to result in a “greening” effect and increased rooting, which will help. Building in an eyespot active azole such as prothioconazole early in the programme will give extra stem-based protection.
8. Plant growth regulation – An early PGR such as chlormequat will help increase fresh root weight and more healthy roots allow the plants to cope better with the presence of take-all.
9. Volunteer and grassweed control – Controlling cereal volunteers and grassweed hosts such as blackgrass and brome throughout the rotation will help to reduce the levels of take-all build-up in the soil. A first wheat after a weedy break crop could still be at significant risk from the disease.