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While monoculture crops have become the norm, this wasn’t always the case.
Going back more than a century, multiple cultivars of the same species were commonly grown together in the same paddock, a cultural practice that is again attracting the attention of researchers and growers.
Foundation for Arable Research cereals researcher Andrei Costan says that mixes have the potential to reduce disease pressure and spread, as well as increasing yield stability, and have been implemented with great success, particularly in cereals.
A three-way winter-sown feed wheat mix has been trialled by FAR at its Chertsey Arable Research Site near Ashburton, and some growers are also trying mixes.
At FAR’s Future Farm Systems Demonstration site at Chertsey, a three-way feed wheat mix was sown on the future farm side in autumn. This was an equal mix of three different cultivars, Voltron, SYDefiant and Graham, with the seed coated with Trichoderma. In contrast, the conventional side was only sown with Graham wheat.
A diversity of plant genetics in a paddock helps to reduce the rate of spread of pathogens compared with a traditional monoculture crop, Andrei says. “It creates a multiple gene obstacle course.”
“Cultivar mixtures have been successfully employed to steward disease resistant cultivars and at-risk chemistry, and to increase within-field diversity.”
No difference in management practices is required between the mixed and monoculture plantings, apart from the initial mixing of cultivars at sowing, with chemical inputs remaining the same.
There is no penalty in seed quality, and research shows a tendency for a minor yield increase with the three-way mix, mostly as a result of lower disease pressure, Andrei says.
However, farmers need to make sure they can market their harvest, as some mills may be hesitant to accept wheat mixtures, though this is less of an issue for feed wheat, destined for the dairy and poultry industries.
Another important consideration is making sure that the cultivars included in the mixture are compatible with each other, particularly in terms of time of ripening. Mixing early and late cultivars may result in premature shattering or the grain sprouting in the head (preharvest sprouting).
FAR research has focused on a mix of three cultivars, with data showing mixes of between three and six are possible. “Above six, there is little benefit from adding further cultivars for the work involved.”
A major obstacle in obtaining good wheat yields in New Zealand is disease control, with pathogens such as Septoria tritici blotch (STB) or leaf rusts causing severe yield losses if left unchecked.
As a result of challenges to arable farming, including increased pathogen resistance to fungicides and fewer new ag-chemicals becoming available, cultivar mixtures have seen a resurgence of interest. For example, in France, the use of wheat cultivar mixes rose from 1 per cent of the total wheat cultivated area in 2010 to more than 11 per cent by 2019.
Overseas research shows that when growing a mix, two-thirds of the selected cultivars should be resistant to the target disease and the other third more susceptible.
Sowing cultivars with different disease ratings in a mixture has several functions. Not only does it increase in-field diversity, but also the more resistant cultivar within the mixture can slow disease development, which in turn allows for flexibility in fungicide programme choice. This flexibility may help slow resistance development for at-risk chemistry. In addition, the inclusion of multiple cultivars relieves pressure on the more resistant variety, which can help reduce the risk of cultivar breakdown.
“If you mix together cultivars that are all resistant, this gives you the short-term benefit of disease reduction, but long-term you’re not really protecting the cultivars as much,” Andrei says.
From 2021, FAR carried out a three-year winter wheat cultivar mixture trial under irrigated and dryland conditions at Chertsey, funded by the SFFF “A Lighter Touch” programme. Three cultivars with different disease ratings to STB and rust were sown as a mixture in equal proportions. These were: year one - cultivars Firelight, Starfire and Graham; year two - Starfire, Firelight and Reflection; and year three - Starfire, Voltron and SYDefiant.
This showed that growing wheat cultivars in a mixture is an effective disease suppression method, regardless of whether the problem pathogen is leaf rust or STB.
“Thus, farmers who are growing feed wheat can consider cultivar mixtures as an option that will allow them to steward both at-risk chemistry and disease resistant varieties.
“Given the promising results, this opens up the possibility of future work, where we could test to see what the optimum number of cultivars is to include in a mixture, as well as what’s the best disease rating combination,” Andrei says.