Contrasting fortunes of fungicide and herbicide developments
The arrival of another new SDHI fungicide means that growers can look forward to getting more than just disease control from their spray programmes in 2012, said Bill Clark, director of Broom’s Barn.
Adexar, from BASF, joins Bayer’s Aviator and Syngenta’s Seguris in the marketplace, he pointed out, giving growers even more choice and offering performance improvements over existing chemistry.
Additional yield responses are in the region of 0.3-0.4t/ha from a single SDHI spray, he noted, adding that two sprays produce an extra 1t/ha on average, when compared with a triazole-based regime.
“Growers are in a good position,” he noted. “They can still get good disease control from the triazoles, despite a slight decline in performance, but they can get even higher yields with the new chemistry.”
This is because the SDHIs add value to fungicide programmes, he continued. “There are physiological effects from all of them, which are most obvious in the crop greening.”
In the plant, these effects include higher rates of photosynthesis under drought conditions and quicker recovery of stomatal conductance, reported Mr Clark. “In addition, crops are also able to access water from depth, due to their deeper rooting characteristics.”
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Furthermore, the SDHIs are more eradicant than first thought, he added. “The HGCA work, which tests their protectant and eradicant activity, has shown that you can get good curative septoria control from them.”
Even so, they must be used in mixtures, to protect them from resistance, he advised. “Boscalid has been available since 2003 and there’s been no sensitivity change in septoria. But growers shouldn’t be complacent.”
Hutchinsons trials with SDHIs last year showed yield responses even where disease was absent due to the drought, confirmed David Ellerton, Hutchinsons technical director.
“Responses to fungicides in 2011 were about one-third of the level that has been seen,” he said. “The very cold winter, followed by an exceptionally dry spring, almost stopped disease in its tracks.”
This was most obvious in the east, where responses from SDHI/triazole/strobilurin mixes used at both T1 and T2 were between 0.6-0.7t/ha, he said.
“But over in Shropshire, where there was a bit more moisture, we recorded a 2.82t/ha yield response from the same programme. So we know that there’s more to come.”
Grass weed control
The diminishing availability of herbicide options for blackgrass control is forcing growers to concentrate their efforts on the period between combining and drilling, said James Clarke of ADAS.
Without any new chemical solutions, the use of weed dormancy and germination information, together with rotational control, will help, he suggested.
“Weeds generally emerge from the top 5cm of soil only,” he said. “So it is possible to manage the seedbank with your cultivation strategy.”
Shallow till and no-till systems tend to keep the weed seeds in the top layer of soil, where they can germinate freely, while ploughing and deep till systems bury new seeds. “But many old seeds are brought to the surface. These are only a threat if they have good longevity, and this varies between weed species.”
Dormancy information can then be added to the cultivations approach, continued Mr Clarke. “If you know that it’s a high dormancy year, it’s usually best to plough. You can also use early drilling, to make the most of crop competition.”
In a low dormancy year, shallow cultivations have a place, together with delayed drilling. “In this situation, the timing of the pre-emergence herbicide is very important and needs to be close to drilling.”
Emergence data is useful for improving the timing of the post-emergence herbicide, he added. “This year, monitoring work has shown us that the last week in November was the best time for the post-emergence blackgrass spray.”
Work conducted at Hutchinsons blackgrass trials site confirmed the importance of soil movement last year, both in the season of use and in the following crop, said technical manager Dick Neale.
“Where we didn’t move soil to depth, we achieved better blackgrass control,” he reported. “The deep tillage plots were the ones with the most problems.”
Very good results from pre-emergence herbicides alone in 2010 are unlikely to be repeated this year, he ended. “We’ve had very different conditions. Blackgrass has been slower to germinate and the dry autumn meant the pre-emergence treatments haven’t worked as well.”