In this month’s Crop Walk and Talk Jon Allard, agronomist with Frontier Agriculture, highlights the agronomic issues affecting wheat, barley and oilseed rape crops near Ross on Wye, Herefordshire. Abby Kellett reports.
Despite early spring offering a drop in temperatures, where T0 fungicide applications have been delayed or absent, disease pressure is likely to be high.
At the site, winter wheat crops were fast approaching the T1 fungicide timing, with most plants identified at growth stage 31, while winter barley crops had already had their T1 applications.
With the T1 timing imminent, assessing disease levels was an integral part of this month’s crop walk, in order to plan a fungicide programme that would provide adequate protection of leaf 3.
As with most regions, recent wet weather had promoted the spread of septoria spores, even in varieties with good resistance ratings against the disease.
Mr Allard said: “Generally there is a lot of septoria pressure in Herefordshire. We have had a lot of rain this month and temperatures have been relatively cool, providing optimum conditions for septoria spreading.
“The variety Cougar has a relatively good disease rating for septoria, but even in this crop there is a fair bit of septoria in the base of the plant.
Although disease was identified at high levels in the base of wheat crops, younger leaves appeared reasonably clean.
“We want to stop disease moving up into the top of the canopy because we have some relatively clean leaves. Leaf 3 and 4 look clean and we want to keep it that way,” he said.
Apart from septoria, yellow rust has been prominent across much of the UK, with some of the more susceptible varieties such as Reflection, Kielder and Leeds showing the highest level of infection, according to Mr Allard.
In response, he plans to treat crops with a combination of active ingredients: “At the T1, I will use a multi-site protectant like chlorothalonil and tank mix it with an SDHI and a triazole in order to control yellow rust and septoria.
“It is a fairly high disease pressure year so we will be maintaining of all those active ingredients as part of an anti-resistant strategy and also to match disease pressures.
Another consequence of the mild winter has been increased pest activity. Where wheat crops have followed high risk crops such as OSR, slug damage was particularly evident.
However, Mr Allard urged growers to delay treatment until post-harvest, as any effect on this year’s crop yield would be non-recoverable.
“In terms of yield, there is no point treating for slugs now. Instead, farmers will have to protect the following crop, particularly during the early stages of establishment.”
While adequate control of most grass-weeds has been achieved, a number of broad-leave weeds were identified including fumitory, mayweed, groundsel and volunteer OSR.
Although weed numbers were not as high as he expected, levels were sufficient to warrant another herbicide application along with the T1 timing.
Additionally, the crop will receive a secondary PRG application at the T1 timing in order to concentrate energy on apical development and to reduce the risk of lodging.
Barley crops with previous nitrogen deficiencies have recovered well in response to fertiliser application, with yellowing more limited to stressed parts of the field such as headlands.
In terms of disease, rhynchosporium infection was present at high levels at the base of the crop. However the recent T1 application, which consisted of a triazole, strobilurin, SDHI formulation, was expected to control any further movement of the disease.
Mr Allard said: “There was quite a lot of rhynchosporium in the base of the crop earlier on in the season but we seem to have got it under control. Although there is a little bit that has been moving up the plant.
“Now that the T1 has been applied, we should be on top of the rhynchosporium.”
As with winter wheat, BYDV has been problematic in barley crops this season, but symptoms including leaf yellowing, have only recently been visible.
“BYDV has been a real issue this season because we have had a relatively mild autumn and winter which has increased aphid activity.
“There has been quite a lot of BYDV starting to express over the last month, which is quite severe in some barley crops.”
While weed infestations were comparable to winter wheat crops, the inclusion of a broad-leaved weed herbicide along with the T1 fungicide was successful at removing the majority of weeds present.
Unmistakably, OSR crops were at the early flowering growth stage, at this point pollen beetle is of little threat to the crop despite high numbers, according to Mr Allard.
Nevertheless, he urged farmers to keep an eye on plants which are still at green-yellow bud stage, which is when the pest poses the greatest risk.
“We still have some plants at green and yellow bud so we need to keep an eye on pollen beetle levels.
“In this field we have reasonable levels of pollen beetle, but given the colder recent temperatures and the fact we are heading towards mid-flowering, the pollen beetle levels aren’t such that we need to worry about putting an insecticide on.”
In the coming weeks, he advised growers to turn their attention to sclerotinia, which should be treat at mid-flowering, when there are 15 to 20 pods set on the main raceme.
“Soil temperatures are still a little bit cool so sclerotinia germination has not begun yet.
“In this field of oilseed rape, we haven’t got any pods set, so we are a little bit away from applying a fungicide.
“We will need to monitor soil temperatures because as it increases, the sclerotinia spores are released and they infect the plant early, which means an earlier fungicide application may be required in order to protect the plant.”
On assessment, new growth was relatively clean, despite high disease pressure particularly from light leaf spot.
See also: Keeping ahead of light leaf spot
“Although there is evidence of light leaf spot on older leaves, new leaves appear fairly clean despite high disease pressure in early spring.
“Applying a timely fungicide treatment will be important in making sure infection from older leaves does not spread to new growth,” he said.
Green area index (GAI) assessment revealed a GAI of around 2.5 which is adequate at early flowering, assuming the target GAI is 3.5 at mid-flowering.
“When the crop gets to mid-flowering we need to be at about 3.5 and currently we are at 2.5. By the time we get to mid-flowering, I am anticipating that it will have put on another point on its GAI score.
“By achieving this, we will be looking at 7000 to 8000 pods per square metre which is considered the optimum in terms of yield potential."