In this month’s Crop Walk and Talk Christine Lilly, Frontier Agriculture, highlights the agronomic issues affecting wheat, barley and oilseed rape crops in Cambridgeshire. Abby Kellett reports.
Following a period of reasonably high disease pressure, winter wheat crops appeared to have been relieved of some septoria and yellow rust pressure in particular as a result of recent cold weather.
According to Miss Lilly there is no need for a pre-T0 fungicide application on wheat at the site. However high levels of brown rust and potential mildew infestations mean a pre T0 application may benefit winter barley crops.
Otherwise, fungicide application should be left to the T0 timing, which is expected to be towards the end of this month, with crops approaching growth stage 30.
After uncertainty regarding soil nitrogen levels, she expected soil nitrogen demand to be similar to previous years.
She said: “In terms of the total dose of N, it is probably not that different normal. It has been a mild winter so there will have been more mineralisation, but to contrast that, we have seen some heavy rainfall.”
While wheat crops drilled on October 10 looked to be approaching GS30, she said more forward crops, may have reached this stage already.
The most prevalent diseases identified at the site included yellow rust and septoria, although levels have recently decreased.
“Levels of yellow rust have dropped quite considerably from where they were a few weeks ago when we could find it readily in about 30 to 40 varieties.
“The recent colder weather has slowed it down, although we are still finding some."
She also warned that yellow rust could show resurgence once warm weather returns.
Looking ahead to the T0 timing, she suggested applying a triazole-chlorothalonil mix to control yellow rust and septoria and advised growers to pay close attention to mildew development.
“Mildew could quite easily start to develop in some of the more susceptible varieties such as Leeds. If it does, it may be worth putting a mildewicide in the mix at the same time.”
In terms of N application, she advised growers that have not already applied N, to do so as soon as possible and suggested a modest application would be sufficient in encouraging crop growth.
“Crops just need a small dose, 40 to 50 kg of N is sufficient, just enough to get the crop started."
In addition, recent trials have indicated that there is an increasing demand for sulphur application.
“There is now plenty of evidence to suggest most crops will require an application of sulphur. If soils are deficient, it is important to get at least some sulphur applied within the first application timing.”
When assessing herbicide trial plots, black-grass was evident in both treated and untreated plots.
Where no herbicide was applied, black-grass was beginning to tiller out with some plants boasting eight to nine tillers already. Ms Lilly predicted there would be high numbers of heads appearing in these crops come the summer.
In treated plots, black-grass plants were still present, despite an application of Avadex (tri-allate) granules in the autumn.
Therefore, unless a robust herbicide programme has been adopted, farmers may need to apply further chemistry in order to sufficiently control the weed.
“There is not a lot of options in the spring, however applying products such as Atlantis and Pacifica now may be effective depending on the resistance and size of the plants,” she said.
Although there appeared to be large variation in the development of barley crops, on closer observation, most varieties were nearly at GS30 and presented around five to six tillers.
Unlike wheat, disease levels were fairly high, particularly brown rust incidence. While mildew was not apparent in crops on this sight, Miss Lilly said that in other areas mildew activity was much greater.
Given the level of disease, she suggested using a pre-T0 fungicide to gain good control of both the mildew and brown rust.
“Disease in this crop is at a sufficient level to justify using a pre-T0 application, something we have seen benefit from in the last couple of seasons, particularly in controlling brown rust and rhynchosporium.
“As we move forward to our T1 timing, prothioconazole should be included in the fungicide programme to give control of rhynchosporium and net blotch as well as an SDHI fungicide.”
For growers that did not gain complete control of broad-leaved weeds in the autumn, weed-specific herbicides should be applied in the next few days.
“Cleavers may be starting to become an issue so a specific cleaver control product should be used. If you have a range of broad-leave weeds then a combination of SU chemistry will be more appropriate,” she said.
Where soil conditions have allowed most farmers to apply at least some N, allowing deficient barley crops to recover. However, manganese deficiency symptoms have become apparent in the last two weeks, according to Miss Lilly.
“If you have not applied any manganese onto crops, it is important to get that on now, particularly if there is a known deficiency. In some cases, multiples applications may be required to aid crop recovery.”
Oilseed rape crops were fairly advanced with some of the most forward crops approaching the yellow bud stage. Although, she acknowledged that there is large variation across the country, with some later-drilled crops barely moving into stem extension.
This variation was also observed on a field scale at the site: “The growth stage of plants within the field is also very variable as a result of secondary germination.
“However, over the next few weeks, crops should start to even up and branch out.”
Light leaf spot was identified as the prevalent disease in OSR this month, although at this particular site, its incidence was low.
“If anybody has not applied a fungicide this spring, then it is important to get some onto the crop.
See also: Keeping ahead of light leaf spot
However, she warned that growers should be cautious when considering using fungicides that have PGR activity.
“If you have got crops that are stressed or backward, you probably want to avoid products with too much PGR activity, because we have seen negative effects on yield where they have been applied unnecessarily.”
She also advised growers to monitor pollen beetle numbers as the pest’s activity is anticipated to be high this spring.
Only where incidence is high will action be required to avoid a potential yield penalty this spring.
“You need some quite high numbers to justify treatment because it is remarkable how much OSR can recover.
“If you do find the pest at high levels, you need to be thinking about putting an insecticide along with the fungicide, while also bearing in mind what you can and can’t mix,” she said.