The prolonged period of cold weather over recent weeks had restricted growth of all spring crops sown in late March. Whilst all germinated well, growth of most crops had been particularly slow. Rainfall has been adequate, enough to maintain good soil moisture ensuring even germination of crop and weeds, and not too much to cause any transient yellowing associated with plants struggling to take up nutrients in waterlogged soils.
The problem was very much the lack of heat, restricting nutrient availability and therefore growth and development. The pleasant rise in temperature this week has encouraged both weeds and crops to move rapidly. To date aphids have been discouraged from flying due to cool conditions but this will have changed this week with the sudden increase in temperature.
The well below average air temperatures up until now mean soil temperatures have also been well below average for the time of year. The Nitrogen mineralisation process in the soil where fertiliser nitrogen is converted to a form that can be taken up by the crop is a soil microbe process and therefore dependant on soil temperature. Hence colder soil has slowed the availability of nitrogen to the crop, and many other nutrients also, particularly manganese. Many crops are beginning to show nutrient deficiencies as a result.
The application of a broad-spectrum trace-element mix along with key macronutrients at this time is a very useful and beneficial way to supplement the plant’s nutrient requirements during periods of restricted availability, especially when coinciding with phases of rapid growth ie. during tillering and as stem extension begins. An application of a balanced and readily available source of macro & micronutrients that is not dependant on soil availability at this key time will minimise the adverse effects of restricted soil nutrient uptake.
Spring Cereals
To minimise the effects of competition on the crop and optimise the level of weed-control, the herbicide application should be carried out sooner rather than later, once all the weeds have emerged but are still small, and before they begin to compete with the crop for nutrients and light. Carrying out the weed control at the 2-4 leaf stage will lower rates of herbicide and give a much more effective result than delaying to coincide with the 1st fungicide application.
Product choice depends on the weed type and size present and crop growth stage.
Broad leaved wise, Sulfonyl-urea (SU) herbicides will likely be the starting point, controlling a wide range of weeds and are very safe to the crop.
Where the range of BLWs present are limited to chickweed, redshank, fat hen, fumitory & day nettle, the hormone mixture products will work well without the need to tank-mix, but must be applied by GS31. Where the likes of field pansy, forget-me-not, speedwells & corn-marigold are also present however, sulphonyl-ureas products will improve control. Conditions over the last week have been ideal for hormone products with consistent day and night temperatures. Compitox, Minstrel and Oxytril are the most widely used tank mix partners with SU’s.
Grass weeds are commonplace this season especially on head rigs, HUSSAR is the only product now available to treat AMG in spring crops, controlling it up to the end of tillering. It also gives very useful suppression of wild oats that are emerged at the time of application (further plants are likely to emerge later). It also controls a range of BLW very similar to the other SU’s.
If clover is part of the mixture, a clover safe product must be used. TRIAD is a new clover-safe herbicide available for the first time last season. Whilst currently labelled for use in ‘Spring Barley undersown with IRG’ only, a new wider label is currently going through the approval process reading ‘Spring Barley undersown with grass, and grassland’. If seedling docks, thistles and buttercup are also problem weeds, SPRUCE must be added to the TRIAD to improve control of these also. SPRUCE is 2,4DB, a clover safe hormone type herbicide.
Winter Barley
Rhyncho is present in most crops at various levels depending on the disease control already applied. The cool and damp weather pattern over the last month has been ideal for this disease, and without a robust and properly timed fungicide application this disease will move rapidly up the plant onto the upper leaves, awns and heads. Mildew is also present at varying levels. Ramularia is also beginning to show, with newer varieties showing greater sensitivity to this late developing disease. It tends to show late in the season usually after booting, symptoms are very similar to manganese deficiency.
The SDHI chemistry now available have a good position at T2 on winter barley crops where they retain green leaf and are very active against Ramularia. However whilst Bixafen (Bayer) and xemium (BASF) have curative activity, triazoles are still essential to the core of the T2 fungicide mix, with prothio, epoxi and flusilazole being the most robust for Rhyncho, both preventative & curative The SDHI actives are more long lasting than other chemistry groups, providing enhanced disease control and extending the protection period by up to 3 weeks. They also give consistent increases in green leaf area in the field, delay senescence and improve drought tolerance, all components that build yield.
Bixafen, available in mixture with prothioconazole as SILTRA for barley is particularly strong on Rhyncho. Xemium is also very strong but its partner triazole in ADEXAR, epoxiconazole is not as strong as the Bayer triazole. BASF also have boscalid, another SDHI active available in mixture with epoxiconazole as CHORD. Whilst the boscalid is not as curative as xemium, CHORD is very strong on Rhyncho and also has excellent activity on Ramularia at T2. Isopyrazam (Syngenta), in mixture with cyprodinil as BONTIMA for barley is particularly strong on rusts. None are particularly strong on Mildew or Fusarium.
Chlorothalonil is still an option when used preventatively to improve Ramularia activity but only when an SDHI is not being used at T2. (It has no activity on any other barley diseases.) FIELDER is an ideal triazole partner, combining both TALIUS and chlorothalonil in the one pack to control both Ramularia and Mildew Where the SDHI chemistry is not being used, strobs also have a very important role in the T2 fungicide programme in those crops with good potential, improving control of Brown Rust, Net Blotch & Rhyncho. With a different mode of activity to the triazoles, it is an excellent partner in resistance management.
Winter Wheat
Most crops have now moved through the stages of stem elongation.Septoria tritici is present in all crops at variable levels depending on T1 timing. Mildew is also present in all varieties depending on whether TALIUS has already been applied.
The flag leaf will be emerging in most crops within the next week or two, and this is the key time to apply the T2 treatment. Of all fungicide treatments, T2 gives the greatest response in terms of grain yield and quality, keeping the top three leaves clean and the ear as it emerges. For this reason the manufacturers are targeting their new SDHI chemistry at this timing when the big spend will give the greatest return. Trial work on both sides of the Irish Sea last year showed consistently higher yields when these products were applied at this time.
While not as curative as the triazoles, each manufacturer claims extended persistency against Septoria for their SDHI actives. Co-formulated with triazoles, they all show excellent Septoria activity as well as extended activity on rusts and in the absence of disease enhance green leaf retention (similar to strob activity), so boosting grain-fill. Whilst their disease performance is not enhanced by the addition of a strob or chlorothalonil at this timing, from a disease resistance management point of view chlorothalonil should continue to be added.
Epoxiconazole and prothioconazole remain the key triazoles for controlling Septoria. However the difficulty in controlling this disease should not be underestimated. Part of any pathogen’s survival mechanism is to change in response to outside influences that adversely affect its development, and the Septoria pathogen is continuously modifying itself in response to a fungicides’ mode of action, developing ways around it. Population strains of the Septoria pathogen continue to change. New genetic variants are more able to tolerate particular fungicides, becoming harder to kill with epoxi and prothio (Group 1 triazoles). However these same strains are easily controlled with certain older triazoles including tebuconazole and metconazole (Group 2 triazoles). Hence the rationale for the best performing triazole products in recent years to be co-form triazole mixtures. In PROSARO, Bayer have demonstrated over the last 3 years that the effect of two triazoles mixed together is greater than the sum of both when used separately, the tebuconazole improving the product performance on Septoria over straight prothioconazole. BASF have identified a similar effect with BRUTUS, a mixture of epoxiconazole and metconazole. This product consistently outperforms straight OPUS, gram for gram and produces results in the field similar to PROSARO.