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Time For Weed Control in Spring Crops

The prolonged period of cold weather over recent weeks had restricted growth of all spring and winter sown crops. Whilst all germinated well, growth of most crops has been particularly slow. Rainfall has been adequate, enough to maintain good soil moisture ensuring even germination of crop and weeds, but surprisingly 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. To date aphids have been discouraged from flying due to cool conditions but this can quickly change as temperatures improve.

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-urea products will improve control. Grass weeds are commonplace this season especially on head rigs, HUSSAR is the most popular  product  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 now in its third season.TRIAD is very effective on chickweed. 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

Growth stages in cereals are hugely influenced by day length. Now into the third week of May, the longer days are driving ear development, and with it ear emergence. The most advanced fields are at flag leaf emerging, GS37-39. Awns emerging, GS50 is only days away in these crops – once at this stage it will be too late to apply any growth regulator.  It is critical to assess crops now to check if a growth regulator is required.

In many cases the T1 fungicide may have only been applied in the last 10-14 days, with the T2 application not due for another couple of weeks yet. However to hold off and apply the growth regulator with the T2 fungicide will be too late for most crops, as in all likelihood the awns will be showing by this time.

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. 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.

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. Winter wheat crops are at varying growth stages

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.

 

Grassland

As fodder reserves are now almost depleted on many farms attention is now on getting as much grass into the clamp as possible. Where grass is still not ready for first cut there may still be the opportunity to treat docks and other problem weeds. DOXSTAR, PASTOR and FOREFRONT are all very safe to the grass. Losses in grass yield often go unnoticed because farming practice tends to focus on livestock output rather than the actual output of the grass. The productive capacity of grassland depends on a large number of factors but in the main is dependent upon the climate and the soil. Mild temperate weather with deep rich soils is the most favourable. Other factors such as the topography of the land, species mix, and sward damage can be important, but generally to a lesser extent.  Weed infestations can impact significantly on the yield and quality of grass for both grazing and cutting with trial work confirming a 10% weed infestation will cause a 10%yield loss. FOREFRONT is the most effective herbicide available to grassland farmers for the control of docks, chickweed, thistles, dandelions, nettles and buttercups. It is the longest lasting weed control product in grassland to date with a single well timed spray giving control up to 18 months so whilst it may appear expensive it really is good value for money.

 
 

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