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Crop Crack 23.05.09
By Wendy Fearon
In the last crop crack I spoke about cereal acreage yet to be drilled and in many cases this has not changed with the weather having provided little or no opportunity to get on with fieldwork. Any cereals yet to be drilled will most likely be used for wholecrop.Everything has been badly affected and crops were actually going backwards.
There has been very little silage cut to date and potato and vegetable growers are away behind. Many crops have begun to yellow due to wet spots, compacted headlands – and those crops which were rolled. The waterlogged soil becomes anaerobic (i.e. no oxygen available) so halting the soil microbes from making nitrogen and other nutrients available to the crop, hence the yellowing.
There are some incidences where crops are showing signs of purpling almost like that seen with phosphate deficiency and may be confused as this. Cold and wet conditions can cause temporary symptoms which will correct themselves when the weather improves.
SPRING CEREALS
In situations where the crop is temporarily under stress due to water logging or poor fertility, a broad-spectrum trace-element mix along with key macronutrients is very beneficial to top up the plant’s nutrient requirement that is not being adequately provided for in the short term by root uptake alone, especially during phases of rapid growth. Application of a balanced and rapidly available source of macro & micronutrients at this key time will minimise the adverse effects of restricted soil nutrient uptake.
CEREAL PLUS supplies 3.7%Mn, 1.5%Mg, 1.8%Cu, and 0.6% Zn in the most rapidly available form to plant through the leaf and also supplies high levels of Nitrogen and Sulphur.Potash deficiency is also showing up in many spring barley crops with pale green yellow tips being the first symptom.Deficency is most likely on light sandy soils or in crops grown following intensive grassland.
To minimise the effects of competition on the crop and optimise the level of weed-control, herbicide application should be carried out at the earliest opportunity, once all the weeds have emerged but are still small, and before they begin to compete with the crop for nutrients and light. With plenty of soil moisture and low soil temperatures, since drilling, weeds are not coming through as rapidly as expected but chickweed is beginning to choke out you young plants and must be sprayed as soon as possible.
Product choice will depend on the weed type and size present and the crop growth stage. Broad leaved wise, Sulfonyl-urea (SU) herbicides will likely be the starting point, controlling a wide range of weeds and very safe to the crop. Options are ALLY MAX covering a wide spectrum of BLW with the MAX formulation giving improved control of polygonums & other BLW over the old ALLY formulation. HARMONY SX controls a wide range of BLW at sizes larger than any other SU.
However they must always be tank-mixed with another BLW herbicide to control SU resistant weeds (chickweed) and those weeds not controlled by the SU’s (cleavers, fumitory& fat-hen). Ideal partners are COMPITOX controlling (chickweed, fat-hen, fumitory), OXYTRIL CM controlling (field-pansy, red dead-nettle and speedwells) and STARANE XL/MINSTREL for chickweed and cleavers.
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.
The two most important diseases of spring barley in NI continue to be Rhynchosporium and Powdery Mildew.The persistent rainfall since drilling has meant disease pressure is extremely high but care must be taken when spraying those crops under stress. The T1 should be applied during late tillering up to just before 1st node (GS25-30), and can be timed to coincide with the main BLW herbicide application. T2 should be timed to follow up about 4 weeks later with flag leaf extending through to booting (GS38-42), applying a growth regulator then also if required.
Chlorothalonil in the mix will give good control of Ramularia when used preventatively.
An insecticide should be included as aphids are now present on many crops.
WINTER BARLEY
Most winter crops are now beginning to struggle .The pressing issue now is getting sprays applied at the correct timing with the persistent rain and deteriorating ground conditions preventing any fieldwork at present.
The main aim of the T2 treatment is to protect the top three leaves as up to 80% of the yield is derived from these leaves, and foliar disease not controlled effectively at this time will hasten the senescence of these leaves during grain fill, and therefore affect yield and grain quality. Where the crop is relatively clean, the T2 fungicide spray should be applied 4-5 weeks after the T1 application date.
In winter barley this should be applied during booting to ear emergence, GS45-49, and be robust enough to protect the upper leaves and ear through to the end of the season.
Rhyncho has advanced rapidly with the recent spell of wet weather. Mildew and Net Blotch are also present in some varieties, but levels of infection remain low.
Ramularia (sometimes known as Leaf Spot) is also beginning to show in many crops, with newer varieties showing much more sensitivity to this late developing disease. It tends to show late in the season usually after booting, symptoms very similar to manganese deficiency.
The triazoles form the core of the fungicide mix, with prothioconazole, epoxiconazole and flusilazole being most robust for Rhyncho, both preventative & curative. Chlorothalonil is most effective for Ramularia when used preventatively, helping to maintain green leaf area when used along with a triazole.
WINTER WHEAT
Most crops are now moving through the stages of stem elongation with more forward crops at flag leaf. Septoria tritici is present in most crops at variable levels depending on T1 timing but with recent weather; expect levels to rise if fungicide rates and timings are not correct.
As the flag leaf will be emerging in most crops within the next week or two it is the key time to apply the T2 treatment. Of all fungicide treatments, T2 has the greatest impact and response in terms of grain yield and quality, keeping the top three leaves clean and the ear as it emerges. The dose rate applied must be sufficiently robust to ensure long term protection of the flag leaf plus eradicate disease already present on the lower two leaves that also contribute to yield.
Epoxiconazole or prothioconazole are key to this treatment, other triazoles are no longer sufficiently effective alone to provide effective control of Septoria. Both these triazoles are also the strongest on Rusts, particularly where curative control is required.
Chlorothalonil continues to perform on Septoria at this timing also and should be part of the mix. I hope by the time this article goes to press this very gloomy period has passed and a bit of decent weather has arrived.
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