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Crop Crack 25.10.10
By Wendy Fearon
Winter wheat continues to be sown with good soil conditions. Cereal aphids have continued to fly into crops and breeding colonies have been found on most crops. Crops should be inspected and an insecticide applied if necessary. We have been fortunate over the last few weeks with regard to slugs. The drier conditions have left it difficult for them to feed. Later sown wheat takes longer to emerge and consequently the more time there is for slugs to inflict damage to the crop. For this reason avoid sowing wheat too deep, as this prolongs even further the time needed to get to GS12.The weather is offering a very mixed bag and time is of the essence with regard to autumn herbicide application.
There is a good choice of autumn herbicide products available but most of these must go on early. Temperatures have not yet dropped significantly and autumn herbicides work much better in cooler temperatures.
Chlorotoluron (CTU) is of the same family of chemistry as IPU, and has identical mode of action and very similar spectrum of weeds controlled, including AMG, chickweed, mayweed & groundsel. Its’ principal limitation is its potential to scorch; certain varieties of winter barley & winter wheat are not tolerant to CTU, so can only be used on named varieties (check approved variety list). In addition, only use when the seed is well covered and the crop is not under any stress.
Flufenacet offers the widest window for good AMG control – it is very residual so will remain active for an extended period after application, controlling from pre-emergent through to beginning of tillering. Ideal timing is very early post-emergent – a new definition for this timing is now being used, peri-emergence, meaning around the time of emergence as distinct from some time after emergence.
Iodosulfuron & mesosulfuron (both sulphonyl-ureas, SUs) will control AMG well into mid-tillering, but have contact activity only, therefore requiring all the AMG to be emerged for control to be satisfactory, so really can only be used from early spring onwards. (In addition these actives can only be used on winter wheat, not winter barley or winter oats.)
Pendimethalin (PDM) is also very active on AMG, but pre-emergent only. It is much less soluble than IPU, so persists for longer in the soil. PDM also has a much wider BLW spectrum than IPU.
Diflufenican (DFF) is another widely used active in the autumn; it is residual and has a wide spectrum of BLWs controlled, taking out larger emerged BLWs than many other residuals, but has no AMG activity whatsoever.
Flufenacet will be the mainstay of AMG control in the 2010-2011 crops. This active also gives good activity on brome and perennial rye-grass when used at its maximum rate. ICE contains flufenacet and pendimethalin and can be used on all varieties of winter barley & wheat.
BUCKLER contains CTU & DFF. Where the variety list allows this product should be tank-mixed with ICE. Its inclusion will extend the spray-window of ICE, allowing larger weeds to be controlled than if the ICE were used alone. The CTU will also bring groundsel activity to the mix, whilst the DFF will broaden the spectrum of emerged BLW controlled, including chickweed & mayweed. Only use when the seed is well covered, and not subject to stress as a result of waterlogging or frost. Cloddy seedbeds will lead to poor results from residual herbicides especially at low water volumes.
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