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CROP CRACK 04.10.08
By WENDY FEARON
Clarendon Agricare -Sowing Winter Crops
With most of this years’ harvest well through, growers will now turn their attention to sowing next years’ crop.
Aphids pose an ever-increasing problem to newly emerging plants. With a lot of damage done to both winter and spring crops this past season, aphid numbers remain high and will quickly move into new crops as these emerge. In this scenario any delay in applying an aphicide gives huge scope for the aphids to transmit Barley Yellow Dwarf Virus (BYDV) into the crop as it emerges. Remove the ‘green bridge’ – grassy stubbles and volunteers should be sprayed off, buried 7days later, and then at least 2 weeks should elapse before drilling the new crop.
Slugs will also be a major problem to crops this autumn with the wet conditions allowing this pest to thrive. Typical damage is hollowing of the seed and irregular shredding of the leaves as the plants emerge. Huge improvements to crop establishments have been consistently achieved where the slug bait is mixed in and drilled with the seed.
Farmers have until June 2009 to use any product containing IPU, depending on availability they can still use products such as PANTHER, ENCORE, FIELDGARD etc.
Whilst stocks of PANTHER & ENCORE are now exhausted, growers can still apply the same actives at identical dose rates using similar products still available, good control of AMG remains the key issue; when not properly controlled this weed is a major robber of yield. IPU gave pre and post emergent control. Its weakness (which has now led to its demise) was its solubility making it prone to leaching so its residual activity tended to fall off quite quickly in a wet season, allowing AMG and chickweed to come through later.
All the alternative actives for AMG control have however narrower spray windows than IPU, therefore timing is more critical to obtain a good result.
Flufenacet one of the actives in Crystal offers the widest window for good AMG control early on – 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) present in Othello and Pacifica 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 must be used late winter – early spring. (In addition these actives can only be used on winter wheat, not winter barley or winter oats.)
Pendimethalin (PDM) & trifluralin are also very active on AMG, but pre-emergent only. They are much less soluble than IPU, so persist for longer in the soil. These 2 actives also have a much wider BLW spectrum than IPU.
Diflufenican (DFF) is another widely used active in the autumn and is present in Koala 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. IPU also gave good activity on some BLWs, notably chickweed, mayweed and groundsel. Whilst PDM and DFF are good on chickweed & DFF good on mayweed, neither are effective on groundsel – control of this weed came solely from the IPU. All the SUs give very good control of this weed but none of the autumn residuals (once IPU is gone) are effective, therefore this weed will have to be controlled once it is all emerged, either Late winter or early spring with OTHELLO, or with another SU later on along with the cleaver control.
Be aware that the length of persistency of any herbicide product that has residual activity is inversely related to soil temperature – the lower the temperature the longer the duration of its persistency; therefore as soils cool over the coming weeks so product performance will improve. Soil acting herbicides also require adequate soil moisture to work, but their performance will fall off in a wet winter when the actives may be leached away before the crop canopy is big enough to prevent a late weed infestation. With all crops, especially those earlier drilled being at risk of BYDV infection once emerging, the aphicide should be applied once the crop has one full leaf along with the herbicide.
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