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Crop Crack 8.05.10
By Wendy Fearon
The showery conditions over the last week have certainly helped all crops. The damp conditions will improve the performance of residual herbicides applied onto potato and vegetable crops. All spring cereal crops have now been drilled and most are well brairded. 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. Product choice will depend on the weed type and size present and crop growth stage.
Spring Cereals
Broad leaved wise, Sulfonyl-urea (SU) herbicides such as ALLYMAX 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 such as COMPITOX 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.
With IPU no longer available HUSSAR is the only product now available to treat AMG in spring crops, controlling this weed 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.
Wild Oats
Note that the performance of wild oat herbicides is adversely affected by other herbicides used on the crop. To avoid these antagonisms and possible damage to the crop, a minimum time interval must elapse between application of the BLW herbicide application and the wild oat herbicide application. The best option is to get the BLW treatment on as soon as possible so as to allow the maximum interval elapse for the wild oat treatment.
AXIAL gives excellent control of wild and tame oats in spring barley and spring wheat and has an excellent window of opportunity. Application should be held off until at least 6 weeks after drilling to ensure all wild oats have germinated. It can then be applied up to full flag-leaf of the crop and full flag leaf of the wild oatGS39, allowing a minimum of 21 days to have elapsed after application of the BLW herbicide. The wetter ADIGOR must be used in all situations along with the AXIAL.
Potatoes
Maincrop potatoes are currently being planted into ideal soil conditions right across the province. While planting conditions are excellent and the rainfall in recent days will be welcome, the return of a bit of heat will allow weeds to germinate quickly.
There are two types of herbicidal activity;
Contact herbicides which are those that must come into direct contact with the leaf of the target weed, so controlling all weeds that are emerged at the time of application – known as post emergent activity (post-em) and residual herbicides which move into the soil and prevent germination of the target weed before it emerges – known as pre-emergent activity (pre-em).
Most herbicides have only the one mode of activity; ie. a contact will have no effect on weeds not yet emerged, while most residuals will not control weeds already emerged. In addition the residuals need sufficient soil moisture to work properly and in dry conditions residuals will not perform well.
Contact products
RETRO is active on small grass & BLW it is very rainfast (15min) & can be
used when the crop has emerged. A wetter must always be added, specifically ACTIVATOR 90.
ROUNDUP ENERGY (glyphosate) – a new recommendation for 2010. Best on all grass types, esp AMG & good on BLW but application must precede crop emergence to avoid damage. TITUS is active on a range of BLW and AMG, also gives suppression of scutch but is very slow to work and is not approved for use on seed.
Because of the limitations of each of the contacts, all require the inclusion of a residual partner to maintain clean drills up to the time of the crop canopy closing the drills.
Residual products
DEFY is safe on all soil types and varieties but very poor on polygonums (redshank,
knotgrass, bindweed), fat-hen & field pansy. It cannot be used post-em of the crop.
AFALON (linuron) has a wide spectrum of weeds but the maximum rate is now limited to 600gm active per ha and at this rate does not give enough residual activity when used alone
SENCOREX gives excellent spectrum on pre-em BLW & AMG, and good contact ie post-em activity also, but can damage certain potato varieties, therefore soil type and varietal restrictions must be checked before use.
The efficacy of all residuals falls off when soils dry out. Any ridging up should be done before application of a residual, as any soil disturbance after application will adversely affect performance.
FALCON has a full recommendation for scutch control on ware potatoes. It will also give excellent control of perennial ryegrass, wild oats and volunteer cereals. If the crop is under drought or temperature stress when sprayed, transient yellowing may occur. For this reason its use is not approved on seed crops since these symptoms could be confused with viral disease.
Winter Cereals
Winter barley crops have improved greatly over the last week with fertiliser certainly working. Awns have begun to appear in some early drilled crops and all growth regulator should now be applied. All T1 treatments onto both barley and wheat should now be complete with some growers already planning to apply T2 onto winter barley.
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