CROP CRACK - 13.10.07
By WENDY FEARON
Clarendon Agricare - Winter Cereal Technical Update

Growers have taken advantage of the improved ground conditions and a lot of field work has been done over the last number of weeks. Almost all of the winter barley is now drilled, and a good start made on the wheat. With the improved economics for cereals it looks very likely we will see a significant increase in acres drilled this autumn as long as the weather allows. Farmers should be aware that early drilling of winter wheat dramatically increases the likelihood of a Take-all yield reduction in wheat following cereal situations and should therefore use an appropriate seed treatment.

Slugs will be a major threat to crops this autumn with the wet summer months allowing this pest to thrive. Typical damage is hollowing of the seed and irregular shredding of the leaves as the plants emerge. 

Aphids also pose a threat to crops this autumn, particularly in early sown fields. With relatively mild temperatures 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.

For years IPU has been one of our most important herbicides in the autumn, being the foundation for controlling annual meadow-grass in wheat and barley. However because of traces of the active continuing to be found in drinking water in parts of England, its approval for use in the UK is being withdrawn. As of 30th Sept 2007, manufacturers are no longer allowed to market any products containing IPU. The trade are allowed to supply growers up until 30th Sept 2008, and growers are allowed to use the products up until 30th June 2009. In addition its maximum rate has been reduced to 1500gm/ha – 3.0lt/ha of straight product eg. FIELDGARD.

For this season FIELDGARD, ENCORE and PANTHER will continue to be freely available and will form the basis of weed-control programs for this autumn. In addition, limited quantities of CRYSTAL, will be available.

Good control of AMG remains the key issue, when not properly controlled this weed is a major robber of yield. Timing is critical as good results will only be achieved when treated before the beginning of tillering. The best results are obtained when treated pre- emergent or 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 well after emergence.

IPU gives pre and post emergent control. Its weakness (which has now led to its demise) is its solubility making it prone to leaching so its residual activity falls off quite quickly in a wet season, allowing AMG and chickweed to come through later. Pendamethalin & trifluralin are also very active on AMG, but are much less soluble than IPU, so active for longer. These 2 actives also have a much wider BLW spectrum than IPU, therefore adding these to IPU will prolong control of the AMG and widen out the broad-leaved weed (BLW) activity. Diflufenican is another partner for IPU as in PANTHER. This will control larger emerged BLW than the other actives, but has no AMG activity whatsoever.

Flufenacet (CRYSTAL) offers the widest window of AMG control and 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 peri-emergence.

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.

Slugs

The wet summer has allowed slugs thrive, limiting natural mortality associated with drier conditions. Cereals being drilled into leys, potato beds or grassy stubble are at greatest risk. Loose unconsolidated seed-beds are most at risk, where slugs can move up to and down from the soil surface as moisture conditions dictate. Typical damage is hollowing of the seed and irregular shredding of the emerging leaves; consequently slug control needs to be considered right at time of drilling.

Slug pellets should be ad-mixed with the seed at drilling, or applied as soon after sowing as possible.

Barley Yellow Dwarf Virus (BYDV)

This disease is carried by aphids and passed on to the crop when they feed on the young plants. Once infected, the disease cannot be controlled. Therefore control is aimed at prevention of crop infection, controlling the aphids with insecticide at the correct time.

As seen in spring barley this season, infection was widespread. Aphids feeding on these crops as well as other host crops including grass ensure the aphid population is well loaded with the virus, and the mild conditions so far means aphid activity and migrations are high, and mortality low. This all adds up to all autumn crops being as risk of infection, especially those emerging early, which may need a second treatment to keep the aphids out until the colder weather takes over.

An application of insecticide should be made as soon as the crop has 1 fully emerged leaf. Delaying application will leave the crop unprotected at its most critical stage. Like the residual herbicides, product persistency is very dependant on temperature, improving as temperatures fall.