Arable: Agronomy Update - South West

Article taken from the Farmers Guide


Oilseed rape crops are coming out of the winter in good shape in most parts of Wiltshire and further afield. Apart from some areas that suffered from slug and pigeon damage, most crops are looking pretty even which will help simplify input timings over the next few weeks.

Pollen beetle numbers are likely to start building in oilseed rape crops following the onset of warmer weather and in some crops may reach threshold levels before flowering.

Numbers started to increase in mid-March and will need monitoring closely. Thresholds vary according to plant density-for crops with 30-50 plants/m2 it's 18 beetles/plant, for crops with 50-70 plants/m2 it's 11 beetles/plant.

Crops should be monitored when the weather is dry and warm, above 15°C, when beetles feed on green or yellow buds. Threshold numbers are relatively high, so accurate monitoring is required to ensure treatment is justified.

It is also worth bearing in mind that once crops start to flower this foe becomes an ally as it helps to pollinate crops. Certainly, no crop should be sprayed once it has started flowering.

Pyrethroids were the chemical of choice, but resistance has spread, meaning control often relies upon products such as Biscaya (thiacloprid) and Rumo (indoxacarb). Check for resistance status in your area before spraying, either online or through local contacts.

Galileo (picoxystrobin) Recital (fluopyram + prothioconazole) are my products of choice when it comes to sclerotinia control. Both offer good levels of control and provide additional crop greening benefits that help to build crop yield. I recommend applying in at least 200-litres/ha of water with Roller, a specialist adjuvant that helps increase coverage of stems.

I always advise an early/mid-flower spray, as fungicides are protectant, so it is vital to get chemical onto the stems before a rain event combines with petal fall. A follow-up application at late flowering should be considered if the weather remains catchy.

Maize pre-ems

Maize drilling will soon be underway so we need to plan for the all-important pre-emergence herbicide. Young maize plants are surprisingly intolerant of competition, and given that the number of grain sites is fixed by the six-leaf stage it is important to keep them growing unrestricted from the beginning.

As well as the obvious effect of competition for nutrients and sunlight, maize that is competing with weeds also suffers from elongated stems and shallower roots, both of which make the crop more susceptible to lodging. Early removal of weeds will encourage 360° growth.

Depending on weed spectrum, straight pendimethalin, Wing P (pendimethalin + dimethenamid-P) or Dual Gold (S-metolachlor) will all do a good job. Adding Remix, a chain hydrocarbon adjuvant, helps the chemical bindto the soil, it in the top layer to provide more persistent  and effective control.

Weeds will also need controlling in grassland. Leystar (clopyralid + florasulam + fluroxypyr) at 1-litre/ha is as good a choice as any and will control most problem broad-leaved weeds including chickweed, seedling docks and thistles. Triad (tribenuron­methyl) + Headland Spruce (2,4-DB) is another option if clover is present.

On established grassland, Pas +Tor (clopyralid + fluroxypyr + triclopyr) will take out troublesome weeds such as docks, nettles and thistles. These need to be actively growing for optimum control, so it is worth waiting for a warm settled spell if possible.

Where clover is present in established leys, Pinnacle (thifensulfuron-methyl) + 2.4-DB should be used.

 

Esme Shephard is an agronomist with Agrovista, base in Wiltshire (esme.shephard@ agrovista.co.uk)

 

04 April 2017

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