Friday, March 22, 2019

Give serious thought to spring spray programme

March 5, 2019 by  
Filed under Crops

An increasingly limited armoury means crop protection needs proper planning, says Richard Overthrow.

A relatively benign start to spring  tempted many into some early field work, be it drilling or top-dressing. For those who haven’t started yet, it’s not too late; ideally first nitrogen and sulphur doses will be on by mid March, and spring crop drilling by the end of the month.

As ever, spring linseed and rape should wait until next month anyway.

Once the first nitrogen doses are finished the final splits can be applied to oilseed rape towards the end of the month and it is these doses that may need adjusting in response to crop canopy size.

Few of the large canopy crops remained that way into spring so nitrogen management should be straightforward as a result. Second or main nitrogen doses to winter cereals should wait until April, unless urea is used as this can be applied sooner if required.

T0 fungicides

Later this month, T0 fungicide treatments for cereals will need some thought. Winter wheat crops will be due a treatment at the end of this month or early next, but all should be examined for yellow rust and any residual winter mildew as these will influence planning.

All crops will have similar levels of septoria so treatment for this will have to be guided by varietal resistance though some chlorothalonil would be a cheap insurance treatment. Chlorothalonil will be sufficient for septoria, with a triazole or strobilurin included for rust. This treatment is ideally applied three to four weeks before the T1 (leaf 3) treatment.

Winter barley crops may need T0 sprays applied this month though other than winter mildew as discussed previously, disease levels have been low so far. The T1 is typically applied in early April so assess any T0 requirement with this in mind.

Oilseed rape

Spring disease control in oilseed rape is a difficult area these days. Both light leaf spot and sclerotinia have been scarce in recent years and if these don’t appear then there is little reason to treat.

Light leaf spot can be assessed – possibly by incubating leaves to bring out any infection – and a stem extension fungicide applied if it is present. Disease resistance ratings in the variety concerned will also help with this.

But sclerotinia treatment is always prophylactic and the true extent of the disease isn’t known until close to harvest. This means flowering sprays need to be routine for nearly all crops, and these will be due sometime next month.

Growth regulators

Soon chlormequat-based growth regulators will be due on winter cereals, often with a T0 fungicide. Chlormequat is a routine treatment for nearly all winter wheat crops and increasingly so with barley.

In wheat, chlormequat contributes significantly to a lodging control programme and may be all that’s needed for stiff wheat varieties on light soils, or any late sown crop. These first treatments should be applied around GS30-31.

For barley, GS30 is usually the latest growth stage approved, and these treatments should be routinely followed-up later. Oats will also benefit from routine chlormequat treatment – where contracts allow – though this is usually applied around GS32 which is likely to be some way off yet.

March should also provide the final opportunities for late applications of grass weed herbicides such as Atlantis, Broadway Star etc. Good growing conditions for weeds and reasonable soil moisture – with target weeds still small – is ideal and less likely in April.

If pea or spring bean crops have been sown check carefully as they emerge in case weevils move in. If damage is seen it may be sufficient to hold crops back so a pyrethroid spray should be applied.

All spring crops will be prone to attention from birds so again monitor between sowing and emergence.

Richard Overthrow is a regional agronomist with NIAB TAG, the UK’s largest independent agronomy organisation with several research centres in the Midlands. For more details, call 01223 342495.

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