Spraying strategy options to avoid costly lodging in oilseed rape crops

A wet, mild autumn combined with strategies to overcome flea beetle could leave some crops at greater risk of lodging next year, which may benefit from an autumn growth regulator.

There is a greater risk as some farmers up seed rates above normal because of the flea beetle threat, says Adas senior research consultant Pete Berry.

“Some early crops following barley are also likely to be larger, as it has been wet enough for quick germination and good growth.

See also: How to plan a one-hit fungicide strategy for oilseed rape

BASF business development manager Clare Tucker also believes tackling flea beetle will increase lodging risk.

“With early drilling and more crops being planted at higher seed rates to try and foil cabbage stem flea beetle, if the pest doesn’t turn up in the expected numbers, we could be seeing some very advanced, larger crops this season,” she says.

But it’s not going to be a season where all crops are forward, those following late harvested wheat and further north will be less of a problem.

Key points

  • High cost of lodging
  • Some crops following barley at higher seed rate at risk
  • Spring treatments may be insufficient
  • New growth regulator option for this autumn
  • Economic benefits still to be quantified

In addition, Dr Berry believes the amount of residual soil nitrogen may be lower when following the high-yielding cereal crops seen this season, thereby, limiting growth in the autumn.

Cost of lodging

For those growers who have forward crops, Ms Tucker warns that lodging can prove costly.

This is due to less light getting into the canopy, restricting the supply of essential assimilates during the critical seed-fill period.

Dr Berry says that in his experience, severe lodging at early pod fill can reduce yields by as much as 50%, which is a high cost.

“We know how to manage big crops in the spring, by using a combination of delayed and reduced nitrogen [fertiliser applications] and growth regulators.

“And we know that if it is a very big crop, this is insufficient to get the canopy back to the optimum size. Therefore, farmers may need to do something in the autumn,” says Dr Berry.

The target is a growth area index of 3.5 at mid-flowering and the ideal canopy is more open with stronger lower branches and more light reaching these lower levels.

“We know that applying a growth regulator in the autumn has a noticeable effect on stem height and canopy size.”

However, he adds that the work hasn’t yet been done on quantifying the effect on yields and economic benefits.

“But he does see a potential role for an autumn application, given that spring tools are insufficient for very forward crops.

Extra option

Up to this year, growers had two possible options for use in the autumn with metconazole and tebconazole and from this autumn, there is a third option following the approval of Caryx (metconazole + mepiquat chloride) for autumn use.

Caryx was launched by BASF two springs ago, being a true growth regulator for spring use with greater growth regulation activity than a fungicide with growth regulatory properties.

“Autumn registration was granted on the premise that in some autumns where crops are advanced, a single spring application of a growth regulator may be insufficient to give full lodging control,” says Ms Tucker.

So how would this fit in with the existing oilseed rape fungicide programme?

The autumn label recommendation for Caryx is 0.7 litres/ha applied to forward crops at the four- to six-leaf stage.

“It is important not to let the crop get too big,” she warns.

“The usual window should be September and October when the crop is still actively growing.

Dr Berry adds: “This will coincide with early epidemics of phoma in crops, which occur following above average rainfall in August and September.”

Ms Tucker says that 0.7 litres/ha contains a 30% dose metconazole, so it will provide some protectant activity. “And the bigger plants in forward crops are going to be more tolerant of phoma.”

However, if 10% of plants have phoma spots, then she advises adding a 20% dose of difenoconazole or prothioconazole.

Looking at products, Dr Berry highlights that Caryx is a more powerful regulator. “Having two different actives means it will work in wider range of conditions.”

Both have different modes of action and temperature requirements, with metconazole being optimal at 12-18C while mepiquat is active down to 5C. This means the product can cope with variable autumn conditions.