26 February 1999

DODGINGTHELODGING RISK

Control of lodging is essential for a cereal crop to reach

its yield and quality potential. John Tearle investigates

the main lodging risk factors in cereals and what can

be done to lessen the chance of a flat crop

LODGING has as much, or more, to do with the state of the crop than summer weather. So assessing crop condition in early spring should be the cornerstone of any lodging prevention strategy, says consultant John Spink of ADAS Rosemaund. "If weather was the most important factor then the whole crop would lodge rather than parts of a field or one field and not another."

Cereal crops lodge as a result of three factors:

&#8226 Leverage of the above ground part of the crop.

&#8226 Stem base strength.

&#8226 Anchorage strength.

"These can all be influenced by the way we manage the crop," says Mr Spink.

"Leverage force, determined mainly by the centre of gravity, the springiness of the stem and the number of shoots per plant, can be increased by early drilling in wheat.

"Stem strength is affected by the diameter of the stem, the thickness of the stem wall and the strength of the stem wall material. High soil nitrogen levels or too much nitrogen too early in the spring produce thicker crop canopies with narrow stem diameters and thin stem walls, reducing stem strength," he says.

"The anchorage of the crop is determined by the diameter and depth of the structural portion of the crown roots, and also by the soil type and structure of the surface layer of soil. High seed rates can decrease crown root diameter and crop anchorage."

The lodging risk of varieties is currently judged by the standing power score given in the UK recommended list of cereal varieties. "This is a good guide, but varieties differ in the reasons for which they are likely to lodge," says Mr Spink. "A short variety may have a particularly poor crown root system and be more likely to lodge than a taller variety that has good anchorage and a strong stem. Knowledge of why a particular variety may have a high lodging risk would allow it to be grown in such a way that the weakness is reduced."

In the knowledge of work carried out at ADAS Rosemaund, John Stevenson of ADAS Wolverhampton has some clear messages for this spring. "We have two situations this year. Many wheat crops were drilled late last autumn and many are thin due to slug damage and poor establishment. Here the risk of lodging is likely to be lower."

But risks may be greater in better established crops.

"High rainfall over the autumn/winter period has reduced root structure and made predicting soil nitrogen reserves difficult. I would recommend a soil mineral nitrogen sample to help establish accurate nitrogen timing and rates particularly where pig or poultry manure has been applied."

Considering those factors, plus others which influence lodging, should be the basis for pgr planning. Risk assessments devised by ADAS can help (see tables).

"Unless lodging risk is particularly low most wheat crops should receive some chlormequat as the cost effectiveness of chlormequat on winter wheat is well established," Mr Stevenson says. "Chlormequat is best applied during warm days and night with high humidity. Adjust or Meteor may be more effective under cold conditions." &#42

ADAS lodging risk assess

Variety

Insert UK recommended list "standing power" score ?

Site lodging history

None +1

Slight 0

Some in most years -1

Severe in most years -3

Drilling date

Early September -3

Mid-September -2

Late September -1

Early to mid-October 0

Mid-October to mid-November +1

After mid-November +2

Spring plant population

Less than 200 per sq m +1

200-250 per sq m 0

250-350 per sq m -1

More than 350 per sq m -2

Yield potential

Less than 7t/ha +1

7-8t/ha 0

8-10t/ha -1

More than 10t/ha -2

Potential market

Feed 0

Bread or seed -1

Nitrogen and timing

MAFF booklet RB209 nitrogen rates but later than recommended timing +1

RB209 rates and timing 0

40kg/ha above RB209 rates before growth stage 30 -2

40kg/ha above RB209 rates after growth stage 30 -1

More than 40kg/ha above RB209 rates at growth stage 30/31 -2

40kg/ha above RB209 rates after growth stage 32 0

Soils with unknown nitrogen residue -1

Using ADAS soil mineral nitrogen service 0

Action:

If final score is greater than 7: Low risk. No treatment necessary.

5-7: Medium risk. 1.75-2.5 litres/ha chlormequat (645gai/l) applied at growth stage 30 (Adjust or Meteor may be more effective in cold conditions).

3-4: High risk. 1.75 litres/ha chlormequat applied at growth stage 25 to 30 followed by 0.75 litres/ha at growth stage 30 to 31. Or 1.75 litres/ha chlormequat at growth stage 30 to 31 followed by 1.5 litres/ha Terpal at growth stage 32 to 37 or 0.5 litres/ha Cerone at growth stage 37 to 45.

1-2: Very high risk. 1.75 litres/ha chlormequat applied at growth stage 25 to 30 followed by 0.75 litres/ha at growth stage 30 to 31. Followed by 1.5-2 litres/ha Terpal at growth stage 32 to 37 or 0.5 litres/ha Cerone at growth stage 37 to 45 or 0.2-0.3 litres/ha Moddus up to growth stage 39.

Source: ADAS