Course: Lodging control in cereals | Last Updates: 7th October 2015
Damage resulting from lodging can be severe – yield losses have been shown to be as high as 75% in affected crops.
In severe lodging years, which occur every 3-4 years in the UK, 10-15% of the cereal area will suffer, with losses in those patches estimated on average at 25%.
Quality also drops off in a lodged crop, with Hagberg hit hardest, threatening milling premiums. A lodged crop also takes longer to dry and longer to combine, and the mat of laid straw left behind can be difficult to cultivate into a decent seed-bed.
What is lodging?
If a wheat or barley plant carries an ear that either its stem or root cannot hold up, the crop will lodge.
Stem lodging is where the stem or shoot buckles above ground level. Root lodging will occur where the plant has insufficient anchorage. In both cases, wind acts on the shoots after ear emergence to create a leverage force that will cause the crop to lean or lay flat on the ground. The size of the force is determined by wind speed, area of the ear and height of the crop.
What factors affect lodging?
Variety, sowing date, residual nitrogen and plant density all have a large impact on lodging risk.
Variety choice is the first route to control lodging risk, and one with a resistance score of 6 or below on the HGCA Recommended List usually requires careful management. But the other three factors can have a huge influence on a crop’s overall resistance to lodging (see table, below).
The more shoots a crop has, the more competition there is for limited resources. This means there will be thinner, weaker stems, placed closer together which are more prone to buckling. The result is greater leverage exerted on the anchorage system which also has less potential to form a wide root plate. So root lodging, in particular, is more likely to occur where plant density has been mismanaged.
Seed-bed can also influence lodging risk. Roll after drilling or in the spring before growth stage 30, as a light and fluffy soil provides poor anchorage. Crops in a peat soil, with its weak ability to bind and inherent high fertility, are most prone to lodging. But soil strength is affected most by rainfall – just 7mm can wet up the 40mm anchorage zone and weaken resistance to lodging.
What effect does nitrogen have?
Nitrogen is the input that will have the biggest bearing on whether your crop will remain standing. Residual soil nitrogen and early applications are the most significant factors; high levels early on encourage more tillering, so stems will be weaker and longer, putting more leverage on the root.
It’s worth measuring soil nitrogen supply in the early spring, particularly if the supply is likely to be high, such as a field that has recently been ploughed out of grass or has a history of manuring. Recent research has now quantified the effect of nitrogen applications on lodging risk (see table, left). This shows applying 60kg/ha of N more than the RB209 recommended rate at GS31 reduces stem and root lodging score by one point.
Tailoring timing and rates to the individual crop is crucial to getting the balance right. It is vital to delay applications to crops which have a large canopy coming out of winter.
What role does crop canopy play?
Many of your spring agronomy decisions that relate to lodging can be based on an early assessment of crop canopy. Canopy size at GS30 and 31 has been found to have a strong correlation with lodging risk.
This is measured by a crop’s green area index (GAI) – the total surface area of green material/sq m of crop. The best way to assess this is to compare your crop with photos of a known canopy size. A new web-based Canopy Assessment Tool has been introduced that allows you to upload digital photographs of your crop, and this will automatically tell you the GAI (www.pgrplus.basf.com).
At GS30, each 0.5 unit increase in GAI above 1.25 effectively reduces the variety lodging resistance score by one point. This equates to about 50-60% of ground cover before stem extension starts. At GS31 the critical GAI is 1.75 – around two-thirds of the ground will be covered.
How are PGRs best used?
In valuable crops and those with a high lodging risk, plant growth regulators (PGR) are a cost-effective defence against lodging.
There are two main groups: Those that inhibit gibberellic acid biosynthesis and ethylene-releasing compounds. The first group includes chlormequat, Meteor (chlormequat + imazaquin), Moddus (trinexapac-ethyl) and Canopy (prohexadione-calcium + mepiquat chloride).
Best applied before third node detectable, these work by reducing cell elongation, which shortens stem extension and reduces height. They work best when the crop is actively growing and splitting the dose can boost effectiveness.
These PGRs are relatively inexpensive and give a linear response, so are often cost-effective.
Cerone (2-chloroethylphosphonic acid) and Terpal (includes mepiquat) are examples of ethylene producers, which are applied later and affect cell division in upper internodes. They work by shortening the stem and making it stiffer. The latest application date for these is GS39, but avoid applying excessive rates when the crop is drought-stressed.
The two groups have an additive effect, so if used sequentially to high risk crops they will significantly enhance standing power. But there is great potential for them to be used more effectively through growers making an accurate assessment of canopy at the start of the season. Perhaps 90% of UK crops receive a base dose of chlormequat or equivalent. Many crops don’t need an application, while others warrant a more robust programme.
Do stem and root-based diseases have an influence?
Research has shown a moderate infection of eyespot (lesions girdling more than half the circumference of the stem) at GS83-87 reduces stem strength by 17% and lodging resistance by one point. A severe infection can knock lodging resistance by as much as three points.
Take-all doesn’t present such a serious lodging risk. But recent research, carried out by ADAS and funded by BASF, has shown that a seed treatment with growth regulatory activity can help. Treatment tends to deepen the crown of the plant, improving anchorage by 10% and resistance score by one point.
Variety choice is the first route to controlling lodging risk
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