❚ High lodging risk for OSR and cereals
❚ Nitrogen and growth regulators vital
❚ Assess OSR green area index and cereal rooting strength
A warm, wet autumn combined with a shift to earlier drilling has resulted in many cereal and oilseed rape crops being much further ahead than expected this season, with big, lush plants.
This brings an increased risk of lodging and associated yield losses, which can be particularly high in oilseed rape, with estimates of up to £183/ha.
However, there is a risk that growers overlook lodging on the back of a low-risk year as they face increased pressure from grassweeds, diseases and pests, prompting experts to warn managing lodging risk needs to be a higher priority.
A key consideration, according to Harper Adams University lodging expert Mitch Crook, is to be proactive rather than reactive. “Last year the need for plant growth regulators (PGRs), and more nitrogen splits was much less apparent, but this season is going to be very different with so many forward crops.”
Lodging costs the UK oilseed rape industry up to £137m a year, according to an aerial survey carried out by BASF and ADAS in 2012.
The survey also found that an average 35% of the oilseed rape area was lodged, often in the centre of the field where it was less visible to the farmer and thus underestimated.
Cereal crops meanwhile can also suffer significant yield losses as a result of lodging. Wet weather and nitrogen are the major catalysts and with an increasingly unpredictable climate, preparation this spring will be key.
Making changes to fertiliser programmes and using PGRs will be at the forefront of spring management decisions for growers.
Although there are many forward crops, record-breaking wheat farmer, Tim Lamyman, proved that nitrogen is still crucial when pushing for yield managing risk with a little but often approach in 2013.
This could well be the key to success this season as well, so for growers understanding the risks and how to manage them will hold the key to achieving maximum yields in crops that remain standing.
❚ Many oilseed rape crops are sitting proud in the field with some of the largest rape plants senior research consultant at ADAS Pete Berry has ever seen at this time of the year, because of the mild weather.
Lodging is one of the key threats to oilseed rape yields and early management will provide growers with the best chance to overcome it along with any subsequent disease threats.
Canopy management will also play an important role this year with yield differences of more than 0.4t/ha seen if managed correctly. The optimum canopy growers need to aim for will be erect and will look fairly sparse with the leaves still there after flowering. There will also be a reasonable amount of green leaf area.
In a survey carried out in 2012, it was estimated that lodging could have reduced the national average yield by between 0.25 and 0.61t/ha, resulting in losses of between £75/ha and £183ha (with rape at £300/t).
These findings also showed nearly every field suffered some sort of lodging, and with yield reductions of 16-50%, it is a grossly underestimated problem, says Dr Berry.
To ensure fungicide and fertiliser programmes result in short plants with strong lateral branching, nitrogen applications will need to be delayed and a growth regulator product will be essential.
“Growers need to be thinking about lodging in terms of when they time their first nitrogen split. If you have got a big canopy already then you should be looking at delaying the first nitrogen split to reduce the size of the canopy,” explains Dr Berry.
The first step for growers will be assessing the green area index (GAI) of the crop, which will be vital in gauging when PGRs and nitrogen need to be applied.
There are a number of options available in order to measure the GAI of a crop including BASF’s iPhone app, which takes a picture of the crop and gives a reading.
“If you have got a larger canopy than that, then you are better off chopping it off an and weighing it,” says Dr Berry.
“Basically chop a 1m/sq area of the crop and weigh it. Then every 1kg equates to 0.8 GAI, so for example if you have got 4kg of crop you simply work it out by multiplying 0.8 by four gives you a GAI of 3.2,” he explains.
Many farmers will be going with three splits, with the first split going on late February/early March, depending on what part of the country you are in, says Dr Berry.
“I think if you have got a big canopy, anything above a GAI of 1.5 you should be looking at reducing that first split. If you have got a very big canopy above 2, then you might even consider missing out the first split altogether.”
An average nitrogen programme of 200kg/ha for a canopy with a GAI of 1.0 may be split by putting 40kg/ha on at the early timing in late February early March, followed by 100kg/ha at green bud and 60kg/ha at yellow bud, says Dr Berry.
“Crops with large canopies might see growers put as little as 100-150kg of nitrogen on. So you might keep the middle split at 100kg or even less and keep the final split at yellow bud, which is really for yield, at anything between 60-30kg/ha.
“If you have got a yield potential of more than 3.5t/ha then for each 0.5t above that you are looking at applying an extra 30kg at yellow bud timing.”
The key timing this year will be the first application, says Dr Berry, who stresses not putting too much on too early will be pivotal in preventing lodging.
Meanwhile, BASF agronomy manager Clare Tucker notes that although nitrogen may need to be used sparingly this year, recent wet weather may have reduced nitrogen through leaching, meaning there will be less soil reserves.
Crops that have a GAI of 0.8 or greater will require a PGR, according to Ms Tucker, who recommends 0.8 litres/ha of metconazole (Sunorg Pro) once the crop is visibly growing.
Work carried by ADAS has shown metconazole is useful at manipulating crop canopies, diverting growth from leaf biomass into seed and oil yield.
Spring applications have been shown to increase root length density by 25% at a 40-100cm depth.
“This will normally be about April at yellow bud and it will help maximise canopy effects and seeds/sq m for yield. There will also be the benefit of sclerotinia control.”
At the yellow-bud stage the crop is still only 40% of its final height, so there is still a lot of height reduction you can do and you can also change the balance of branching, so as well as reducing the height and reducing the lodging risk, says Ms Tucker.
Tebuconazole-based products also offers growers a growth regulating fungicide, which has performed well in trials, adds Dr Berry.
Forward crops with a GAI of more than 2.0 may require a product with PGR activity at late green bud stage or stem extension, according to Ms Tucker.
“The key thing for yield in rape is seeds/sq m and you only get this when you get good contribution from the lower branches.
“You reduce the dominance of the main raceme of the rape plant so light can penetrate down to the lower branches, allowing the pods that start to form to get some light and start to photosynthesize – preventing them from aborting.”
The co-formulation of mepiquat chloride + metconazole (Caryx) will be another option available to growers this year having been launched in the UK last spring.
Ms Tucker highlights the newcomer will give consistent results early on when conditions are colder with it available to go on from growth stage 31-59.
“The mepiquate chloride is more active at regulating growth at lower temperatures of about 5C, where as metconazole works well between 12-18C.”
The product has three key effects on the plant; helping promote a better canopy, protects against lodging and promotes rooting.
“Generally 1 litre/ha is common and proved successful in trials, but if you have got a very forward crop and a tall variety you may want to use 1.4 litres/ha.
If you have got a crop with a GAI of just over 0.8 you might just use 0.7 litres/ha.”
Straight metconazole would normally go on at yellow bud at 0.6 to 0.8 litres/ha, but if you wanted to do a split programme and use metconazole early on, use 0.4 litres/ha with another follow up spray.
❚ Lodging can be equally devastating in cereals affecting yield and quality and 2014 could prove to be a high- risk season, which is why Dr Berry believes using a growth regulator will be particularly cost effective this spring.
Severe lodging occurs ever three to four years in the UK with 10-15% of the cereal area suffering with losses in the affected areas of about 25%. The latest figures suggest this costs £108m of yield in a bad year, with the additional losses of that accompany lodging.
Dr Berry highlights crops going for milling are hit the hardest, with a steep decrease in the Hagberg falling number and with increased disease pressures.
“A lodged crop can also take longer to dry and combine and lead to problems with subsequent cultivations, so managing it is key.”
Dr Crook, has carried out extensive research into lodging and believes a better understanding will help growers prepare in high risk years. “Managing lodging problems will largely come down to agronomy and variety. Ultimately, what is causing the lodging is the weight of the ear and the height of the plant.
“Half of the dry weight is in the ear which shows how wheat plants are elaborate structures. Heavy ears mean higher yields, but also increase the chance of lodging.”
There are two main types of lodging in cereals; stem-based lodging and root-based lodging, with the latter effecting a larger majority of crops.
“Many growers automatically assume that it is stem-base lodging they are seeing, however, root-based lodging is far more common. If you look at the crop the stems are usually intact,” explains Dr Crook.
Root lodging can happen anytime after ear emergence so when the crop becomes heavy it begins to fall over which is normally close to harvest.
“The key risk is when it is wet, although wind can play a role, which will expose any insufficient anchorage systems.”
With the roots developed by Easter, the key thing for growers this year will be to assess the root structures in this month in order to prevent lodging.
“This involves digging a plant up and seeing how robust the roots are now. Typically if you have got about five main roots that are 5mm plus and have some rigidity to them, then you are reducing the risk of lodging.
“There is a huge difference in how strong the soil is between being dry and saturated, just as a consequence of how wet it has been.” Dr Crook suggests rainfall decreases the soil strength by 1,000%, whereas the rainfall itself only effects the lodging risk marginally.
Syngenta’s Jason Tatnell says that like oilseed rape crops, there are also a lot of cereal crops that are a high risk of lodging that will require a PGR programme tailored to variety.
“They are going to produce a lot of foliar biomass this spring which will need to be managed and there are plenty of options to help deal with the problem, but will require careful management.”
The HGCA lodging guide will play a big role in helping growers understand their crop and the risk of lodging, according to Mr Tatnell. When assessing a variety’s lodging risks, identify its standing power on the Recommended List.
Soil nitrogen, sowing date and plants/sq are at the forefront of this and aid the decisions a farmer will make in the spring.
Prior to any decision on PGRs or nitrogen, growers should consider increasing root anchorage by rolling crops before GS30.
PGRs in cereals
There are two main groups of PGRs in cereals that work in different ways. The most common sort which includes Moddus (trinexapac-ethyl), inhibit gibberellic acid biosynthesis.
These work by reducing cell elongation, which shortens stem extension and reduces the height of the plant. They work best when the crop is actively growing and splitting the dose can boost effectiveness, according to Dr Berry.
Cerone (ethephon) and Terpal (chloroethylphosphonic acid + mepiquat) are examples of the second group of PGRs, which work through ethylene-releasing compounds which shorten the stem and making it stiffer.
“Growers must take into account that this year is a high-risk lodging year and using some sort of a PGR focusing on improving root strength and helping shorten the plant,” says Mr Tatnell.
Trinexapac-ethyl and chlormequat will be instrumental in preventing lodging, according to Mr Tatnell who suggests extensive trial work has shown benefits against all the main factors in lodging.
“They shorten the crop height as well as improving rooting and strengthening stem bases in wheat. Another consideration is the benefit they will give you against eyespot.
“To target both roots and stems in winter wheat and barley you should be looking at applying trinexapac-ethyl up to growth stage 30, followed by another application of Moddus + chlormequat at growth stage 31-32.”
Dr Berry says a programme based on two applications around early stem extension and a later application at growth stage 37 should be considered this season.
“With Moddus + chlormequat at early stem extension, you get a bigger effect if you split the application at growth stage 30 and 31.”
A later application of ethephon + mepiquat chloride may be important in high-risk lodging situations.
Nitrogen will have one of the biggest bearings on whether your crop will remain standing with residual soil nitrogen and early applications 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,” says Dr Berry.
He suggests three splits of nitrogen will suit most growers, however, the first one will be key.
“It is going to be important to assess the size of the crop and the number of tillers the crops have got, in February and at the start of stem extension.
“If you have got 1,000-1,200/sq m, it might be necessary to delay or avoid the first split of 40kg to minimise the lodging risk.”
Milling wheat growers may wish to go for an extra application, however, it is second wheats that will require extra management to help counter the risk of take all.
“For second wheat, it is more important to have that early split on because you need it to combat the take all, so it is possibly more important to have that on to help the crop tolerate the take all pathogen.”