A simple visual lodging risk guide to assist with decision making on Plant Growth Regulators

Author: Nick Poole & Tracey Wylie (FAR Australia), Allan Peake (CSIRO) & Matt Gardner (AMPS) | Date: 07 Mar 2017

Take home messages

  • Irrigation increases crop canopy biomass and supports higher yield potential; both however put greater stress on stem strength and the anchorage of the plant in the soil, leading to increased risk of lodging.
  • Two of the biggest determinants of lodging (other than weather conditions during grain fill) in irrigated wheat crops are the cultivar lodging resistance rating and the inherent fertility (N supply) of the paddock.
  • Background N supply to the crop can be “visualised” and quantified with reference to NDVI readouts or canopy photos comparing N deficient or N Rich strips to the remainder of the paddock.
  • PGR input and N management at stem elongation represent the last opportunity to reduce lodging risk with management matched to lodging as defined by the visual appearance of the crop and knowledge of cultivar standing power under irrigation.
  • These recommendations were generated from experiments and farm monitoring on vertosol soil types in the ‘old’ northern region (Northern NSW and QLD), and caution should be taken applying them outside of these districts.

Background

A small component of the “Better Irrigated Wheat Agronomy” project (CSA00039) led by CSIRO has been tasked with producing a simple visual guide to lodging risk. As part of the project, FAR Australia has been working on the linkages between the visual appearance of the crop at stem elongation and its subsequent propensity to lodge.

Like fungicides, managing PGR’s is about risk management, adjusting the level of ‘insurance’ purchased against the potential risk of crop lodging. As with fungicides, one doesn’t know whether the PGR insurance will pay until the end of the season, since the agrichemicals have to be applied at critical development stages before all of the climatic factors have been expressed. 

The problem

Irrigation increases yield potential and lodging risk!

Lodging occurs regularly in northern region irrigated wheat crops. It reduces yield and quality as well as increasing harvesting costs. Lodging is the result of compounding factors. Irrigation increases crop canopy biomass and supports higher yield potential; both however put greater stress on stem strength and the anchorage of the plant in the soil, leading to increased risk of lodging. Therefore the irrigation that gives rise to higher yield potential, when combined with unsettled windy weather also increases lodging risk, particularly during grain fill.

How can we get clearer indication of lodging risk in an irrigated wheat crop?

With regards to crop management there are two categories of lodging risk factors, those that the grower can control and those they cannot. Of those factors that the grower has some control over, it is clear from our research results that some have a greater influence on lodging risk than others. From this work and from feedback from advisers, the following table gives an indication of some the key agronomic factors associated with lodging in irrigated crops (Table 1).

Table 1. Factors associated with lodging risk deduced from trials run in the project (Generally higher star ratings confer greater influence over lodging risk)

Factors not under the growers control

Lodging risk rating

Factors under the growers control

Lodging risk rating

1. Inherent  fertility – high fertility that is long standing for that paddock in the rotation

*****

1. Cultivars’ resistance to lodging – Cereal cultivars have different root architecture and stem strengths that increase or decrease lodging risk

*****

2. Windy and wet weather (ear emergence to harvest)

*****

2. Irrigation (1) – Irrigation timing in relation to expected weather conditions is a key factor in lodging risk (2) total irrigation applied increases yield potential and hence lodging risk

*****

3. Total N rate applied – Higher N rates increase lodging risk particularly superimposed on high inherent fertility

***(*)

4. Nitrogen (N) timing - Earlier (at sowing) nitrogen application can increase lodging risk, particularly if inherent fertility is already high.

***

5. Sowing date – Earlier sowing dates, particularly combined with high seed rates can increase lodging risk.

**

6. Seeding rate – Higher seed rates can increase lodging particularly combined with earlier sowing and inherent fertility.

**

These factors have different weightings and different consequences for lodging risk depending on seasonal environmental conditions, irrigation however is a very large driver of lodging risk since the size of the crop canopy and grain yields supported by the crop canopy are much larger than those achieved on dryland.

In interviews with regional agronomists other factors having influence on crop lodging were brought forward, including row orientation, basal P levels both inherent and applied giving vigorous early growth, seed depth and consolidation ensuring good plant anchorage to prevent root lodging.

Management actions to prevent lodging

Influence of cultivar on lodging risk

One of the most important factors in preventing lodging is the selection of a lodging resistant cultivar which are traditionally characterised by stiffer straw strengths and better root anchorage. The majority of germplasm screening in the northern region has been conducted under dryland conditions but the project has also been able to rank the standing power of some of the current cultivars and conduct screening of early generation lines to assess yield potential and standing power under irrigated farming systems.  Of the current cultivars that have been tested, Table 2 shows the most and least lodging resistant cultivars when grown under irrigated scenarios.

Therefore one of the simplest ways of reducing lodging risk in an irrigated wheat crop is to select a lodging resistant cultivar.

Table 2. Preliminary lodging ratings for varieties as rated using preliminary results from the 2014-2016 trials of the Better Irrigated Wheat Agronomy Project.  Varieties sown early in their sowing window may not achieve the level of lodging resistance indicated. Yield potential, grain quality, maturity and disease resistance among these varieties is variable and growers should consider aspects of varietal performance when selecting a variety.

Lodging Rating

R-MR

MR

MR-MS

MS

MS-S

S

Variety

Sentinel

Cobra

Suntop

Wallup

Crusader

Trojan

Livingston

Merinda

Dart

Condo**

Kiora**

Bellaroi

Caparoi

Mitch

Kennedy

Lancer

Sunmate**

Spitfire

Aurora*

Lillaroi*

EGA Gregory

Suntime*

Flanker*

Orion

R-MR = Resistant to Moderately Resistant
MR = Moderately Resistant
MR-MS = Moderately Resistant to Moderately Susceptible
MS- Moderately Susceptible
MS-S = Moderately Susceptible to Susceptible
S = Susceptible

* = Preliminary rating based on one year of trial data
** = Preliminary rating based on two years of trial data

Other management options that can be adopted to reduce your lodging risk

Other factors that can reduce lodging risk but have less impact than cultivar standing power are the key components of crop canopy management. Those factors under the control of the grower and adviser can be split into two categories:

a) Measures that can be adopted at sowing

  1. Review seeding rate >higher seeding rates increase lodging risk, particularly when they are combined with earlier sowing - plant by seed number to achieve target plant populations of approximately 100 -125 plants/m2 with higher target where sowing is delayed.
  2. Seed depth Ensure that seed is planted into a consolidated seed furrow at 30-40mm depth combined with the correct plant population
  3. Review nitrogen (N) quantities at sowing Soil + fertiliser N at sowing is recommended to be 70-90 kg /ha in order to minimise excessive vegetative growth during tillering.

b) GS30 (Pseudo stem erect – start of stem elongation)

  1. Review N quantity and timing at the start of stem elongation  At the start of stem elongation the crop canopy can visually signal its fertility status and therefore its propensity to lodge given conducive weather conditions.

  2. Plant Growth Regulator (PGR) application  If cultivar lodging risk suggests a higher risk of lodging consider PGR application in the late tillering to second node window GS25-32.

"Visualising" lodging risk

How can paddock fertility and lodging risk be visualised?

One of the most influential factors giving rise to lodging in an irrigated wheat crop is the inherent fertility of the paddock. This fertility and the associated propensity of the following crops to lodge “can be visualised” in the crop canopy at the start of stem elongation and was widely experienced in 2008 in the northern region when large quantities of sowing N was applied to soils with high levels of available nitrogen, and extremely thick canopies were produced.The link between crop density in terms of shoot number and Green Area Index (GAI) are used in lodging risk tools in Europe. 

In Australia, agronomists regularly assess crops visually using their experience to judge the vigour and crop canopy size as a surrogate for fertility and associated N supply at different development stages. The issue in estimating inherent fertility is complicated by the fact that northern Australian crops routinely receive N fertiliser at sowing, which can mask the visual indicators of inherent fertility in the crop.  This is much less of an issue in Europe since crops are not fertilised with large amounts of N at sowing, so crop canopy images in early spring at GS30-31 are more indicative of the background N mineralisation and the inherent fertility of the paddock. This is where an “old technique” for assessing soil nitrogen availability can be a good guide to assessing lodging risk and the appropriate level of PGR management.

In order to visualise paddock fertility and associated lodging risk (independent of N fertiliser already applied), four to five N rich or N deficient strips can be set up in the paddock at planting. This is where N is either excluded (if large quantities of N are being applied at sowing), or added (100-200kg N/ha), to four or five small areas of the paddock if no N is being applied to the commercial crop. These N strip areas needn’t be large, perhaps the size of trial plot or the width of the sowing rig with no N applied. The visual difference between these N deficient or N rich strips can then be compared visually to the remainder of the paddock in the spring at GS30-31 when remaining N and PGR inputs are considered.

Where fertility is very high, there will be little or no difference between the N rich/deficient strips and remainder of the paddock when assessed in the spring. In contrast where visual differences between the N rich/deficient strips and the paddock are pronounced, the fertility will be lower. Since high inherent paddock fertility has such a pronounced effect on lodging risk and irrigation serves to increase that risk, crop canopy visual appearance during stem elongation (GS30-39) is a key determinant of lodging risk and therefore also a useful predictor of the likely need for an application of Plant Growth Regulators (PGRs). The scale of this visual difference can be assessed at its simplest by visual observations of the agronomist. However it’s also possible to quantify the difference using readouts from a hand held GreenSeeker or by using a mobile phone photo.

Using a hand held GreenSeeker® to quantify lodging risk

The following table (Table 3) sets out three arbitrary categories of soil fertility on the basis of crop canopy appearance (recorded in northern region crops) at GS30-31 (visual difference between N rich strips or N deficient strips set up at sowing and the remainder of the paddock), as quantified with a GreenSeeker®. By dividing the NDVI representing the higher N status whether it be the paddock or the N Rich strip, by the No N strip or unfertilised paddock surround, gives the adviser the response index. For example 0.84 NDVI for the paddock divided by 0.83 NDVI for the N deficient strip set up at sowing, gives a NDVI response index of 0.84/0.83 = 1.012.  Below three arbitrary response indices ranges have been put forward to help estimate lodging risk and subsequent PGR input when combined with cultivar lodging resistance ratings grown under irrigation with yield potential of 8-10t/ha. 

Table 3. Different lodging risk scenarios based on NDVI response Index from N rich or N deficient strips set up at sowing in paddock scenarios of different fertility.Clearly the highest risk scenarios for lodging are where high inherent fertility (NDVI index at approximately 1.0), poor cultivar standing power and additional N applied at sowing combine.

Table 3. Different lodging risk scenarios based on NDVI response Index from N rich or N deficient strips set up at sowing in paddock scenarios of different fertility.Clearly the highest risk scenarios for lodging are where high inherent fertility (NDVI index at approximately 1.0), poor cultivar standing power and additional N applied at sowing combine.

Using mobile phone photos to quantify inherent fertility and potential lodging risk

Mobile phone photos can also be used to quantify the difference between N rich strips or N deficient strips set up at sowing and the remainder of the paddock. The link between crop density and lodging is used by online European websites that use mobile phone photos to quantify lodging risk. An example of such a website is the BASF CAT online which uses a mobile phone image to quantify Green Area Index (GAI), shoot number and subsequent lodging risk when combined with knowledge of the cultivar. 

http://www.agricentre.basf.co.uk/agroportal/uk/en/tools/website_tools/gai_cereals_cat_online/cat_online.html

Although this website is very specific to the UK in terms of parameters entered e.g. calendar date, location and cultivar it can still be used to quantify the relative (rather than absolute) differences between two mobile phone images in just the same way as NDVI readouts can be compared. The difference is that instead of using NDVI units to quantify the difference in canopy appearance, the photos are compared in terms of GAI units and shoot number, which can then be ratioed just as the NDVI readouts in Table 3 to generate the degree of difference. The only proviso with using such a website is to ensure that the assumed surrogate details provided are the same for both images uploaded.

To show how this website uses these images to generate a lodging risk prediction based on canopy structure, Figure 1 shows a simple comparison from the Liverpool Plains comparing images of irrigated wheat crops at similar growth stages GS31 in two different rotation positions.

Figure 1.  Irrigated wheat grown on the Liverpool Plains on the left a) cv Ventura following Sorghum GS31 (NDVI 0.50) and on the right b) cv Sentinel following canola GS31 (NDVI 0.69)

Figure 1. Irrigated wheat grown on the Liverpool Plains on the left a) cv Ventura following Sorghum GS31 (NDVI 0.50) and on the right b) cv Sentinel following canola GS31 (NDVI 0.69)

If image (a) were attributed the status of a weaker strawed cultivar (rated 5 for resistance to lodging) with 8t/ha yield potential the lodging resistance score would be 7 (1-9 scale where 1 has the highest potential risk of lodging). Conversely set with the same yield potential and using the image on the right the lodging resistance score decreases from 7 to 3 indicating a significant increase in lodging risk. Even without the website being adapted for Australian wheat cultivars lodging risk tools such as this give an indication of how crop canopy density (influenced by inherent fertility) relates to lodging risk. Using the same images but with a more lodging resistant cultivar (rated 8) increased the lodging resistance score to 9 (image a) and 5 (image b) respectively (Table 4).

Table 4. Lodging resistance score attributed to images uploaded to CAT online (1-9 scale 1 low lodging risk resistance – high risk, 9 high lodging resistance risk – low risk) at 8t/ha yield potential

Lodging resistance score (1 – 9 scale)

Image a) above

Image b) above

Lodging resistant cultivar

9

5

Lodging susceptible cultivar

7

3

Matching potential lodging risk to PGR insurance

Whilst there are other management actions that can be adopted to prevent potential lodging risk at stem elongation concerning N management (already discussed), there is also the potential to investigate PGR input. PGRs are very similar to fungicides in that they are insurance inputs for a potential risk that may not eventuate, but complicate matters as they can be associated with both positive and negative yield responses. Negative yield responses from PGR’s frequently occur when dryland crops encounter water or heat stress later in the season following application. In other circumstances, when lodging doesn’t occur and results are neutral. Clearly PGRs help reduce subsequent crop lodging in irrigated crops and this has been shown in the project, but it should be emphasised that adjustment of other crop canopy parameters can be just as important, cultivar standing power, reducing planting populations and delaying N application. Whilst irrigation increases lodging risk it does at least remove the potential for the more adverse effects of these products encountered in dryland crops. In fact the issue can be that under irrigation current PGR labels do not provide sufficient lodging prevention since labels have been generated with respect to dryland cropping. However there are clear differences in PGR performance that can be matched to label recommendations and potential lodging risk. 

AMPS Research conducted some excellent field research on the interaction between PGR treatments and durum wheat yields in 2016. The data suggested that mixtures of PGRs trinexapac ethyl (Moddus Evo®) & an experimental PGR were more successful than applications of a single active ingredient such as trinexapac alone. The data also illustrated that yield increases could be generated in the near absence of lodging with irrigated crops and that there would be merit in researching PGR sequences for higher risk scenarios in irrigated crops (Figure 2a & 2b) for which there is currently no label approval in Australia.  It should be noted that this experimental trial work included an application of Moddus Evo at GS25, when the earliest application on the approved Moddus Evo label is at GS30.

Figure 2a & 2b. Influence of PGR treatment (product & timing) on harvest lodging and final yield in the durum wheats AGT 043 (1a) and Bellaroi (bb).

Figure 2a & 2b. Influence of PGR treatment (product & timing) on harvest lodging and final yield in the durum wheats AGT 043 (1a) and Bellaroi (bb).

Figure 2a & 2b. Influence of PGR treatment (product & timing) on harvest lodging and final yield in the durum wheats AGT 043 (1a) and Bellaroi (bb).

The following label rates allow different levels of PGR insurance to be adopted for different levels of ldoging risk to be covered with different levels of insurance (Table 5 & 6).

Table 5. Potential PGR and N management at GS30-32 to take account of visual differences (and cultivar lodging resistance)  in potential lodging risk.

High lodging risk

Intermediate lodging risk

Low lodging risk

1. PGR management

Consider applying PGRs at higher rate or as label mixture (trinexapac ethyl & chlormequat chloride) applied at GS30-GS31.

Consider applying a PGR treatment at GS30-31.

(lower end of the rate ranges)

No PGR

Review the need for a PGR based on cultivar lodging rating and N applied to date.

2. N Rate and timing

Consider reducing overall N dose planned and splitting the N application remaining between GS31 and GS33-39.

Apply the majority of the remaining N at GS31.

Apply the majority of N as soon as possible if sampling strip is representative of the paddock.

N.B. Consult with your agronomist with regard to exact PGR products and timings (see table below)

Table 6. PGR’s approved for use in wheat

Product (active ingredient)

Rates approved for wheat (mL/ha)

Concn

Gibberellin

inhibitor

Active applied (gai/ha)

Zadoks

Growth stage

Single Active Products

Stabilan® 750SL (chlormequat chloride)*

500 - 1300

582g/L

Yes

291 - 757

GS25-35

Cycocel® 750 A (chlormequat chloride)*

500 - 1300

582g/L

Yes

291 - 757

GS25-31

Errex 750 (chlormequat chloride)*

500 - 1300

582g/L

Yes

291 - 757

GS25-31

Moddus Evo® (trinexapac-ethyl)

300 - 400

250g/L

Yes

75 - 100

GS30-32

Mixtures

Errex 750 + Moddus Evo®

1000 - 1300

+ 200

Yes

582-757 + 50

GS30-32

*PLEASE NOTE CYCOCEL 750A has no label approval for use in QLD or Northern Territory, ERREX 750 has no label approval for use in QLD or Northern Territory & STABILAN has no label approval for use in Northern Territory.

In conclusion, PGRs represent an insurance premium which the adviser does not know will pay until the end of the season, since these agrichemicals have to be applied at critical development stages before all of the environmental factors have been expressed. Visualising the crop canopy at early stem elongation and quantifying its inherent N supply enables the adviser to better match potential lodging risk with PGR and N management at this important development stage.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, and the authors would like to thank them for their continued support. We also thank farm and technical staff at the DAFQ Emerald Research Farm, CSIRO Toowoomba, the CSIRO Gatton Farm, and the University of Sydney’s Plant Breeding Institute (Narrabri) for their assistance in managing these trials, along with Angus Murchison of Spring Ridge for hosting some of the trials.

Further reading (available from the GRDC website at www.grdc.com.au)

Fact Sheet (Northern Region): ‘Reducing lodging risk in irrigated wheat’

GRDC Goondiwindi Update Paper (2012) by Peake et al. “Agronomy for high yielding cereal environments: varieties, agronomic strategies and case studies

GRDC Goondiwindi Update Paper (2014) by Peake et al. “Beyond 8 t/ha: varieties and agronomy for maximising irrigated wheat yields in the northern region

GRDC Goondiwindi Update Paper (2015) by Peake et al. “Irrigated wheat agronomy x variety trials: 2014 Trial Update

GRDC Goondiwindi Update Paper (2016) by Peake et al. “The effect of sowing date, variety choice and N application timing on lodging risk and yield of irrigated wheat

Contact details

Dr Allan Peake (Project leader)
CSIRO Agriculture, 203 Tor St, Toowoomba
Ph: (07) 4688 1137
Email: allan.peake@csiro.au

Nick Poole
FAR Australia, 23 High St, Inverleigh, VIC
Email: nick.poole@far.org.nz

Varieties displaying this symbol are protected under the Plant Breeders Rights Act 1994.

® Registered trademark