New tool lifts canopy management potential

Photo of a man kneeling, smiling.

Nick Poole from the Foundation for Arable Research
says new tools to fight leaf diseases and respond to
crops’ nitrogen needs could be worth hundreds of
dollars a hectare to high-rainfall zone growers.

 PHOTO: Kellie Penfold

New tools to fight leaf diseases and respond to crops’ nitrogen needs have been developed for cereal growers in the high-rainfall zone (HRZ), following a three-year project by the Foundation for Arable Research.

The project’s leader, Nick Poole, says new guidelines for canopy management and disease control – including a simple ‘calculator’ – could be worth hundreds of dollars a hectare to HRZ growers.

“For example, our previous research gave confidence to cereal growers to delay nitrogen and fungicide decisions until stem elongation,” Mr Poole says.

“This project went to the next step to improve gross margins by using the crop canopy as an indicator for making better decisions once the crop reaches stem elongation.”

The project involved 39 trials and 10 workshops and has been summarised in a publication to be released later this year.

CANOPY MANAGEMENT

Trials across the southern grains region showed that the use of crop sensors to assess the need for top-dressed nitrogen at stem elongation have the potential to save up to $60/ha in fertiliser costs.

“Our trials showed a strong relationship between nitrogen uptake and sensor readings from late tillering to the third node, if appropriate test strips are used to calibrate the figures,” Mr Poole says.

“This relationship is particularly useful to assess the degree of nitrogen available to the crop in spring. Linked with crop models in the future, it is envisaged that crop sensors could enable growers to better visualise the growth of their crops.

Green leaf calculator
An output of the Foundation for Arable Research’s disease
and canopy management project is the ‘green leaf retention calculator’.
The calculator links fungicide decisions with soil water availability during
grain fill – a key factor in financial returns from fungicides.

The length of time a crop holds its green leaves during grain
filling affects its yield, as green leaves convert sunlight to carbohydrates,
which fill grains. If a crop has sufficient moisture, the length of time its
leaves stay green is influenced by nitrogen supply, leaf diseases
and extreme temperatures.

Nick Poole says experiments and model simulations show
the effect of leaf disease on green leaf duration is similar to the
effect of water stress: “So we have been able to adapt the
APSIM/Yield Prophet® model to simulate the relationship
between leaf area after flowering. We have also simulated the
potential effect of different disease levels under different
conditions of soil moisture,” he says.

“We have developed a simple calculator for growers to
compare the likelihood of green leaves being retained in
crops after flowering and their anticipated yields.

“The calculator paves the way for fungicide decision
making to be integrated into yield models, such as APSIM
[Yield Prophet®].”

The project also found that crop sensors can be employed
to determine the extent of green leaf retention during grain
fill using normalised difference vegetative index data.

Future research aims to quantify the effects of different
timings of infection and different variety resistance
ratings on leaf area.

“The use of crop sensors may have a greater role where nitrogen applications are split. The sensor can be used after the first top-dressing to determine whether a second application of nitrogen is warranted on parts of the paddock.”

The project also aimed to integrate canopy management with wide row spacing. Findings include:

  • an average six per cent yield penalty, but higher protein content, from wheat sown on 30-centimetre row spacing, compared with 20 or 22.5cm, in crops yielding above 5 tonnes/ha;
  • for crops yielding 2 to 3t/ha, row spacing had little effect on yields;
  • nitrogen requirements and optimal timing were the same, regardless of the row spacing; and
  • that ideally, growers should avoid planting seeds less than 2cm apart within a row when sowing with wide rows, due to competition between plants.

Trials in Tasmania also found for early-sown (March or April), long-season wheat, grazing before stem elongation prevented lodging and is more effective than other methods. However, in a wet spring, this was also associated with yield loss. The other factors found to reduce lodging were, in order of importance, variety choice, cutting sowing rates, applying plant growth regulators or delaying nitrogen.  

Barley was also studied. In Western Australian trials, the project revealed at least half of a barley crop’s nitrogen should be applied at sowing when soil nitrogen is below 75 kilograms/ha in the top 60cm. In contrast, top-dressing can wait until stem elongation for more fertile soils in the southern region.

DISEASE CONTROL STRATEGIES

Timing is everything when it comes to wheat and barley diseases.

Wheat stem rust

The research showed that growers choosing stem-rust-susceptible varieties should apply fungicides at the very early stages of the disease or before it is evident.

Sprays applied for stem rust beyond the late-milk stage are not cost effective.

Mr Poole says that, unlike stripe and leaf rusts, fungicide application to treat stem rust can be used later in the season and still secure financial returns. In addition, the effectiveness of fungicides against stem rust in wheat is more dependent on the rate and choice of product.

“Our trials showed that products used below the label rate were much less effective against stem rust than when used at the full rate. On average for a range of products, the low rate gave only 61 per cent stem rust control, while the high or label rate gave 87 per cent control.

“We found that formulated mixtures – such as Amistar Xtra®, Tilt Xtra® or Prosaro® – at label rates gave more than 90 per cent stem rust control. The active ingredient propiconazole [for example Tilt®] was less effective in the two years of trials, giving only 75 per cent control,” he says.

Wheat stripe rust

In guidelines developed for varieties with adult plant resistance (APR) to stripe rust, a fungicide may still be needed at the early stages of stem elongation to protect the top three leaves of the crop until its natural resistance steps in.

Barley

Powdery mildew and leaf rust in barley also came under the spotlight in southern WA. The project found two applications of newer fungicide mixtures, Prosaro® or Amistar Xtra®, gave the most cost-effective response in regions where these diseases are a problem. Further, powdery mildew is suspected of being less sensitive to older triazole fungicides, such as tebuconazole.

According to Mr Poole, the new stem rust control measures developed by the project could be worth $80/ha, while new guidelines to manage powdery mildew and leaf rust could be worth $50 to $100/ha in southern WA.

GROWER GUIDE

To obtain a copy of the guidelines

Image of cover of Advancing management of crop canopies research report

Advancing management of crop canopies
Nick Poole

Advancing the management of crop canopies: Keeping crops greener for longer developed from this project free phone

Ground Cover Direct 1800 11 00 44.

More information:

Nick Poole, Foundation for Arable Research (Australia),
03 5265 1290,
poolen@far.org.nz

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GRDC Project Code SFS00017

Region West, South, National, North