Contribution of leaves to the yield of sunflowers - Willow Tree 2016-17


Research organisaton
Funding sources

Trial details


To quantify the contribution of different sunflower leaves to yield and oil quality by applying 12 leaf defoliation treatments.

Sunflowers are generally considered a minor crop in the northern grains region. However, they play an important role in providing a broadleaf summer crop rotation option. An individual sunflower plant produces on average 2000–6,000 cm2 of leaf area, which drives yield and oil content.

Identifying which leaves contribute most towards yield and oil content helps inform decisions around disease, pest and general crop management in sunflower crops. Whether it is because the crop is infected with a disease such as powdery mildew, or has insect damage e.g. loopers, the end result is a need for growers and advisors to know where and when to spend money in crop protection to achieve the best economic return on investment through maintaining green leaf area.

Key messages
  • Sunflower yields were greatly affected by the various defoliation treatments, ranging from 0.12 t/ha to 0.97 t/ha.
  • Reductions in yield, of between 55% and 82% compared with the control resulted from total leaf removal at all three of the targeted growth stages (budding, start of flowering and flowering completion) as well as removing two-thirds of the leaves at budding.
  • There was no negative effect on grain yield from removing the bottom third of leaves at budding or the start of flowering. Removing the bottom third of leaves at the start of flowering actually provided a slight yield advantage over the control treatment. The largest effect on plant height, head diameter and head arc length were caused by removing all leaves at the budding stage.
Lead research organisation Department of Primary Industries NSW
Host research organisation N/A
Trial funding source GRDC DAN00197
Trial funding source DPI NSW DAN00197
Related program Tactical agronomy for selected crops in the northern region (safflower, linseed, sunflower)

This experiment was part of the project Tactical agronomy for selected crops in the northern region (safflower, linseed, sunflower) (DAN00197), with joint investment by NSW DPI and GRDC. Thanks to Nuseed and Neil Weier for the supplying seed for the experiment. Technical assistance provided by Delphi Ramsden, Alice Bowler, Max Cloake and Jim Perfrement (NSW DPI) is gratefully acknowledged. Thanks to Joe Fleming, ‘Parraweena’, Willow Tree for hosting the experiment. Thanks to Neroli Graham for assistance with the statistical analysis.

Other trial partners Joe Fleming, ‘Parraweena’, Willow Tree
Download the trial report to view additional trial information


Crop type Oilseed: Sunflower
Treatment type(s)
  • Crop
Trial type Experimental
Trial design Unknown
Sow rate or Target density Not specified
Sowing machinery Not specified
Sow date 9 October 2016
Harvest date 24 February 2017
Plot size Not specified
Plot replication Not specified
Plot blocking Not specified
Plot randomisation Not specified
Paddock history Not specified
  • 150 kg/ha Gold N pre-sowing
  • 10 L/ha Amps Kickstart plus Petrik applied at sowing
Herbicide Not specified
Insecticide Not specified
Fungicide Not specified
Pesticide Not specified
Soil amelioration Not specified
Seed treatment Not specified
Inoculant Not specified
Tillage Not specified
Other trial notes

Crop type: Sunflower (Hybrid: Ausigold 62)

Starting soil water and rainfall:

The site was soil cored before sowing and found to have 130 mm of plant available water (PAW) to a depth of 1.2 m. Rainfall was recorded at the experiment site 


Plant height:

The height of five plants in each plot was measured before harvest, taken from ground level up to the point of attachment at the back of the head. The average plant height in the experiment was 141.7 cm. Removing all leaves at the budding stage had the greatest affect on plant height, at only 117.5 cm, a 25% reduction .

Head diameter and arc length

The head diameter and arc length of five plants in each plot were measured before harvest. Head diameter was measured across the back of the head and arc length across the front face of the head. The average head diameter was 15.9 cm across all treatments. Total leaf removal at budding had the largest impact on head diameter, reducing it to 3.6 cm. This was closely followed by removing 2/3 of the leaves at budding and removing all the leaves or 2/3 at the start of flowering 

The average arc length was 16.5 cm. There were significant differences between defoliation treatments. Removing all leaves at budding had the largest affect on arc length reducing it to 3.2 cm. Removing all leaves at the start of flowering and removing 2/3 of leaves at budding also significantly reduced the arc length to 10.4 cm and 7.3 cm respectively. There was no effect on arc length from all of the 1/3 leaf removal treatments compared with the control

Grain yield:

Harvested grain yield at 9% moisture ranged from 0.12 t/ha to 0.97 t/ha at this site. There was a large and significant effect from defoliation treatments on yield. The largest effects on yield resulted from removing all leaves at all three of the targeted growth stages (budding, start of flowering and flowering completion). Removing the top 2/3 of the leaves at budding resulted in a similar yield reduction as the total leaf removal treatments . Removing the bottom 1/3 of leaves at the start of flowering (R5.1) improved yield compared with the control. Removing the top 1/3 of leaves at budding, start of flowering or flowering completion did not affect yield compared with the control, neither did removing the bottom 1/3 of leaves at budding or removing 2/3 of leaves at the start of flowering or flowering completion 

Grain quality
Sub samples from each plot were collected at harvest and analysed for 1000 grain weight and test weight. Oil contents were not available at the time of publication.
The average 1000 grain weight in the experiment was 41.2 grams. Defoliation treatments did not significantly affect 1000 grain weight (data not shown).
The average hectolitre weight in the experiment was 35.6 kg/hL, which is well above the receival standard of 32 kg/hL (data not shown).

Download the trial report to view additional method/treatment information

Trial results Impact of defoliation treatments on sunflower plant structures

# Treatment 1
Plant height (cm) Head arc length (cm) Head diameter (cm)
1 Control - no leaves removed (0/3) 144.7 21.4 19.1
2 Budding - remove all leaves (3/3) 117.5 3.2 3.6
3 Budding - remove top 10 leaves (1/3) 146.8 17.6 18.1
4 Budding - remove top 20 leaves (2/3) 137.6 7.7 9.8
5 Budding - remove bottom 10 leaves (1/3) 152.5 22.2 19.6
6 Start of flowering - remove top 10 leaves (1/3) 146.6 19.4 18.1
7 Start of flowering - remove top 20 leaves (2/3) 132.9 16.9 17.1
8 Start of flowering - remove all leaves (3/3) 139.4 10.4 11.6
9 Start of flowering - remove bottom 10 leaves (1/3) 146.3 21.2 19.2
10 Flowering complete - remove top 10 leaves (1/3) 139.4 19.6 18.1
11 Flowering complete - remove top 20 leaves (2/3) 157.3 20.6 19.6
12 Flowering complete - remove all leaves (3/3) 138.9 17.6 17.5
LSD (P=0.05): 13.05 (P=0.05): 4.38 (P=0.05): 2.36

Head arc length cm


Head diameter cm


Plant height cm

Observed trial site soil information
Trial site soil testing
Site Depth Type pH EC P K N A OC CAT
Willow Tree, NSW 0 - 10cm 6.40 37.00 1.58
Willow Tree, NSW 10 - 30cm 6.70 9.00 1.00
Willow Tree, NSW 30 - 60cm 7.00 4.00 0.80
Willow Tree, NSW 60 - 90cm 7.80 10.00 0.64
Willow Tree, NSW 90 - 120cm 8.10 25.00 0.46
Soil conditions
Trial site Soil texture
Willow Tree, NSW Not specified
Derived trial site soil information
Australian Soil Classification Source
Trial site Soil order
Willow Tree, NSW Anthroposol
National soil grid Source
NOTE: National Soil Grid data is aggregated information for background information on the wider area
Actual soil values can vary significantly in a small area and the trial soil tests are the most relevant data where available

Soil properties



Willow Tree NSW 2016

Observed climate information
Rainfall avg ann (mm) 668.9mm
Rainfall trial gsr (mm) 639mm
Derived climate information
NOTE: Exact trial site locality unknown - Climate data may not be accurate
BOM Data source [] 0km proximity to trial site location


Some data on this site is sourced from the Bureau of Meteorology

SILO weather estimates sourced from
Jeffrey, S.J., Carter, J.O., Moodie, K.B. and Beswick, A.R. (2001). Using spatial interpolation to construct a comprehensive archive of Australian climate data , Environmental Modelling and Software, Vol 16/4, pp 309-330. DOI: 10.1016/S1364-8152(01)00008-1.

Trial report and links

2016 trial report