BENEFITS OF DESICCATION | CROP-TOP, DESICCATE, HARVEST OR MANURE? |
TIMING OF DESICCATION | CROP-TOPPING
SOUTHERN
SEPTEMBER 2018
SECTION 11
CROP DESICCATION/
SPRAY OUT
CHICKPEA1 CRoP DeSICCATIon/SPRAY oUT
seCtIon 11 CHICKPEA
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Crop desiccation/spray out
Key messages
• Chickpea often matures unevenly and require herbicides to ripen more evenly.
• Desiccation assists production by: taking out late weeds such as thistles which
can stain the seed, allowing for earlier harvesting which lessens the weather risk
at harvest and browning out green stems which can gum up knives in headers.
• The correct timing for desiccation is when 80–85% of the seeds in the pod have
turned yellow and are firm and the remaining 15–20% have yellow ‘beaks’ on the
seed or are starting to turn colour.
• A high water rate is advised to get coverage if using a contact herbicid\
e.
• After desiccation, plants become more brittle, so it is advised not to
delay harvesting.
11.1.1 Benefits of desiccation
Desiccation is the strategic termination of crop growth using herbicides. Desiccation
is an established technique to improve the rotational fit, benefits and profitability
of pulse crops. Desiccation provides important benefits such as reducing weed
seed-set, allowing faster harvest and improving grain quality, all leading to improved
profitability in pulses.
Desiccation prepares the pulse crop for harvesting by removing moisture from
plants and late maturing areas of the paddock. Desiccation is an aid to a timely
harvest, particularly where uneven ripening occurs across a paddock, and is now a
common practice in lentil and chickpea. Desiccation enables a timely harvest to avoid
weather damage.
Crop topping is a form of desiccation, but timing, products and rates differ from
desiccation. Desiccation is based on the crop stage close to maturity. The timing
of crop topping is based on the stage of development of weed seeds. Different
chemicals and rates are used. See Sections 11.3.1 and 11.4.
Application timing is based on the crop when the grain is 75–90% mature, to avoid
reducing the quality of the harvested grain. Windrowing can be considered similar to
desiccation in timing and benefits to harvest. Windrowing may be considered as an
alternative to desiccation. The timing of windrowing is similar to desiccation.
1
Desiccating a crop overcomes problems with green weeds at harvest and improves
harvest efficiency by eliminating many of the problems associated with green stems
and gum build-up, such as uneven feeding and drum chokes. Minimising these
problems enables drum speeds to be reduced in many cases, with a reduction in
cracked or damaged grain. It allows harvesting of a crop that will not naturally shut
down due to high soil moisture, and stops chickpeas reshooting and reflowering after
pre-harvest rain, and makes crops with uneven maturity more uniform, allowing earlier
harvesting.
2
While desiccation is often not necessary under very hot conditions where the crop
is under terminal moisture stress, it can be a very useful harvest management tool in
situations where:
• There has been rain during grainfill and the crop is uneven in maturity. Chickpea
are very indeterminate and will continue to flower and set up pods late in
the season. Crop maturity tends to be very uneven and slow in situations of
reasonable moisture supply.
1 Pulse Australia (2015) Desiccation and crop-topping in pulses. Pulse Australia, Australian Pulse Bulletin, http://www.pulseaus.com.au/
growing-pulses/publications/desiccation-and-croptopping
2 QLD DAFF (2012) Chickpea—harvesting and storage. https://www.daf.qld.gov.au/plants/field-crops-and-pastures/broadacre-fie...
chickpeas/harvesting-and-storage
F A Q
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• Pod-set has been very uneven due to agronomic factors such as low plant
population, poor Helicoverpa management, uneven plant establishment in some
deep-sown crops, wheel tracks through crops etc.
• There is a problem with actively growing weeds in the crop.
In these situations, desiccation is a valuable management tool for maximising yield
and quality through early harvesting. It also improves harvest efficiency by eliminating
many of the problems associated with putting green, sappy plant material through
the header, i.e. uneven intake and drum chokes. Minimising these problems enables
drum speeds to be reduced, with less likelihood of cracking grain.
3
11.2 Crop-top, desiccate, harvest or manure?
All pulse growers face the decision between crop-topping, desiccation, harvesting
or manuring, and their decision is dictated by weed pressures, weed type and the
nitrogen demands of the rotation.
11.2.1 When weeds are not the priority
Option 1
Management: natural maturation and grain harvest.
Goal: to maximise grain yield and profit while at the same time providing
rotational benefits.
Method: This is the most traditional and widespread practice for cultivating pulses in
NSW and is based on well-developed agronomy and crop management strategies
from sowing through to harvest. This option assumes weeds are fully managed by
conventional rotation and herbicides.
Option 2
Management: brown manuring.
Goal: to maximise N
2 fixation, N-benefit and to conserve soil moisture.
Method: The amount of N
2 fixed is linked closely to dry matter (DM) production of
the legume, therefore ‘manure’ the weed-free pulse close to its maximum DM. For a
typical Morgan PSE 23 (long-season) field pea crop sown at Wagga Wagga, NSW, in
late May, this would mean desiccating around the end of October.
11.2.2 When weeds are the priority, particularly if
herbicide resistance exists
Option 1
Management: brown manuring.
Goal: total control of weeds including herbicide resistance, and to fix some N and
conserve soil moisture.
Method: It is imperative to desiccate the crop at or before the milky dough stage
of the targeted weed. This often coincides with the flat pod stage of the pulse and
inevitably falls well short of the crop’s peak DM. At this stage the crop is growing
at its maximum rate (about 80–100 kg DM/ha/day), so the amount of N fixed will be
proportionally reduced according to its growth stage at desiccation. This cost is non-
negotiable and essential to ensure complete weed control.
3 B O’Mara, S Belfield, G Cumming (2007) Chickpea harvest and seed stora\
ge. Pulse Australia, www.pulseaus.com.au/storage/app/
media/crops/2007_Chickpea-Harvest-Storage.pdf
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Option 2
Management: crop-topping/desiccation followed by grain harvest, although this may
not be an option available to chickpea because of later crop maturity compared with
the weed seeds.
Goal: to maximise grain yield and profit while at the same time providing rotational
benefits of preventing weed seed set.
Method: This is the ‘have your cake and eat it’ scenario. It is a good option for
cleaning up scattered weeds and to eliminate weed seed-set in all weedy situations
including herbicide resistance. It uses the conventional approach of grain harvest,
plus crop-topping/desiccation at the critical growth stage of the weed.
Timing is critical—it depends on the pulse variety reaching physiological maturity
at or before the time of crop-topping/desiccation. Most pulse varieties (chickpeas,
albus lupin and possibly kaspa field peas) are unsuitable as they are too late and
lose too much grain yield.
4 GenesisTM079 is the earliest of the chickpeas, and only
infrequently does it mature sufficiently to crop top.
11.3 Timing of desiccation
Chickpea are an indeterminate plant with flowering commencing in the lower canopy,
and gradually progressing up the branches (towards the top of the plant) over a
20–30-day period. The problem growers and agronomists are confronted with in
the paddock, is how to maximise yield and quality through the optimal timing of the
desiccant spray. This can be difficult when you have various stages of seed maturity
present on individual plants as well as variability across the paddock.
The optimal stage to desiccate the crop is when the majority (90–95%) of seeds have
reached physiological maturity (seeds are below 35% moisture content). The best
guide at the present time is to base this on a visual inspection of seed\
s by cracking
open pods on each main fruiting branch. Maximum harvest yield is normally reached
when 75% of seeds on each main fruiting branch have turned totally yellow and in
various stages of drying down (turning yellow to brown).
Desiccation should occur when:
• Pods in the top 25% of the canopy are mainly in the final stages of grainfill,
i.e. where the yellow colouring is moving from the ‘beak’ down through the
seed (Photo 1).
• The bottom 75% of pods have all reached, or dried down below, this stage of
maturity. (Seeds have turned totally yellow, and the pod has been bleached to a
very light green-yellow colour) (Photo 1).
4 E Armstrong (2015) Weigh up the risks, benefits of pulse harvest. GRDC Ground Cover Issue 115, Profitable pu\
lses and pastures 02
March 2015, https://grdc.com.au/Media-Centre/Ground-Cover-Supplements/Ground-Cover-I...\
itable-pulses-and-pastures/
Weigh-up-the-risks-benefits-of-pulse-harvest
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Photo 1: Chickpea seeds mature progressively from the bottom to the top
of the plant.
Source: Pulse Australia
Monitoring for desiccation timing
Careful monitoring is needed to determine the correct timing for desiccation in
both chickpea species. Yield reductions of 10–20% can occur if applied too early.
Quality can also be adversely affected. The optimal stage to desiccate chickpea is
when the vast majority of seeds have reached physiological maturity i.e. 90–95%
of the crop. Inspect the seeds within the upper 20% of pods on each main fruiting
branch (Photo 2).
Photo 2:
Correct desiccation timing based on inspection of uppermost pods of
each fruiting branch.
Photo: G Cumming, Pulse Australia
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Seeds are considered to be physiologically mature when the green seed colour
begins to lighten. The Western Australian recommendation of physiological maturity is
‘when the pod wall begins to yellow’ (Photo 3, right).
Photo 3:
LEFT: Pods in the top 25% of the canopy should mainly be in the final
stages of grainfill, where the yellow colouring is moving from the ‘b\
eak’ down
through the seed. RIGHT: The bottom 75% of pods should have reach maturity.
Seeds have turned yellow and the pod has been bleached to a very light
green-yellow.
Photos: G Cumming, Pulse Australia
To avoid the need to inspect seeds, desiccate when 80–85% of pods within the crop
have turned yellow-brown (Photo 4). This is usually too late for the control of ryegrass
survivors.
5
Photo 4: Full maturity, known as ‘rattle pod’, where the seed has detached from the
pod wall and will rattle when shaken.
Photo: G Cumming, Pulse Australia
Seed and pod development
Chickpea plants are indeterminate and the period of flowering can extend from
20–50 days depending on levels of flower abortion and the impact of moisture
stress on the plant. Causes of flower abortion and poor pod-set have been discussed
previously and they include:
• low mean daily temperature (below 15°C)
• frost
• Botrytis grey mould
• extended periods of overcast weather.
Flowering commences on the main stem and basal branches, and proceeds upward
at intervals of ~2 days between successive nodes on each fruiting branch.
Under favourable conditions, the time taken from flowering to the visual appearance
of the pod (pod-set) is ~6 days. After pod-set, the pod wall grows rapidly for the next
10–15 days to assume full pod size. The seeds start to develop at about the same
time as the growth of the pod wall ceases.
5 Pulse Australia (2015) Desiccation and crop-topping in pulses. Pulse Australia, Australian Pulse Bulletin, http://www.pulseaus.com.au/
growing-pulses/publications/desiccation-and-croptopping
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Seed growth occurs over the next 20 days. Pod and seed maturation is also very
staggered along each fruiting branch, although it is generally more compressed and
of shorter duration than flowering owing to the effects of higher temperatures and
varying degrees of moisture stress on the plant. The problem faced by agronomists
in a commercial paddock situation is how to optimise the timing of the desiccant
spray when there are various stages of seed maturity present on individual plants,
as well as variation across the paddock. This can be compounded by variation in soil
type or paddock micro-relief adding to the problem of uneven crop maturity. Some
agronomists use a rule of thumb that when 90% of the field is 90% mature they will
advise growers to spray it out. Alternatively, when larger areas are involved, they
may split soil types and test them separately for desiccation timing. Often, inspection
of commercial crops nearing desiccation reveals that while the lower 30% of pods
have dried to below 15% seed moisture (seeds detached from pod and rattle when
shaken), the upper 30% of pods on each fruiting branch are still at 30–40% moisture
content and in varying stages approaching physiological maturity.
6
Effect of desiccants on immature seeds
Desiccants should not be applied too early as they can affect green seeds. The result
can be a reduction in grain size and yield, an increase in immature seeds, an increase
in greenish discolouration of the seed coat and a reduction in seed viability (Table 1).
Glyphosate does impact on the normal seedling count in germination tests.. Do not
use it in crops destined for sowing seed.
Table 1: Effects of desiccation timing on seed viability.
Trial and
treatment Crop stage
% normal
seed % abnormal
seed % dead seed
None Mature pods8794
Roundup® Mature pods84142
Ally® &
Roundup® Mature pods
85132
Ally® &
Roundup® Mature pods
76204
Ally® &
Roundup® 70% green
pods 15
6322
Ally® &
Roundup® All green pods
226018
Source: Qld DPI (1999)
11.3.1 Products for the desiccation of chickpea
1. Reglone® is registered at 2–3 L/ha
2. Reglone® provides quick leaf drydown but the chickpea plant and weeds can
quickly regrow if moisture is available
3. Roundup PowerMAX® is the only glyphosate registered for chickpea desiccation
4. a) For chickpea desiccation: Roundup PowerMAX® at 0.68–1.8 L/ha
5. b) For additional weed and chickpea desiccation: Roundup MAX® at 0.5–1.1 L/ha
plus Ally® at 5 g/ha
6. Roundup PowerMAX® and Roundup PowerMAX®/Ally® will kill the plants
reducing the likelihood of regrowth
7
Table 2: Chemicals registered for desiccation in chickpeas.
6 Pulse Australia (2013) Northern chickpea best management practices training c\
ourse manual—2013. Pulse Australia Limited.
7 B O’Mara, S Belfield, G Cumming (2007) Chickpea harvest and seed stora\
ge. Pulse Australia, www.pulseaus.com.au/storage/app/
media/crops/2007_Chickpea-Harvest-Storage.pdf
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Herbicide example
trade names operation
Rate Withholding
period
Diquat
200g/L Reglone®
Desiccation2 to 3 L/ha Grazing/stockfeed
(GSF): 1 day
Harvest: 0 days
(lupin, dry pea)
2 days (chickpea,
lentil, faba bean)
Paraquat
250g/L Gramoxone®
Croptopping400 to 800 mL/
ha GSF: 1 day (7 days
for horses) Stock
must be removed
from treated areas
3 days before
slaughter
Harvest: 7 days
Glyphosate
480g/L Ripper 480®
Desiccation765 mL to
2.025 L/ha GSF: 7 days
Harvest: 7 days
Glyphosate
540g/L Roundup
PowerMAX® Desiccation
680 mL/ha to
1.8 L/ha GSF: 7 days
Harvest: 7 days
Metsulfuron
+ Glyphosate
540 g/L Ally® +
Roundup
PowerMAX® Desiccation
+ knockdown
weed control 5 g + 500 mL to
1.1 L/ha GSF: 7 days
Harvest: 7 days
Saflufenacil Sharpen® Desiccation34 g/ha plus
recommended
label rate of
glyphosate
or paraquat
herbicide plus
1 % Hasten or
high quality
MSO GSF: 7 days
Harvest: 7 days
GSF - Withholding period for grazing or cutting for stock food
Note: Observe the Harvest Withholding Period and GSF for each crop.
Source: Pulse Australia
Paraquat is registered for crop-topping; however, may not be effective on grass seed-
set as chickpeas mature quite late relative to grasses.
The major differences between timing of desiccation and crop-topping are\
:
• application timing is different and initiated by different criteria
• herbicides for crop-topping and desiccation are not always the same
• herbicide rates for desiccation are higher than that required for crop-topping
• crop-topping will advance the harvest timing in some pulse crops
• neither desiccation nor crop-topping can be used effectively in all pulses
• both will cause reduced grain quality and yield if applied at the wrong maturity
stage of the crop.
8
NOTE: Desiccation can affect seed viability if applied incorrectly. To avoid damaging
seed viability, it is advisable not to desiccate or crop-top a pulse seed crop.
11.4 Crop-topping
Crop-topping is timed to prevent weed seed-set, not by the crop growth stage.
Hence, crop-topping is generally not possible in chickpea, as they are too late in
maturing. Crop-topping chickpeas can result in discoloured cotyledons (kernel) and
seed coats, leading to rejection at delivery and/or severe downgrading. Even in other
8 Pulse Australia (2015) Desiccation and crop-topping in pulses. Pulse Australia, Australian Pulse Bulletin, http://www.pulseaus.com.au/
growing-pulses/publications/desiccation-and-croptopping
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pulses, growers need to be aware of grain quality defects if crop-topping is done
earlier than the crop desiccation or windrowing stage.
Genesis™ 079 is the earliest maturing chickpea variety, but in most cases, it will not
mature early enough to enable efficient crop-topping without grain quality impacts.
Evidence of the lack of suitability of crop-topping in chickpea is provi\
ded in Table
3, from a South Australian Research and Development Institute crop-topping trial
at Melton, South Australia, in 2009. Visual grain quality data are not presented, but
in this trial:
• Many responses to crop-topping treatments may have been masked by rapid
senescence from a rapid, early seasonal finish (e.g. Almaz
P and Genesis™ 114).
• When crop-topped at the recommended stage, yields were 69–86% of the
untreated control (31–14% yield loss). When crop-topped 2 weeks after the
optimum stage for ryegrass, yields were 92–114% of the untreated control. When
crop-topping was 3 weeks ahead of the recommended ryegrass stage, yields
were 17–48% of the untreated control (83–52% yield loss).
Table 3: Impact of crop-topping timing on chickpea varieties of differing maturity
compared with an untreated control at Melton, South Australia, 2009 Pink shading
denotes significant difference from the control treatment.
Control yield
(t/ha) Yield (% of control) for each timing
Control grain
weight
(g/100 seeds) Grain weight (% of control) for each
timing
Minus 3 weeks
(9 Oct.) Recommended
ryegrass
control stage (30 Oct.) Plus 2
weeks
(12 Nov.) Minus 3
weeks
(9 Oct.) Recommended
ryegrass control stage
(30 Oct.) Plus 2
weeks
(12 Nov.)
Almaz
P 1.18 19 83 9227.4 9192 91
PBA Slasher
P 1.96 30 70 9915.5 87 84 100
PBA HatTrick
P 1.37 36 69 85 18.177 81 93
Genesis
TM 079 2.09 25 80 107 18.0 95104 104
Genesis
TM 090 1.43 25 84 9722.1 79 93 93
Genesis
TM 114 0.90 17 86 11422.1 96102 104
Genesis
TM 509 1.96 32 71 96 13.6 129 101 94
Howzat
P 1.70 21 72 9416.6 87 87 117
Sonali 2.1340 77 104 14.5 96 80 101
Mean (t/ha) 1.900.6 1.51.90 18.616.3 15.9 18.2
Mean (g/100) 18.616.3 15.9 18.2
Source: M Lines and L McMurray (SARDI), Southern Pulse Agronomy Research trials
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