Best Management Practice
Manual 2014
For Agronomists and Growers
Wheat
Canola
Barley
Maize
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Introduction
Clearfield® and Clearfield® Plus crops are extremely useful tools for Australian growers to optimise
production in wheat, barley, canola and maize. Herbicide-tolerant Clearfield and Clearfield Plus
crops simplify control of hard-to-kill weeds with high
yielding non-GMO varieties.
The Clearfield and Clearfield Plus Production Systems combine:
• High yielding, herbicide-tolerant varieties from Australia's leading plant breeders and seed
companies. These varieties are not GMO's and are tolerant to Clearfield herbicides.
• Custom-designed Clearfield herbicides for knockdown and residual weed control
• Clearfield Sustainability Program.
Crops with Clearfield traits are now available in a number of forms:
1. Clearfield wheat varieties: tolerant to and registered for OnDuty® Herbicide only.
2. Clearfield Plus wheat varieties: tolerant to and registered for Intervix® Herbicide.
3. Clearfield Scope barley tolerant to and registered for Intervix Herbicide.
4. Clearfield canola varieties: tolerant to and registered for OnDuty Herbicide and Intervix Herbicide.
5. Clearfield maize varieties: tolerant to and registered for Lightning® Herbicide.
These registrations enable growers to control over 40 weed species including annual ryegrass, brome
grass, barley grass, volunteer cereals, climbing buckwheat and wild oats, using either:

OnDuty on Clearfield wheat, or

Intervix on Clearfield Plus wheat varieties or Clearfield Scope Barley.

Intervix or OnDuty on Clearfield canola.

Lightning on Clearfield maize.
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Clearfield Stewardship Summary
Clearfield crops were introduced into Australia in 1999, with Clearfield canola the first crop. Since
then, Clearfield Wheat, Clearfield Maize, Clearfield Plus Wheat and Clearfield Barley have been
added to the portfolio of crops.
With the growing of the Clearfield Production System crops, comes the responsibility of all parties
(BASF, seed breeders, Clearfield Agencies, Clearfield Accredited Agronomists and growers) to
manage the sustainability of the Clearfield Production System. With the recent introduction of other
herbicide tolerant cropping systems (eg Roundup Ready® canola) greater flexibility in solutions has
become available but with multiple systems comes an increasing complexity, making the Clearfield
Best Management Practices document as important as ever.
This document outlines the Best Management Practices that will result in sustaining the Clearfield
Production System as a key tool for all.
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Contents
1.0 Clearfield and Clearfield Plus Wheat ......................................................................................... 1
1.1 Clearfield Canola .................................................................................................................... 1
1.2 Clearfield Herbicides .............................................................................................................. 2
2.0 Herbicide resistance management in Clearfield Crops ............................................................. 3
2.1 Herbicide resistance management using an Integrated Weed Management (IWM)
approach....................................................................................................................................... 3
2.2 Weed and weed seed management for resistance management ......................................... 3
2.3 Development of resistance..................................................................................................... 3
2.4 Integrated weed management strategies for Clearfield & Clearfield Plus Crops. ................. 6
2.5 General Recommendations for Group B Herbicides ............................................................ 7
3.0 Optimised Weed Control with Clearfield Herbicides.................................................................. 8
3.1 OnDuty Herbicide for Clearfield wheat varieties. ................................................................... 8
3.2 Intervix Herbicide for Clearfield Barley, Clearfield Canola and Clearfield Plus Wheat. ........ 9
4.0 Controlling Volunteers from Clearfield Crops .......................................................................... 11
4.1 Summary .............................................................................................................................. 11
4.2 Important reasons to control volunteers............................................................................... 11
4.3 Controlling volunteers........................................................................................................... 12
4.4 Management actions ............................................................................................................ 12
5.0 Managing Out-crossing ............................................................................................................ 13
5.1 What is out-crossing? ........................................................................................................... 13
5.2 Potential for out-crossing in Clearfield and Clearfield Plus wheat ....................................... 13
5.3 Description of Triticum aestivum varieties with Clearfield and Clearfield Plus Technology 13
5.4 Potential for out-crossing to non-Clearfield and Clearfield Plus wheat varieties ................. 14
5.5 Potential for out-crossing to weed species related to wheat ............................................... 14
5.6 Managing out-crossing of Clearfield and Clearfield Plus wheat to related species ............ 15
5.7 Potential for out-crossing in Clearfield Scope Barley .......................................................... 15
5.8 Description of Hordeum vulgare L. (cultivated barley) varieties with Clearfield Technology
.................................................................................................................................................... 15
5.9 Potential for out-crossing to non-Clearfield barley varieties ................................................ 16
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5.10 Weediness status in Australia and Overseas .................................................................... 16
5.11 Potential for out-crossing to weed species related to barley ............................................. 16
5.12 Managing out-crossing of Clearfield Scope barley to related species .............................. 17
5.13 Managing Clearfield Wheat and Clearfield Scope Barley in the crop rotation: ................. 17
5.14 Potential for out-crossing in Clearfield Canola................................................................... 17
5.15 Description of Brassica napus varieties with Clearfield technology .................................. 17
5.16 Potential for out-crossing to non-Clearfield canola varieties ............................................. 18
5.17 Potential for out-crossing to weed species related to Canola ........................................... 18
5.18 Managing out-crossing of Clearfield canola to related species ......................................... 19
5.19 Potential for out-crossing in Clearfield Maize .................................................................... 19
5.20 Managing practices for Clearfield maize ............................................................................ 20
6.0 Contacts ................................................................................................................................... 21
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1.0 Clearfield and Clearfield Plus Wheat
Australian standard wheat varieties are hexaploid, in other words, they are genetically comprised of
three sets of paired chromosomes known as genomes. Clearfield wheat (or one-gene) varieties have
experienced a mutation in one of their three genomes enabling that genome to produce ALS enzyme
that is unaffected by imidazolinone herbicides. The other two genomes lack the mutation and produce
sensitive ALS enzyme. One-gene wheat varieties are therefore in effect one-third tolerant of
imidazolinone herbicides (and two-thirds sensitive).
Clearfield Plus (or 2-gene) wheat varieties have a separate mutation on a second genome so that
two of their three genomes enabling those genomes to produce ALS enzyme that is unaffected by
imidazolinone herbicides. The other single genome lacks a mutation and produces sensitive ALS
enzyme. Two-gene wheat varieties are therefore in effect two-thirds tolerant of imidazolinone
herbicides (and one-third sensitive).
Neither Clearfield nor Clearfield Plus wheat varieties are therefore completely resistant from
imidazolinone injury but Clearfield Plus wheat lines are considerably more tolerant. This is
demonstrated by the fact that CL JNZ and CL STL (the only two released varieties of Clearfield
wheat) do not have adequate tolerance to Intervix Herbicide. By contrast the new Clearfield Plus
wheat lines are able to tolerate Intervix. Note: Intervix herbicide cannot be used on non-Clearfield
wheat varieties, nor can Intervix be used on non-Clearfield barley varieties, as severe crop damage
will occur.
Development of new Clearfield Plus two gene wheat cultivars is ongoing in partnership with all major
wheat breeding programs in Australia. Single gene Clearfield development has been discontinued.
1.1 Clearfield Canola
Clearfield Canola features some of the highest yielding varieties with the highest oil content available
in Australia. These varieties are tolerant to Intervix herbicide. Intervix controls almost 30 weeds
including wild radish, mustard, turnip and a range of grass weeds. Note: Intervix cannot be used on
non- Clearfield canola varieties as sever crop damage will occur.
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1.2 Clearfield Herbicides
All Clearfield herbicides are based on the imidazolinone group of herbicides, which are part of the
Group B mode of action. Group B herbicides work by inhibiting acetolactase synthase (ALS enzyme),
an enzyme critical for the production of the essential amino acids leucine, isoleucine and valine which
are used for protein production in plants.
Advice on all Clearfield crops is available from AgriCentre®. AgriCentre staff receive ongoing
training in Clearfield crops and AgriCentre agronomists have completed a detailed Clearfield
accreditation course. An important component of the Clearfield Production System is the stewardship
within the Clearfield Sustainability Program, which details Best Management Practices for Clearfield
Crops. This program has some obligatory practices that are aimed at ensuring the sustainability of
herbicide-tolerant Clearfield crops.
There are four (4) key areas addressed to help ensure the sustainability of Clearfield crops:

Herbicide resistance management using an integrated approach;

Optimising weed control using only Clearfield herbicides for maximising crop yield and
ensuring

Effective weed resistance management;

Control of crop volunteer plants; and

Managing out-crossing to non-Clearfield crops and related weeds
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2.0 Herbicide resistance management in Clearfield Crops
2.1 Herbicide resistance management using an Integrated Weed Management (IWM)
approach
The objectives of herbicide resistance management are to achieve weed control whilst preserving the
value of each herbicide and each herbicide group for the longer term.
Herbicide resistance management programs must consider utilising all available tools to prevent or
delay the onset of herbicide resistance.
2.2 Weed and weed seed management for resistance management
In practical terms, the key to an integrated approach is to reduce the weed seed bank within each
paddock via the use of all available control practices. The use of herbicides is just one of these
practices. Reducing the weed burden within a paddock over time can result in the reduction of
selection pressure on a weed population.
2.3 Development of resistance
Herbicides impose selection pressure for resistance at any rate. Label herbicide rates are a reflection
of efficacy trials that indicate best control and crop yield responses. There are several factors which
determine how quickly resistance develops:
Seedbank Life: Weed seeds with a long seedbank life (seeds which survive for many years in the
paddock) act as a buffer to slow down the onset of herbicide resistance. If resistance starts
developing, a significant proportion of susceptible seeds remain which dilute the resistance pool.
Conversely, resistance can be selected rapidly in weeds with a short seedbank life (common in most
small seeded species such as mustards) because resistant individuals surviving a herbicide dominate
the seedbank whilst susceptible seeds present from previous seasons are more rapidly depleted.
Thus, within a few seasons, resistant individuals can constitute an entire paddock population.
Initial Frequency: The initial frequency of naturally occurring resistant biotypes in a weed population
influences a weed population's potential to develop resistance. Also, the relative fitness or vigour of
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resistant weed biotypes affects resistance development. Generally speaking, the greater the initial
frequency of resistance and the greater the fitness of the resistance biotype, the greater the potential
for resistance to develop in a species population.
Time: The time required for a weed population to develop resistance will vary. Resistance to a
herbicide may occur in as little as two to five years, or it may never develop. For example, resistance
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to triasulfuron developed after being used in two consecutive years of continuous cereals . Triazineresistant weeds occurred after 10 years of continuous use of triazines. The first glyphosate-resistant
field population of ryegrass was found after 15 years of multiple use of glyphosate. The time required
for resistance to develop depends on many factors including:

Selection pressure exerted by the herbicide;

Herbicide and crop rotation patterns;

Seed germination dynamics;

Use of herbicide combinations with different modes of action;

Initial frequency of naturally occurring, resistant individuals in the weed population; and

The relative vigour of resistant biotypes of weeds.
Based on these factors, models have been developed to predict the development of resistance in a
weed population. However, due to the many factors involved and the limited information available on
weed and seed biology, it is impossible to predict exactly when, if ever, a resistant population will
develop. Current models provide an indication of the development of resistance; these indications are
an essential input to the development of resistance management strategies and practices.
The most important factors influencing a plant's potential to develop resistance are:
•
History of herbicide use: continuous use of the same mode of action herbicide in
consecutive years without use of another mode of action herbicide used at the full label
rate to target the same target weeds species may increase the potential for resistance to
develop.
•
Cultural practices: weed control that relies solely on herbicide use and does not
combine tillage or other cultural practices with herbicide applications may increase the
potential for resistant populations
•
to develop.
•
Environmental conditions: environmental conditions that are not conducive to herbicide
breakdown in the soil may increase the potential for resistant populations to develop.
Continuous
dry weather
can slow
the breakdown of
many herbicides
(e.g.
imidazolinones). High soil pH inhibits the breakdown of some herbicides like SU's. The
longer a herbicide persists, the longer it exerts selection pressure on a weed population,
particularly if there are multiple weed flushes in one growing season.
1
P. Boutsalis, The University of Adelaide.
4
•
Composition of the weed population: weed species that are very sensitive to a
herbicide, are prolific seed producers and have large genetic variation are at greater risk
of developing resistance.
•
Weed seed bank: a high soil seed bank within an individual paddock increases the
selection pressure which, in turn, increases the likelihood of resistance developing.
A variety of factors may cause weed control failures. Herbicide resistance is the easiest factor to test
for using a herbicide resistance test. If a weed sample is not resistant on or more other factors are
responsible, such as misapplication, not adhering to herbicide label recommendations, stressed
weeds ad poor environmental conditions.
As with most problems, prevention is the best strategy. Development of herbicide-resistant weeds can
be avoided or delayed through the adoption of good management practices. The recommendations
listed below take into consideration many of the points discussed so far, and are designed to prevent
or delay the onset of weed resistance:
•
Scout fields regularly and understand the biology of the weeds present.
•
Consider the source of crop seeds and their potential to introduce new weed species and
biotypes.
•
Always read and follow herbicide label recommendations.
•
Use crop rotations, notably rotations from dicotyledonous crops to grass crops. Weed
control
•
Options in these types of rotations offer the most diverse means to minimise risk of
resistance development.
•
Use the minimum number of applications of any one herbicide or herbicide group
recommended per season.
•
Use and follow industry recommendations for various competitive weed thresholds.
•
Combine timely cultivation with herbicide treatments as part of the paddock management
strategy, if practical.
•
Use tank mixes or sequential applications of herbicides that have different modes of
action but operate on the same weeds species. The manufacturers of herbicides and the
regulatory authorities have grouped herbicides with similar modes of action. These
modes of action are exhibited on the herbicide labels. The industry publishes strategies
resulting in an effective rotation between these groups.
Managing herbicide resistance is an ongoing battle. Cooperation between the scientific community,
agricultural chemical companies, consultants and government extension personnel is essential to
prevent or delay the onset of herbicide resistance using cost effective strategies. One such strategy
is the use of herbicide tolerant cropping systems.
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2.4 Integrated weed management strategies for Clearfield & Clearfield Plus Crops.
Clearfield crops are tolerant to herbicides based on the imidazolinone group, which are grouped
within the Group B herbicides.
Continuous use of Group B herbicides may result in the selection of weed biotypes resistant to this
group of herbicides. Testing of annual ryegrass for GRDC sponsored random weed surveys across
SA and Victoria have shown that the imidazolinone herbicides control some ryegrass populations that
are resistant to the sulfonylurea herbicides. This is also true for some broadleaf weed biotypes
resistant to sulfonylurea herbicides. Additionally, Intervix Herbicide has shown control of all randomly
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collected samples of Brome grass that were resistant to sulfonylurea and sulfonamide herbicides .
Preservation of the effectiveness of this group of herbicides is vital for efficient and cost-effective
agricultural production in Australia. Therefore, effective management of the potential for the
development of resistant weeds is an important part of overall crop and farm management.
A number of specific management strategies, as outlined below, should be followed when using the
Clearfield Production System. Growers and agronomists should give consideration to each of the
following points, in order to determine an integrated weed management plan and how this fits with
their crop rotation.
•
Always refer to the Clearfield Production System Best Management Practice - Agronomists
and Growers Guide.
•
Always follow product label directions. Application timing is essential for optimum weed
control and hence managing resistance via minimising weed seed production.
•
Apply no more than two (2) Group B herbicides in any four (4) year period on the same
paddock-this strategy will slow the development of resistance. Consideration should be given
to less frequent use to delay the onset of resistance development. This includes the use of
Group B herbicides both within the Clearfield Production System and in conventional crops.
•
Where it is possible, care should be taken to avoid applications of Group B herbicides in
consecutive years unless at least two years' previous good weed control has been achieved
with methods other than Group B herbicides. Years where no Group B herbicide is used will
slow the development of resistance.
•
Use of Group B herbicides in either summer crops or fallow is equivalent to a pre-emergent
application and further Group B applications should not be made.
•
Farming practices, herbicide and crop rotations should be developed, which allow for the use
of alternative mode of action herbicides or methods of weed control.
•
When using crops with Clearfield and Clearfield Plus technology, consideration should be
given to the use of pre-emergence herbicides such as a Group D herbicide (e.g.
pendimethalin or trifluralin), Group C (e.g.metribuzin), Group K herbicides (Sakura® or
2
Peter Boutsalis, The University of Adelaide.
6
Boxer® Gold) or Group J (triallate). Consultation with an accredited agronomist regarding this
use should be undertaken, particularly in situations where moderate to heavy ryegrass
populations exist or where Group B resistance is suspected.
•
Where Group B resistance is suspected within a weed population, testing of the relevant
weeds should be carried out prior to the use of crops in the Clearfield or Clearfield Plus
Production System. Visit www.plantscienceconsulting.com.au for more information.
•
Integrated Weed Management should be undertaken on a paddock-by-paddock basis.
Specific paddock planning should take into consideration the history of the paddock as well as
the future use options.
•
Resistance management guidelines for other herbicide mode-of-action groups should also be
taken into account when developing and planning rotations.
2.5 General Recommendations for Group B Herbicides
1. Not more than one application of a Group B herbicide per season.
2. If a Group B herbicide has been applied as a pre-emergent application DO NOT apply further
Group B herbicides to that crop. Ensure any further post emergent herbicides from another
mode of action group.
3. Apply no more than two (2) Group B herbicides in any four (4) year period on the same
paddock.
4. If a post-emergent Group B herbicide is required, it should be tank mixed with another mode
of action herbicide at the label rate which controls the same target weed outright. If any
further applications are required in that season, it should be with a non-ALS mode of action
herbicide that controls the target weed.
5. A Group B herbicide may be used alone on flowering wild radish only if a Group B herbicide
has not been previously used on that crop.
6. Where a Clearfield herbicide is to be used, refer to the relevant section of this manual.
7. If a post-emergent Group B herbicide is to be used, consider using a non-Group B preemergence herbicide targeting the same species to lower the selection pressure on the Group
B herbicide.
8. Keep accurate records of all herbicide usage.
The above recommendations should be incorporated into an Integrated Weed Management (IWM)
program. In all cases, ensure surviving weeds from any treatment do not set and shed seed. Adopt
the integrated strategies mentioned in this document, including the rotation of mode of action groups.
Make sure you rotate between products from different mode of action groups. Utlise strategies such
as crop-topping, windrow burning, chaff carts and The Harrington Seed Destructor.
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3.0 Optimised Weed Control with Clearfield Herbicides
3.1 OnDuty Herbicide for Clearfield wheat varieties.
NOTE: CL JNZ and CL STL have adequate but limited tolerance of OnDuty Herbicide. These crops
do not tolerate Intervix Herbicide.
Objective: achieve optimum weed control and maintain weed resistance management practices.
1. Monitor the crop for crop growth, insect attack and weed growth regularly after sowing.
Ensure the crop is free of all avoidable stress at the time of application.
2. Apply under appropriate environmental conditions when the crop has reached at least the 4
leaf stage. If the crop shows staggered growth, delay applications until 80% of plants have
reached the 4 leaf stage.
3. Use caution to avoid the potential for drift to susceptible crops. Adopt good application
practices that minimise spray drift.
4. Decontaminate the boom sprayer and associated equipment before spraying the crop with
OnDuty Herbicide.
5. Watch out for residues of sulfonyl urea herbicides.
6. Fit the appropriate nozzles for the recommended water volume of no less than 70L/ha
(medium/coarse to coarse droplet recommended).
7. Recalibrate the sprayer for the higher water volumes recommended for OnDuty.
8. Decontaminate the boom sprayer and associated equipment after applying OnDuty
Herbicide.
9. Monitor weed growth:
•
Weeds will stop growing and competing with the crop almost immediately after
OnDuty is taken up. Complete death of weeds may take from 4-6 weeks after
spraying.
•
During this time, weeds do not compete with the crop. Weeds change colour
progressively from green to either yellow or purple/red.
•
OnDuty may have a short-term, transient check on crop growth while plants detoxify
the herbicide within their tissues. Under adverse growing conditions this check can be
more pronounced and the crop may also show some transient yellowing.
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•
OnDuty may not control Group B resistant grass plants and Group B resistant
broadleaf plants.
3.2 Intervix Herbicide for Clearfield Barley, Clearfield Canola and Clearfield Plus
Wheat.
Objective: achieve optimum weed control for crop yield, and enhance weed resistance management.
1. Monitor the crop for crop growth, insect attack and weed growth regularly after sowing.
Ensure the crop is free of all avoidable stress at the time of application.
2. Timing: The ALS enzyme is more concentrated in young, rapidly growing plant material.
Spray as soon as conditions allow application when the crop has reached the following
growth stages:
•
Clearfield Barley– 3-leaf stage to 1st node stage (Z31). Application earlier than the 3leaf stage may cause unacceptable crop injury under stressful conditions.
•
Clearfield Canola – 2-leaf stage and no later than the 6-leaf stage. Applications
earlier or later than this window are safe to the crop but may impact weed control.
•
Clearfield Plus Wheat – 3-leaf stage to 1st node stage (Z31). Application earlier than
the 3-leaf stage may cause unacceptable crop injury under stressful conditions.
Intervix Herbicide has knockdown and residual activity on weeds. It's best not to delay spraying while
waiting for a “complete” germination of weeds. Best results and crop yield are obtained by spraying
actively growing crops and weeds as soon as possible after the growth stages presented above for
each crop type. It has been documented that plants with weak resistance can be controlled if young
and actively growing and that control is reduced as plants get older.
1. Use caution to avoid the potential for drift to susceptible crops. Adopt good application
practices that minimise spray drift.
2. Application:
•
For Clearfield Barley apply Intervix Herbicide at the recommended rate of
375 – 750ml/ha in no less than 70L of water/ha with Hasten® at 1.0% v/v or
Supercharge® at 0.5% v/v. Where appropriate, add tank mix partner
herbicide according to Intervix label instructions.
•
For Clearfield Canola apply Intervix Herbicide at the recommended rate of
300 - 500mL/ha or 600 - 750mL/ha in a no less than 70L of water/ha with
Hasten® at 1.0% v/v or Supercharge® at 0.5% v/v. Where appropriate, add
tank mix partner herbicide according to Intervix label instructions.
•
For Clearfield Plus Wheat apply Intervix Herbicide at the recommended
rate of 375 – 750ml/ha in no less than 70L of water/ha with Hasten® at 1.0%
9
v/v or Supercharge® at 0.5% v/v. Where appropriate, add tank mix partner
herbicide according to Intervix label instructions.
3. Decontaminate the boomsprayer and associated equipment before spraying the crop with
Intervix Herbicide. Watch out for residues of sulfonylurea herbicides.
4. Fit the appropriate nozzles for the recommended water volume of no less than 70L/ha.
5. Recalibrate the sprayer for the higher water volumes recommended for Intervix.
6. Decontaminate the boom sprayer and associated equipment after applying Intervix
Herbicide.
7. Do not apply Intervix if rainfall is expected within the following two (2) hours. Ensure label
instructions for rainfastness of tank mix herbicide partner are followed if a registered tank mix
used.
8. Monitor weed growth:
•
Weeds will stop growing and competing with the crop almost immediately after
Intervix is taken up. Complete death of weeds may take from 4-6 weeks after
spraying.
•
During this time, weeds do not compete with the crop. Weeds change colour
progressively from green to yellow or purple/red.
9.
Under adverse growing conditions crop growth may be suppressed and some transient
yellowing may be seen as crops detoxify the herbicide within their tissues, especially if crops
are treated around the 3-leaf stage.
10. Intervix will suppress some species to the extent that they may present little or no
competition to the crop. The developing crop canopy will provide further limitation to their
growth and competitive status. The use of Lontrel will significantly improve control on species
such as capeweed and thistles.
11. Intervix is a broad-spectrum herbicide with contact knockdown activity on weeds and nontolerant crops alike. Exercise caution when applying Intervix Herbicide, and maintain good
spray application techniques. In particular, avoid spray drift of Intervix Herbicide onto
neighbouring crops and pastures of all kinds (medium/coarse to coarse droplet
recommended).
12. Where ryegrass populations are moderate to high or if Group B resistant ryegrass is present
or suspected to be present it is recommended to use a pre-emergence herbicide from an
alternative Group eg Group D, J or K as appropriate.
13. Always refer to the latest labels of OnDuty and Intervix herbicides for specific directions for
use before application.
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4.0 Controlling Volunteers from Clearfield Crops
Objective: control of all volunteers from Clearfield crops before flowering.
4.1 Summary
•
Best Management Practice is to control volunteer plants in the year following when a
Clearfield or Clearfield Plus Production System crop has been grown.
•
DO NOT rely on Group B herbicides to control volunteers.
•
Volunteers from Clearfield and Clearfield Plus crops will be controlled by all herbicides
currently
•
registered for control of conventional crops, except for Group B herbicides. For example
volunteer Clearfield canola will be controlled by herbicides from Group C (eg atrazine),
Group I (eg MCPA, 2,4-D), Group F (eg Paragon® Xtra), Group H (eg Velocity®), Group
G (eg Sharpen®) and knockdown herbicides such as glyphosate and paraquat.
•
Clearfield Plus Wheat and Clearfield Barley volunteers will be controlled by glyphosate,
paraquat, Group A herbicides (eg clethodim) and simazine. NOTE: Clearfield and
Clearfield Plus wheat plants, and Clearfield barley plants, cannot be controlled in-crop
in conventional cereals, they must be controlled pre-sowing. Clearfield canola plants
cannot be controlled in-crop in conventional canola- they must be controlled pre-sowing.
Atrazine and Roundup Ready Herbicide will provide in-crop control in TT and RR crops
respectively.
•
Clean-up and farm hygiene during all stages of sowing, harvesting, storage and transport
are important in the effective control of volunteers.
•
To facilitate volunteer control monitor paddocks during the growing year and the year
after growing Clearfield and Clearfield Plus crops.
•
Best Management Practice is to make volunteer control part of weed, pest and disease
management strategies for the farm.
4.2 Important reasons to control volunteers
•
Volunteer plants act as competitive weeds in following crops or pastures.
•
Volunteer plants may result in contamination of grain.
•
Volunteers may be important in the build-up and spread of major diseases.
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•
Volunteers increase the risk of herbicide tolerance spreading from cross-pollination of
volunteer plants and neighbouring paddocks containing the same crop species.
4.3 Controlling volunteers
A combination of hygiene, cultural and herbicide options are available to control volunteers including:
•
Minimise seed losses through close attention to timeliness of harvesting.
•
Correct setup of harvest equipment.
•
Seal all holes and cracks in harvest equipment which allow spillage, even of small
quantities of seed (especially in the table, front elevator and grain tank).
•
To avoid the inadvertent spread of Clearfield and Clearfield Plus varieties between
paddocks, along farm tracks, public roads and roadsides at harvest, thoroughly clean out
harvest equipment using high pressure air blowers/suckers.
•
Practice good hygiene at harvest and during transport of grain to on-farm storages;
practice good stubble management after harvest.
•
Spray any seed that germinates with summer rains with a knockdown herbicide at robust
rates.
•
Control ALL volunteers in following crops or pastures with pre-sowing knockdown or with
in-crop herbicides.
4.4 Management actions
•
Record and clean up all accidental seed spillage on and off the farm-check later for
germination of volunteers and control with robust rates of knockdown herbicides.
•
Keep good field records of herbicides used in previous crops and herbicide-tolerant
varieties in neighbouring paddocks to develop effective plans for controlling volunteers.
•
A crop of the same species should not follow a Clearfield or Clearfield Plus crop, as
controlling volunteers within the same crop species is difficult. If successive wheat or
barley crops are grown, seed should not be saved from the second crop due to the fact
that volunteer seed from the previous crop may be present.
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5.0 Managing Out-crossing
5.1 What is out-crossing?
Out-crossing (or cross-pollination) can be defined as the ability of a plant species or variety to
pollinate a plant of a different, related species or variety. A wide range of factors influence the ability
of a given plant to out-cross with others, such as timing of flowering, pollen dispersal, pollen viability
and environmental conditions. The likelihood of out-crossing varies greatly from species to species
and variety to variety. Successful out-crossing may result in the offspring displaying characteristics of
both parent plants.
The risk of out-crossing can vary significantly between crop and weed species. The focus for
management must therefore be on the control of volunteers and managing herbicide-tolerant crops
and related species.
Each Clearfield crop is covered individually due to the difference in potential for out-crossing.
5.2 Potential for out-crossing in Clearfield and Clearfield Plus wheat
Specific information is provided here in relation to possible out-crossing of resistant traits to other
wheat varieties and related species.
5.3 Description of Triticum aestivum varieties with Clearfield and Clearfield Plus
Technology
Clearfield wheat varieties (CL JNZ and CL STL) have tolerance to OnDuty Herbicide and Clearfield
Plus wheat varieties have tolerance to Intervix Herbicide. Current Clearfield and Clearfield Plus
varieties were derived from inbreeding and chemically-induced modification. They were not derived
from recombinant DNA technology, i.e. they are not GMOs. These varieties were developed via
conventional back-crossing methods. The majority of wheat varieties grown in Australia are pure
lines, derived from inbreeding. The tolerance has been introduced only into white spring wheat
varieties to date.
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5.4 Potential for out-crossing to non-Clearfield and Clearfield Plus wheat varieties
Although wheat cultivars are classified as self-pollinators, out-crossing in wheat has been
documented in both winter and spring wheat cultivars, albeit at very low incidences. Out-crossing
rates of 0.1 - 5.6% among winter wheat have been reported. Increased out-crossing rate was not
associated with semi-dwarf stature. A range of 0.3 - 6.05% out-crossing among Canadian spring
wheat cultivars has also been reported. Studies show that out-crossing tended to be highest among
cultivars with low pollen staining, spikes that tapered at the extremities and with greater spikelet
opening at anthesis. There have been no reports showing that Triticum aestivum exhibits
characteristics of a pest or that it is a weed in Australia.
Centuries of breeding of wheat varieties has selected for a number of traits resulting in the modern
wheat, which has a poor ability to survive in the wild. Traits such as heads that did not shatter were
favoured due to easier harvest but this trait placed the wheat plants at a disadvantage to plants of
other species, which could more efficiently distribute seed. In addition, hull-less type plants were
easier to thresh but exposed the developing seed to undesirable environmental extremes.
Despite these disadvantages, plants of modern wheat cultivars are occasionally found in uncultivated
fields and roadsides. These occurrences are usually associated with grain dropped during harvest or
transport. Plants growing in these environments do not persist, and are usually eliminated by mowing,
cultivation and/or herbicide application.
Wheat plants may also grow as volunteers in a cultivated field following a wheat crop. Volunteers that
germinate in a crop or fallow following the use of Clearfield or Clearfield Plus crops should be
controlled before flowering, as outlined in the Controlling Volunteers section of this Obligatory
Practice.
After almost 200 years of cultivation in Australia and throughout the world, there have been no reports
of wheat becoming an invasive pest.
In short, out-crossing to other wheat varieties is possible. However, the likelihood of this occurring is
greatly diminished when the Clearfield Best Management Practices are followed (ie good hygiene
and appropriate rotation practices, and control of volunteers prior to flowering). As wheat pollen is
relatively heavy and unlikely to travel greater than 3m, the likelihood of out-crossing is considered
remote.
5.5 Potential for out-crossing to weed species related to wheat
There are only a few reports concerning natural cross hybridisation with related species and genera.
Hybridisation within the genus Triticum has been shown to be generally less than 6%. While
hybridisation between cultivated wheat and related species can occur, no known wild Triticum species
exist in Australia.
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When out-crossing does occur, it is generally due to close contact between flowers of different
varieties (within 3m). A well-known inter-generic combination involving wheat is triticale, derived from
crossing wheat and rye (Secale cereale). There have been no reports of triticale serving as a bridge
for hybridisation with other wild grass species.
Complex hybrids have been made between wheat and several species of Agropyron including A.
curvifolium, A. distichum and A. juceum. There are no known reports of hybridisation between wheat
and the weed species A. repens, and all reports of wheat-Agropyron hybrids involved deliberate
cross-pollinations in greenhouse settings.
There are no known relatives of T. aestivum in Australia. While it is possible to produce hybrids
between wheat and Agropyron species, no known naturally occurring hybrids or derived species have
been reported. Therefore, out-crossing to related weed species is considered highly unlikely.
5.6 Managing out-crossing of Clearfield and Clearfield Plus wheat to related species
As stated, the likelihood of out-crossing to related species is low for wheat. However, the following
practices should be followed to help minimise the potential for out-crosses occurring:
•
Control all volunteers in the season after growing Clearfield or Clearfield Plus Wheat.
•
If consecutive wheat crops are grown (of which one is Clearfield or Clearfield Plus Wheat),
do not save seed from the second crop. Saved seed may contain both varieties, which may
increase the likelihood of outcrossing when next planted.
•
Maintain hygiene along fence-lines where different wheat varieties may germinate.
•
Cover loads during harvest and transport to avoid dispersing seed.
5.7 Potential for out-crossing in Clearfield Scope Barley
Specific information is provided here in relation to possible out-crossing of resistant traits to other
barley varieties and related species.
5.8 Description of Hordeum vulgare L. (cultivated barley) varieties with Clearfield
Technology
The majority of barley varieties grown in Australia are pure lines, derived from inbreeding. Clearfield
Scope Barley is derived from in-breeding and chemically-induced modification. It is not derived from
recombinant DNA technology, i.e. Clearfield Scope Barley is not a GMO. Clearfield Scope barley
has tolerance to Intervix Herbicide.
The tolerance has only been introduced into spring barley
varieties to date.
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5.9 Potential for out-crossing to non-Clearfield barley varieties
Although cultivated barley and its wild progenitor both reproduce almost entirely by selffertilisation/pollination, some isolated cases of out-crossing have been reported, albeit at extremely
low incidences. In experiments designed to measure outcrossing rates in barley plants in physical
contact with each other, the average rate of outcrossing was about 0.8%. The rate of out-crossing fell
to 0.2% when physical contact was virtually eliminated by spacing plants 30cm apart, and when
plants were 60cm or 90cm apart, the pollen migration rate fell to approximately 0.1%. Pollen migrants
were only detected sporadically when pollen donor and recipient plants were separated by 3m, and
no outcrossing was detected when plants were separated by 10m. Barley is not generally pollinated
by insects, so any outcrossing occurs by wind pollination and distance is the most important factor
that influences rates of out-crossing as a result of pollen migration in barley.
In observations of pollen migration between commercial barley fields, outcrossing rates were 0.05%
and 0.01% for distances of 1m and 10m, respectively. No pollen migrants were observed in these
studies at distances of 20m or 50m. However, cross fertilisation with very low frequencies has been
observed at distances of up to 50m and 60m (although cross pollination at such distances is rare).
In short, out-crossing to other barley varieties is possible. However, the likelihood of this occurring is
greatly diminished when the Clearfield Best Management Practices are followed (ie good hygiene
and appropriate rotation practices, and control of volunteers prior to flowering).
5.10 Weediness status in Australia and Overseas
H. vulgare occurs as an escape from cultivation and is present throughout Australia. It is listed as a
naturalized non-native species present in all Australian states and territories with the exception of the
Northern Territory. Barley is considered a minor weed in natural ecosystems, but is primarily a
problem in agricultural or rural environments. Barley is likely to occur anywhere seed is dropped and
often grows on roadsides, but seldom persists. Barley crop derived seed can develop into volunteers,
but only at a very low frequency.
In an environment assessment done by the USDA/APHIS in 1994, it was stated that barley
occasionally escapes and becomes weedy or naturalized. However, barley is not reported as a
serious or principle weed and there are no reports of barley becoming a significant weed in the US.
5.11 Potential for out-crossing to weed species related to barley
The other related species present in Australia include Hordeum glaucum, H. hystrix, H. leporimum, H.
marimum, H. murinium, H. secalimim, secale cereal and Triticum aestivum. Although some of these
are weedy, none can cross with cultivated barley under natural conditions. In relation to interspecific
crossing, with few exceptions the isolation barriers (usually hybrid sterility) are very strict between the
Hordeum species and there is little or no genetic exchange in nature due to lack of chromosome
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pairing, even where two taxa have sympatric distribution, Intergeneric hybrids can be obtained
between barley cultivars and diploid, tetraploid and hexaploid wheats, but only with extensive
intervention such as hormone applications, chemical treatment and embryo rescue.
5.12 Managing out-crossing of Clearfield Scope barley to related species
As stated, the likelihood of out-crossing to related species is extremely low for barley. However, the
following practices should be followed to help minimise the potential for out-crosses occurring:
•
If consecutive barley crops are grown (of which one is Clearfield Scope Barley), do not save
seed
•
from the second crop. Saved seed may contain both varieties, which may increase the
likelihood of outcrossing when next planted.
•
Maintain hygiene along fence-lines where different wheat or barley varieties may germinate.
•
Cover loads during harvest and transport to avoid dispersing seed.
•
Control all volunteers in the season after growing Clearfield Scope Barley.
5.13 Managing Clearfield Wheat and Clearfield Scope Barley in the crop rotation:
•
It is not recommended to follow Clearfield Wheat with Clearfield Scope Barley or vice-versa.
If this practice is carried out it is critical to control all volunteers from the previous and
subsequent Clearfield crops. Seed should not be saved from the 2nd crop.
•
In the event of growing two (2) Clearfield cereal crops in succession, ALWAYS ensure
herbicide resistant management general recommendations for Group B Herbicides are
followed in accordance with the integrated weed management strategies for Clearfield Crops.
Apply no more than two (2) Group B herbicides in any four (4) year period on the same
paddock.
•
In a situation where it is intended to grow barley following a wheat crop, Clearfield Scope
Barley may prove a useful tool in managing volunteer wheat (non-Clearfield varieties) in the
barley crop.
5.14 Potential for out-crossing in Clearfield Canola
Specific information is provided here in relation to possible out-crossing of resistant traits to other
canola varieties and related species.
5.15 Description of Brassica napus varieties with Clearfield technology
Clearfield canola varieties have tolerance Intervix Herbicide and OnDuty Herbicide. Current
Clearfield varieties were derived from inbreeding and chemically induced modification. They were not
derived from recombinant DNA technology. These varieties were developed via conventional backcrossing methods. The majority of canola varieties grown in Australia are pure lines derived from
inbreeding. A range of Clearfield Canola varieties are available with maturities to suit all canola
growing regions.
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5.16 Potential for out-crossing to non-Clearfield canola varieties
Brassica napus (canola) varieties are predominantly self-pollinated, and pollinating agents such as
wind and insects are responsible for only a small proportion of cross-pollination. Cross-pollination
and out-crossing may vary according to variety, proximity and environmental factors, and in proximate
plants may range from 3-20%. There is a chance of intra-specific crosses. Cross-pollination
decreases with increasing distance from pollen source. Pollen movement decreases exponentially
with distance from the source. This is because:
•
Pollen viability is short lived;
•
Honeybee behaviour (i.e. they clean their bodies of pollen before returning to a crop); and
•
Competition between self-fed and foreign pollen in fertile plants.
•
Therefore, the probability of cross-pollination and gene transfer by pollen from Clearfield crops is low.
Contamination of herbicide-resistant canola varieties has been recorded following cross-pollination of
paddocks in close proximity and as a result of physical admixture of seeds during harvesting. Crosspollination and transfer of herbicide-resistant canola plants is neither a new phenomenon nor a major
threat, however advisors and end-users need to be aware of the risks and the consequences. Low
levels of cross-pollination between neighbouring canola fields is to be expected. An assessment of
the risk of out-crossing and hybridization from imidazolinone tolerant Brassica napus must consider
the following factors:
•
The imidazolinone tolerance trait originated by conventional selection of a mutation in a native
gene.
•
As a result, the range of genotypes and phenotypes that may be produced with this trait do
not fall outside the experience of traditional genetics and plant breeding.
•
Transfer of imidazolinone tolerance in recipient plants requires the independent inheritance of
two genes. Gene action is additive and shows incomplete dominance. This does not favour
survival of heterozygous individuals for this herbicide resistance trait.
Given this information, a low potential for out-crossing between Clearfield canola and other varieties
does exist. For this reason, consideration should be given to avoiding the planting of Clearfield
canola adjacent to other non-Clearfield canola varieties. In addition, Best Management Practice is to
ensure other canola crops do not proceed or follow Clearfield canola crops. Control of volunteers in
all situations is important in assisting to prevent out-crossing.
5.17 Potential for out-crossing to weed species related to Canola
In all the research literature reviewed by Scheffler and Dale (1994), the possibility of hybridisation
between Brassica napus and related species, even under optimum conditions, is often low. Methods
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of ovule culture and embryo rescue, developed over several decades, have extended the range of
species that can be sexually hybridised with Brassica napus. However, such in vitro methods are not
indicative of the probability of similar hybrids occurring by cross-pollination under natural conditions.
Even where there is an inter-specific hybridisation between B. napus and a related species growing in
proximity, poor vigour and high sterility in the hybrids will generally mean the hybrids and their
progeny will not survive in either an agricultural or natural habitat.
• In a post-doctoral study at the CRC for Weed Management Systems in Adelaide, 50 million seeds
from imidazolinone resistant wild radish hybridisation experiments were tested for hybridisation
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involving ALS resistance. Fewer than five (5) plants were determined as potentially resistant (10 ).
-5
Although not directly comparable, this is less than the figure of 10 determined by Steve Powles and
C. Preston of the CRC as the natural frequency in untreated populations for ALS resistant alleles in
annual ryegrass.
The closer the relationship between the parental genotypes, the greater the probability of successful
hybridisation and gene transfer. This means that the likelihood of out-crossing to a related weed
species is even lower than that for out-crossing to other canola varieties. Therefore, the chances of
successful, long-term survival and establishment of the gene in new hybrid-derived populations of
related species is even lower.
5.18 Managing out-crossing of Clearfield canola to related species
Out-crossing between canola varieties and between canola and related weeds is known to occur. For
this reason, management practices described here should be followed to minimise the likelihood of
out-rossing with Clearfield canola:
•
Control all Clearfield canola volunteers in the following year.
•
Control all Brassica weeds both in-crop and in adjacent sites such as fence lines before
flowering.
•
Where possible, avoid growing Clearfield canola in paddocks adjacent to other canola
varieties.
•
Best Management Practice is to not grow consecutive canola crops, regardless of variety.
•
Cover loads during harvest and transport to avoid dispersing seed.
5.19 Potential for out-crossing in Clearfield Maize
Maize in Australia is often grown in complex rotations of summer and winter crops in relatively
confined geographic areas. These systems often utilize a wider variety of management techniques,
including cultivation, knock-down and pre-emergent herbicides. Maize is not invasive, has relatively
low seed dormancy, low seed shedding and is a poor competitor during early seedling stage. These
factors decrease the potential for maize to become weedy.
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The Clearfield trait does not infer any additional advantages other than tolerance to Lightning
Herbicide and therefore Clearfield Maize will act in a very similar manner to non-Clearfield varieties
in the environment.
Maize is an open pollinated species and therefore there is potential for Clearfield varieties to crosspollinate with non-Clearfield varieties. However, given the relatively low potential for invasiveness of
maize in general, Clearfield maize is considered to show a low risk as a result of any outcrossing.
Maize has been shown to have the ability to produce fertile hybrids by outcrossing to other species.
However, other Zea species sexually compatible with Zea mays are not found in Australia and
therefore there is not potential interspecies target for outcrossing.
The overall risk of outcrossing of the Clearfield gene is Australia is extremely low.
5.20 Managing practices for Clearfield maize
The greatest risk in Clearfield maize is the potential for the development of resistance. This is
particularly the case in situations where there is the potential for rotations between maize and
Clearfield canola, Clearfield wheat/Clearfield Plus wheat and Clearfield barley are possible. In
these situations, whilst typically a different weed spectrum is being targeted (ie summer weed species
vs winter weed species) there is a still a higher risk which needs to be managed.
Whilst the risk of genetic transfer is extremely low, Best Management Practices to minimize risk in
Clearfield Maize are:
•
Control all Clearfield maize volunteers in the following year.
•
Where possible, avoid growing Clearfield maize in paddocks adjacent to other maize
varieties.
•
Avoid growing consecutive maize crops, regardless of variety.
•
Cover loads during harvest and transport to avoid dispersing seed.
•
Avoid using Group B herbicides in fallow situations where Clearfield maize crops are planned
to be grown in the following season.
•
Avoid growing Clearfield maize following a winter Clearfield crop.
•
Consideration should be given to the use of residual herbicides from alternate mode of action
groups [eg atrazine (Grp C), s-metolachlor (Grp K), pendimethalin (Grp D)] in order to reduce
weed populations.
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6.0 BASF Contacts
Sales Team
Contact Number
E-mail
Trevor Gillespie - National Sales Manager Crop
Protection
0418 162 705
[email protected]
Chris Ryan - Regional Sales Manager Southern
Region(WA, SA, VIC, TAS)
0400 090 276
[email protected]
Lachlan Broad - Area Sales Manager SA, VIC, TAS
0407 880 746
[email protected]
David Clegg - Area Sales Manager, WA
0408 630 641
[email protected]
Lindsay McRae - Regional Sales Manager Northern
Region (NSW, QLD, NT)
0438 033 887
[email protected]
Andy Byard - Area Sales Manager, Northern NSW, QLD
0407 880 472
[email protected]
Joel Murphy - Area Sales Manager, Southern NSW
0437 791 730
[email protected]
Southern Region (WA, SA, VIC, TAS)
Northern Region (NSW, QLD, NT)
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Contact your local Agricentre© for further information: agro.basf.com.au
Customer service Australia-wide: 1800 558 399
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© Copyright 2014 BASF Australia Ltd
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