PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
RESISTANCE.
WHAT IS
RESISTANCE?
Australia has a
very high level of
herbicide resistance
Glyphosate resistant
weeds have been
confirmed in Australia,
eg ARG, awnless
ryegrass and
liverseed grass.
When growing
herbicide-resistant
crops take care that
weeds in the crop do
not become resistant
to the herbicide being
used.
RESISTANCE
MANAGEMENT
STRATEGIES
Classification by
Croplife Australia is
according to how
the pesticides kill
the insect, fungi
and weeds and is
used for resistance
management.
It does not indicate
toxicity,
that some groups are
more toxic than
others as indicated by
the signal headings
on their labels (see
page 237).
Applications may
fail for reasons
other than
resistance, eg
Incorrect identification of
the weed.
Wrong herbicide may
have been used.
Applied at wrong time.
Weather is unsuitable for
application.
Equipment not calibrated
properly.
Application errors, wrong
rates, nozzles, etc.
If resistance is
suspected, resistance
testing can be arranged.
Herbicide resistance is the ability of a weed to survive a herbicide rate that would
normally control it. If resistance develops, other herbicides, or more expensive, or less
effective control methods, may have to be used. Once developed, herbicide resistance
can persist for many years. Keep accurate records of herbicide usage.
In 2005, in 40 countries, there were at least 178 documented cases of grass and
broadleaf species of weeds resistant to herbicides belonging to most mode of action
groups, including glyphosate. In Australia, weeds which are resistant to at least one
mode of action group of herbicides include annual ryegrass (ARG, Lolium rigidum),
wild oats (Avena spp.), barley grass (Hordeum leporinum), wild radish (Raphanus
raphanistrum), Indian hedge mustard (Sisymbrium orientale), common sowthistle
(Sonchus oleraceus), prickly lettuce (Lactuca serriola) www.weedscience.org
Cross-resistance. ARG shows what is known as cross-resistance which means that
ryegrass which develops resistance to one herbicide will develop resistance to
herbicides with similar modes of action.
Conditions favouring herbicide resistance.
– Most weed populations contain a small number of resistant plants able to survive
an application of a particular herbicide. Repeated use/over-use of one herbicide, or
other herbicides with the same mode of action, will kill susceptible weeds, but allow
survivors to grow and multiply, these surviving resistant weeds become common.
– Levels of resistant weeds depend on whether the grower uses non-chemical
methods, as these influence herbicide group selection and application frequency.
– In Australia ARG resistance is the world’s worst case of herbicide resistance. There
are many reasons for this. Arguably ARG was once regarded as a valuable pasture
grass (60 million acres of it). When these pastures were converted to crops, ARG
became a weed of crops grown under minimum tillage and a reliance on herbicides
for weed control. Also farming in Australia is extensive, with lower yields, no
subsidies, and so lower rates of certain herbicides are applied than in other countries.
Commercial herbicide resistance testing services operate for a range of
grass and broadleafed weeds. Weed seed is collected at certain times of the year and
screened for resistance to herbicides using various techniques. The number of resistant
seeds per square meter can be monitored over a period of time to determine whether the
resistant seed bank is increasing or decreasing. The effect of various cropping systems on
the replenishment of resistant seed can also be determined.
The application of herbicides must be part of an IWM program (page 429) which
includes non-chemical methods, eg maximizing crop competition (pages 432, 433).
Herbicide Resistance Management Strategies.
– CropLife Australia has classified herbicides into mode of action resistance
groups which indicate the mode of action of the herbicide on a metabolic process
in the weed, ie how it kills or suppresses the weed (page 450, Table 72).
Contact Croplife Australia for updates on classification and click on Resistance
Management:
www.croplifeaustralia.org.au/
– To minimize the development of resistance and prolong the life of existing
herbicides, observe ABC…. groups on commercial herbicide labels. Follow
resistance warnings. Rotate herbicides between different modes of action as
recommended. Home garden products available from garden centres are
not required to have herbicide mode of action groups on them.
– CropLife Australia has also prepared Specific Guidelines for particular groups of
herbicides and a List of Herbicide Resistant Weeds in Australia and Protection
Guides for some crops, eg rice. There are links to the Glyphosate Sustainability
Working Group, the Integrated Weed Management Manual and the Monsanto
Australia’s Roundup Ready Flex® Cotton Technical Manual.
Follow label instructions and warnings. which include resistance strategies.
Application of some herbicides for control of some weeds is restricted in order to
prevent or delay the likelihood of resistance developing. “Example” and “Company”
are used in the following resistant weeds warning notice to avoid using specific
herbicide or company names.
RESISTANT WEEDS WARNING
GROUP M HERBICIDE
Example is a member of the Glycines group of herbicides. Example has the inhibition of
EPSP synthase mode of action. For weed resistance management Example is a Group M
herbicide. Some naturally occurring individual weed biotypes resistant to Example and
other Group M herbicides may exist through normal genetic variability in any weed
population. The resistant individuals can eventually dominate the weed population if these
herbicides are used repeatedly. These resistant weeds will not be controlled by Example
or other Group M herbicides. Since occurrence of resistant weeds is difficult to detect prior
to use, Company accepts no liability for any losses that may result from the failure of
Example to control resistant weeds.
Growers must practice preventative resistance management strategies………
Weeds - Integrated Weed Management 449