Loch, D. S.

University of Queensland eSpace

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The Australian
Turfgrass
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Know-how for Hotticuiture'"
28th Annual Australian Turfgrass Conference Proceedings Melbourne - 2012
28th Australian
Turfgrass Conference
Proceedings 2012
1
28th Annual Australian Turfgrass Conference Proceedings Melbourne - 2012
LIFE AFTER MSMAlDSMA: WHAT FUTURE OPTIONS DO WE HAVE
FOR GRASS WEED CONTROL IN TURF?
Don S. Loch
GeneGro Pty Lld and The University of Queensland
Introduction
The ability to remove of grass weeds selectively from warm-season turfgrasses has largely
been restricted to green couch (Cynodon dactylon) and its hybrids where the organoarsenate
herbicides MSMA (monosodium methanearsonate) and DSMA (disodium methanearsonate)
have been routinely used for this purpose during turf production and facility maintenance.
However, these chemicals have been under scrutiny from environmental agencies for several
years, and are now scheduled for withdrawal in the US by the end of 2013. In other turfgrass
species, the lack of any registered selective grass herbicides already means that annual and
perennial grass weeds (which often include green couch) have to be removed by non-selective
spot-spraying with glyphosate or by manual rouging of the grass sward. This adds considerably
to production and maintenance costs, and may still result in some contaminated turf reaching'
the market.
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The final withdrawal of MSMA and DSMA will be a 'game changer' for turf producers and turf
managers used to taking the easy option of MSMAlDSMA to control other grasses in green
couch. On the one hand, other turfgrass species for which effective alternative weed control
measures can be identified could become more popular in the marketplace. On the other hand,
alternative chemicals to control other grasses in green couch must be sought as a matter of
urgency. In a 2-year project (#TU09009) funded by Horticulture Australia Ltd using the Turf Levy
and matched funds from the Australian Government, the first steps were taken towards
identifying future opportunities through each of these alternative strategies.
Year 1 (2009/10)
The first strategy - looking for new opportunities with grasses other than green couch -
screened 11 turfgrasses from 9 different warm-season species against 7 different graminicides
in 2009/10 to assess their relative tolerances and susceptibilities to these chemicals. The
grasses trialled were:
• Axonopus compressus (broad leaf carpetgrass);
• Cynodon dactylon (green couch);
• Cynodon dactylon X transvaa/ensis (hybrid green couch);
• Digitaria didactyla (blue couch);
• Eremochloa ophiuroides (centipede grass);
• Pennisetum clandestinum (kikuyu grass);
• Stenotaphrum secundatum (buffalo grass) - two cultivars from different genetic races;
• Zoysia japonica (Japanese lawngrass) - two cultivars of different leaf texture and origin;
and
• Zoysia matrella (Manila grass).
The 7 graminicides initially trialled (fluazifop, fenoxaprop, haloxyfop, quizalofop, metamifop,
sethoxydim, and clethodim) in Year 1 (2009/10) came from two different chemical groups, the
arylphoxypropionates (commonly called the 'fops') and cyclohexanediones (commonly known
as the 'dims'). Collectively, both groups are classified by the Herbicide Resistance Action
Committee (HRAC) into their Group A because they have the same mode of action via a
specific form of an enzyme, acetyl-CoA carboxylase (ACCase), found only in grasses. ACCase
catalyses the first step in fatty acid synthesis, which is essential for building the new membranes
required for cell growth. A heteromeric form of ACCase, insensitive to Group A herbicides, is
found in broad leaf (dicotyledonous) plants but is absent from grasses. Grasses instead contain
28th Annual Australian Turfgrass Conference Proceedings Melbourne - 2012
a homomeric form of ACCase, which is sensitive to the fops and dims. Hence, ACCase inhibitor
herbicides typically show good selectivity between grasses and broad leaf plants, because the
herbicide-insensitive heteromeric ACCase enables fatty acid synthesis to continue in broad leaf
plants in the presence of these herbicides.
In the case of grasses, different species show differential tolerance and susceptibility to the
various Group A graminicides, which can then be exploited to control certain other grasses in
tolerant species. In the present studies, the 7 graminicides initially selected for trial were those
with potential activity on established perennial grass weeds (and green couch in particular).
Other fops and dims with activity only on annual or seedling grasses were excluded.
Fifteen herbicide treatments were applied to each of the 11 turfgrasses: an unsprayed control
treatment plus 1X and 2X rates of each of 7 graminicides. The 1X rates of herbicide were based
on label rates for the control of established perennial grass weeds, and all treatments included
recommended label rates of adjuvant. Treatments were assessed progressively by phytotoxicity
ratings for each pot and by a dry matter harvest 26 days after spraying (das). The pots were
then allowed to recover before clipping them again 60 das and re-applying herbicide treatments
again 69 days after the first application. These treatments were again assessed progressively
by phytotoxicity ratings of each pot and by a dry matter harvest 27 days after the second spray
application.
Both sethoxydim and clethodim were safe to use on centipede grass (which confirms US
experience) and caused only temporary stunting of the zoysias. However, clethodim was far
more effective than sethoxydim in controlling potential perennial grass weeds (the green
couches, kikuyu and blue couch).
Within the fops, fenoxaprop had relatively less effect on all grasses, including potential
perennial weed species (the 2 green couches and kikuyu). Grasses sprayed with fenoxaprop
also started to recover after about 2 weeks, as was also seen with quizalofop. In contrast,
stunting of growth with fluazifop and haloxyfop continued through the second month allowed for
recovery, except for blue couch where full recovery from fluazifop was seen much earlier.
The overall objective was to be able to incorporate the more effective of these herbicidal options
into future management strategies, specifically for use with turfgrass species other than green
couch which all of the chemicals trialled control to a greater or lesser degree. Therefore, based
on results from the first year screening trials, the 4 most promising herbicides in terms of
selectivity and efficacy (viz., fluazifop, haloxyfop, metamifop, and clethodim) were short-listed
for more detailed work during 2010/11 focusing on sequential spray applications and mixtures
with other chemicals (triclopyr, fluroxypyr, aminopyralid, cyhalofop) to improve grass weed
control and crop safety. While quizalofop was dropped at this stage, it remains an option for
spraying late in the growing season to enable recovery before winter when cold stress appears
to exacerbate the phytotoxic effects of the more persistent chemicals.
Year 2 (2010/11)
Group A ± Group 0 Herbicides. In Year 2 (2010/11), two separate experimental designs
(each with 4 replications) were imposed within each of the 11 grasses. The first of these was
sprayed twice and cut twice to determine dry matter yields 28 or 29 das; it was designed to look
separately at the effects of each of the additives from HRAC Group 0 (triclopyr, aminopyralid,
aminopyralid+fluroxypyr) used with Group A herbicides in the second experiment in which the
effects of Group A herbicides alone or mixed with Group 0 herbicides (mainly triclopyr). The
latter experiment was sprayed twice (0, 28 days) with only one dry matter harvest 56 days after
the first application date; 3 different sets of treatments were also imposed on different groups of
grasses, reflecting their different tolerances and susceptibilities as determined in Year 1.
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28th Annual Australian Turfgrass Conference Proceedings Melbourne - 2012
The use of triclopyr alone was strongly phytotoxic to the green couches, kikuyu, blue couch and
broad leaf carpetgrass. In contrast, the aminopyralid treatments had virtually no effect, other
than some stunting of growth on the 3 zoysias following the second application. The
aminopyralid+fluroxypyr product was only applied to four species (kikuyu, blue couch, broad leaf
carpetgrass, centipede grass), but caused visible phytotoxic damage and significant stunting of
growth in all of these, particularly after the second application; this probably reflected the
fluroxypyr component rather than aminopyralid based on its lack of effect on its own.
Fluazifop provided very effective control of the green couches and kikuyu, particularly after a
second follow-up application 28 days after the first application. The addition of triclopyr as a
'safener' relieved much of the discoloration and stunting of the zoysias from fluazifop alone, and
was also even more effective in controlling the green couches. With buffalo grass, the addition
of triclopyr also gave a very positive safening effect, stunting both cultivars temporarily but not
killing them. With blue couch, however, the addition of triclopyr increased the level of
phytotoxicity; fluazifop alone would therefore be the safer treatment to use with blue couch.
Clethodim was marginally less effective than fluazifop in terms of killing the green couches, but
it provided quite effective control of these perennial grass weeds, particularly after a second
follow-up application 28 days after the first application. Clethodim was extremely safe to use
with centipede grass, so much so that there was no discernible advantage from adding triclopyr
to the spray mix.
Metamifop was less effective than the previous graminicides in controlling the green couches,
so its potential role with tolerant or partially-tolerant grasses (zoysia, kikuyu, broad leaf
carpetgrass, and possibly blue couch) may be restricted to controlling annual grass weeds at
lower application rates. The addition of cyhalofop as suggested in the Korean literature
improved control of the green couches somewhat, but at the same time greatly increased its
level of phytotoxicity to the more tolerant species.
Flazasulfuron. As an additional extension to the original project, the alternative strategy aimed
at controlling other grasses in green couch was initiated in 2010/11 to look also at the efficacy of
flazasulfuron on all 11 turfgrasses. Flazasulfuron - a HRAC Group B sulfonylurea herbicide -
was developed by ISK in Japan in 1989 where it was initially used in zoysia golf courses; it is
now registered in a number of countries around the world for use in a diverse range of crops,
including sugarcane, tomatoes, grapes, pastures and turf. In March 2010, flazasulfuron
(Katana") was released for turf use in the US, including the removal of other grasses from
bermudagrass (green couch).
Flazasulfuron (at 1X and 2X rates) was added to the second year experiment looking at the
effects of the Group 0 herbicides (triclopyr, etc) alone. While it proved to be safe on the green
couches, zoysias and some buffalo grass varieties, flazasulfuron did not completely control blue
couch even after a second follow-up application (Plate 1).
Where To From Here?
Promising herbicide strategies for grass weed control based on the use of fluazifop ± triclopyr
have been developed for blue couch, zoysia grasses and buffalo grass. These now need to be
trialled and their efficacy and safety confirmed across a wider range of cultivars within each of
these species groups so that registration for commercial use can be made on a cultivar-by-
cultivar basis.
Flazasulfuron, by contrast, is not yet registered in Australia for any commercial use. If and when
this happens, it could have a wide variety of uses, not least being the control of weedy
Sporobolus species (e.g. Parramatta grass, giant rat's tail grass). While flazasulfuron could
clearly fill a very useful niche for the Australian turf industry, the present studies indicate that
alternative chemicals still need to be identified for effective blue couch control in green couch.
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28th Annual Australian Turfgrass Conference Proceedings Melbourne - 2012
Plate 1. Effect on blue couch of spraying twice at monthly intervals with flazasulfuron:
flazasulfuron 1X (centre) and 2X (right) rates compared with the unsprayed control
treatment (left) (28 days after second spray application).
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Life after MSMA/DSMA: what future options do we have for grass weed control in turf?

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Life after MSMA/DSMA: what future options do we have for grass weed control in turf?

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