| The positive identification
of bladder ketmia, a weed closely related to cotton in the family Malvaceae,
is important to ensure that the correct management strategies are employed
for the particular variety or type.
The Malvaceae family also includes species such as anoda weed, velvetleaf
or swamp Chinese lantern, native rosella, marshmallow and spiked malvastrum.
All are common summer growing weeds, with the exception of marshmallow.
The various varieties of bladder ketmia (wide leaf and narrow leaf)
are widespread throughout the cotton industry. In a recent survey by
Ian Taylor, NSW Agriculture (ACRI), conducted from Hillston in southern
NSW to Emerald in central Queensland, bladder ketmia was found to be
the most troublesome and widespread weed, infesting nearly 85 per cent
of the cotton properties surveyed.
While individual plants are not overly competitive, bladder ketmia plants
often occur in dense stands that can cause considerable localised yield
losses. Bladder ketmia is extremely difficult to control, most notably
because there are a number of seedling flushes throughout the season
— typically following irrigation and rainfall.
The weed also has prolific seed production, and since it is related
to cotton, there is a limited range of herbicides that can be used without
the risk of crop injury.
Different bladder ketmia varieties
There are two different varieties of bladder ketmia, generally distinguished
by their leaf shape — wide leaf bladder ketmia and narrow leaf
bladder ketmia (see photos). Wide leaf bladder ketmia is generally found
in the hotter, western and northern cotton areas, while narrow leaf
bladder ketmia is found mainly in the cooler, eastern areas (see map).
Both varieties are commonly found around the line on the map.
Wide leaf bladder ketmia (Hibiscus trionum
var. vesicarius)
Wide leaf bladder ketmia is an erect annual plant, five to 150 cm tall
with waxy, green leaves that are around 90 to 100 mm long and 70 to
80 mm wide. There are two types of wide leaf bladder ketmia. Both have
cream or yellow petalled hibiscus-like flowers, but are differentiated
by the colour found at the centre of the flower.
One type of wide leaf bladder ketmia has flowers with a yellow centre
(see photos, page 52). It is commonly found throughout NSW and southern
Queensland — for example in the Macintyre valley, on the Darling
Downs around Dalby and Jimbour and at St George.
The other type of wide leaf bladder ketmia has flowers with crimson/red
centres and is commonly found throughout central and western Queensland.
It is likely that both types co-exist in a number of areas as they have
been found growing together near Jimbour on the Darling Downs and in
the St. George irrigation area.
Narrow leaf bladder ketmia (Hibiscus trionum var. trionum)
Narrow leaf bladder ketmia is a semi-prostrate to erect annual plant,
five to 130 cm tall with leaves that are around 70 mm long and 90 mm
wide (see photo, page 54). Plants tend to be shorter than wide leaf
bladder ketmia and have more deeply divided leaves. The flowers of narrow
leaf bladder ketmia have cream coloured petals with a deep purple centre.
Narrow leaf bladder ketmia is common in eastern and southern NSW and
on the Darling Downs in Queensland. It is probably the only variety
of bladder ketmia found in the Gunnedah area and to the east of Dalby.
It is commonly found growing with the yellow centre flower type of wide
leaf bladder ketmia in the Namoi, Macquarie and Lachlan valleys and
with both wide leaf types around Jimbour on the Darling Downs.
Why are these differences important?
Timely management
It is important to recognise the differences between both varieties
of bladder ketmia to ensure that management is done in a timely fashion
when the plant is vegetative and easier to kill, and so that herbicide
selection is optimised.
For example, narrow leaf bladder ketmia can flower and produce mature
seed faster than the wide leaf types and needs to be managed within
the first four weeks of emergence, before flowering occurs. Even within
the wide leaf bladder ketmia types, timing is important. For instance,
the vegetative phase of the yellow flowering type is five weeks whereas
it is nearly six weeks for the red flower type, giving one to two weeks
longer to manage plants.
Depending on the type of wide leaf bladder ketmia, mature seed is set
within 53–61 days, (Table 1). Each mature seed head has an average
of 33–34 seeds and between 0–199 (an average of 67) seed
heads are produced over the annual lifecycle of this plant. This results
in an average of 2300 new seeds added to the soil for each mature plant.
There appear to be other differences between the two types of wide leaf
bladder ketmia, most particularly in leaf size, the times required until
flowers are produced and seed heads matured, and the number of mature
seed heads produced.
In narrow leaf bladder ketmia, flowering and seed set occurs more rapidly
with flowering within 30 days of plant emergence and mature seed set
within 46 days (Table 1). Each mature seed head has an average of 34
seeds, and between 0–395 (an average of 164) seed heads are produced
annually. This results in an average of 5600 new seeds added to the
soil for each mature plant.
It is important to note that the figures presented above are glasshouse
averages and that times may vary in the field. In particular, plants
may go to seed quicker under shorter daylength conditions, for example,
towards the season’s end. Research is still being conducted to
see if this is the case.
Both types of bladder ketmia need to be monitored throughout the season
to reduce or prevent seed set, not only because flowering and seed set
occurs relatively quickly, but also because there are a number of emergence
events throughout the season after rainfall and irrigation. Reducing
seed set is particularly important because a relatively light infestation
of two plants per square metre can result in between 46 and 112 million
new seeds added to the soil seed bank per hectare every year for wide
and narrow leaf bladder ketmia respectively.
Bladder ketmia seed is strongly dormant and will be an issue for well
over five years. Trials are continuing to determine if there are differences
between the varieties. With strong seed dormancy it is easy to see that
once seed set has occurred in one year, it is very difficult to reduce
the weed problem that bladder ketmia causes for many years thereafter.
Herbicide control
Bladder ketmia is difficult to control using the current herbicide range.
It can only be effectively managed with good integrated weed management
(IWM) including cultivation, chipping, good farm hygiene and herbicide
applications in fallow and in-crop.
Although herbicide applications are only part of an IWM program, there
are a number of options available. The following information forms part
of a series of best bet management recommendations in WEEDpak, obtained
from interviewing a number of cotton growers and consultants.
Prior to planting, glyphosate and oxyfluorfen, or paraquat/diquat may
be used, followed by either diuron or fluometuron and prometryn at planting.
Roundup Ready (RR) herbicide should be used in RR varieties applied
over-the-top (up to the fourth true leaf stage), then an early lay-by
of prometryn and/or diuron depending on the herbicides already applied.
Season long management is needed.
Varietal differences may result in differences
in management
Knowing the difference between the bladder ketmia varieties can also
influence herbicide choice in some situations. For example, Scott Wallace,
a former University of New England student found that while glyphosate
(510 grams per litre of active ingredient) applied at label rates (1.35
litres per hectare) to adult plants that were in the early stages of
flowering and producing green seed heads achieved good control of both
varieties, these applications were more effective on the wide leaf variety.
This result fits well with growers’ experiences of controlling
both varieties of bladder ketmia in Roundup Ready crops.
Conclusion
Bladder ketmia is a widespread and troublesome weed found throughout
the Australian cotton industry. It is important to correctly identify
the different varieties and types of bladder ketmia to ensure timely,
season-long management.
Narrow leaf bladder ketmia can produce mature seed within six weeks
of emergence and requires prompt management. The wide leaf bladder ketmia
types (with either yellow and red centre flowers) require management
within eight to nine weeks to prevent seed production.
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