Herbicides
41
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Safety - page 25 • First aid - page 33 • Resistance management - page 41
Herbicide and Water Quality
Herbicide
Quality concern
Remedy
2,4-
D amine*
Mineralized water
Use a non-ionic surfactant like Agral 90
Achieve (tralkoxydim)
Mineralized water
Add ammonium sulfate (1% v/v)
Poast (sethoxydim)
Mineralized water
Add ammonium sulfate (1% v/v)
Roundup/Touchdown
Mineralized water
Add ammonium sulfate fertilizer
3
kg/100 L application solution
Roundup/Touchdown
Silty or dirty water
Filter water or use clean water
Select (clethodim)
Mineralized water
Add ammonium sulfate (1% v/v)
*
Note: 2,4-D Ester formulation is not affected.
Information primarily derived from F. A. Holm, J. L. Henry, D. W. Gruber and P. McMullan, 1995 Water quality effects on
phenoxy and ACCase inhibiting herbicides. Proceedings of the Weed Research/Symposium, University of Alberta.
The pH of water or water temperature can affect the
ability of some herbicides to stay dissolved in the spray
solution. To avoid these problems, the manufacturer will
suggest a specific order to add surfactant or mixtures of
products. For example, to mix the herbicide Horizon,
the herbicide is added first, followed by the surfactant,
Score, and all mixing is done under agitation. Other
water conditioners out there include Choice Weather
Master and N-Tank. Follow label recommendations for
mixing. Products cannot work unless they are dissolved
or miscible (capable of being mixed) in the water. Also,
if products are not in solution they can form a sludge in
the spray tank and block nozzles.
It is best to avoid using poor quality water if possible;
however, the following remedies can limit the loss of
herbicidal activity.
Pesticide Resistance
The Problem
Agricultural pests can develop resistance to fungicides,
herbicides or insecticides. Resistance occurs when
some pests survive a pesticide application; this part
of the population is naturally more tolerant to the
chemical. These individuals reproduce and create a
population that is resistant to the pesticide. Producers
should follow agronomic practices that both prevent
or minimize the development of resistance and
prevent the spread of existing resistant populations.
Since the first documented case of chickweed resistance
in the mid 1980’s, the numbers of herbicide resistant
weeds, fungicide resistant diseases and insecticide
resistant bugs have increased and the area infested by
them continues to grow. At present in Alberta, more
than 10 weed biotypes are resistant to chemicals from
six herbicide groups. Potato blights are known to have
developed resistance to common fungicides. Some
insect pests are resistant to the
Bacillus thuringiensis
,
a
common biopesticide. In addition, some resistant pests
are resistant to more than one pesticide group (see table
below). It is essential that producers be able to identify
these resistant pests and take action to minimize or
prevent the development of resistance on their farms.
How to identify herbicide resistance
Investigate all areas of the sprayed field where weed
control did not occur. Rule out other factors that
might have affected herbicide performance including
mis-application, spray misses, unfavorable weather
conditions, herbicide application at an improper leaf
stage and weed flushes after application. If resistance
remains a likely possibility, check for the following:
•
Are other weeds listed on the product label
controlled satisfactorily?
•
Is herbicide failure patchy with no reasonable
explanation?
•
Did the same herbicide or herbicide group fail in
this area of the field in the previous year?
•
Do weeds show herbicide injury symptoms such as
root pruning by a Group 3 herbicide or yellow/
purple coloration caused by Group 2 applications.
Resistant weed biotypes will not show these typical
injury symptoms.
•
Do field histories indicate extensive use of the
same herbicide (or herbicide group) year after
year?