Prairie growers disappointed with the performance of their herbicides
this summer should search for answers to avoid similar problems in the
future.
Many producers voiced concerns over herbicides not doing as good a job
as usual.
Clark Brenzil, Saskatchewan Agriculture weed control specialist,
believes part of the problem arose from the temperature at the time of
herbicide applications, particularly in areas where crops and weeds
were stressed by heat and dry weather.
Heat-stressed weeds produce a thicker wax layer on the leaves. Also,
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the metabolism and transport mechanisms of plants, particularly cool
season crops, slow to the point where the plant stops growing. The
result is less effect from herbicide.
The likelihood of that happening was greatest in systemic products
because they have farther to go to reach their active site than contact
herbicides, Brenzil said.
Systemic chemicals have to overcome many obstacles, both outside and
inside the plants on their way to the target site, and have a limited
time to get there before they start breaking down or getting tied up in
other structures of the plant.
“I think probably the environment had a lot to do with the performance
of most herbicides this year,” Brenzil said.
A lesson learned for future years is that producers must be patient
when hot weather hits during spraying season.
When temperatures are 25-30 C during the daytime, it’s best to wait
until later in the day or earlier in the morning to spray, said
Brenzil. If temperatures soar above 30 “you might as well just find
something else to do for awhile or rest up for when spraying can
continue.”
There were days this summer when the mercury climbed above 37, and the
temperature was still around 30 at dusk.
Under those circumstances, it’s best to postpone spraying until at
least two days after the scorching temperatures have subsided, Brenzil
said.
That will give crops and weeds time to recover, limiting the likelihood
of damage to the crop and increasing the likelihood that the herbicide
will have the desired effect on weeds.
This year also showed it’s important to scout fields for signs of
problems soon after spraying so the cause can be more easily identified.
“We had a lot of questions about the performance of products in
August,” Brenzil said. “When it’s that late, it’s harder to diagnose a
problem.”
Brenzil recommends inspecting a treated crop about five days after a
herbicide application for signs of crop damage, which could indicate a
tolerance problem.
The crop should be scouted again two to three weeks after the
application to determine whether there was good weed control.
The cool spring this year delayed the emergence and development of
crops and weeds. The weather then shifted suddenly toward hot
temperatures, adding to the challenge of growing a crop and getting
good weed control.
It also made it difficult to know what was to blame when herbicides
failed to reach expectations.
“The easiest way to tell if there is a problem is to make sure to leave
a couple of small check plots in the field,” Brenzil said.
