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Tank-mixing herbicides with fungicides and insecticides

Pesticide companies working to expand tank-mix options.


November 19, 2007
By Bruce Barker

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Every spring, Syngenta's technical crop manager, Edward Thiessen receives phone
calls from farmers asking about tank-mixing herbicides with fungicides or insecticides.
While several tank-mixes are currently registered, Thiessen explains that getting
registration is difficult.

"There tends to be peaks and valleys in disease and insect outbreaks,
so it is hard for companies to get enough data together to apply for registration,"
says Thiessen. "The biggest difficulty is getting enough performance data
to prove the tank-mix works."

Thiessen says Syngenta invests in some research each year to exploring these
tank-mix options. The company has been successful in getting some tank-mixes
registered, such as a Tilt tank-mix with herbicides like 2,4-D or Buctril M
or Horizon. Tilt is a fungicide used to control leaf diseases, while 2,4-D and
Buctril M control broadleaf weeds. Horizon is a grassy weed herbicide.

Bayer CropScience also works on tank-mix research every year. In 2006, the
company was successful in developing what Shaun Corneillie, fungicides portfolio
manager with Bayer, describes as the first three-way tank-mix registrations
in Canada. The tank-mix registration allows a mix of the fungicide Stratego
250EC with Puma Super and Buctril M or with Puma Super and Refine Extra in wheat.

"The research is difficult to do because you have to prove efficacy on
all the products," explains Corneillie.

Proper crop and pest timing important
Tank-mixing a fungicide to control sclerotinia and an insecticide to control
a pest such as diamondback moth, lygus bug or bertha armyworm is not uncommon.
However, farmers have to be careful about the timing so that both products provide
the optimum control. If the timing is not good for both, a split application
might be better.

Corneillie agrees that timing can be an issue. He says the Stratego tank-mix
can be useful if the grower is planning on two fungicide applications. He explains
that the early season fungicide application, tank-mixed with a herbicide, provides
early season canopy disinfection to suppress disease development, while a second
application of Stratego around heading will protect the crop against later disease
development. However, he cautions that early application of a fungicide is not
recommended if only one application is planned.

"If you're just planning on doing one application of a fungicide to control
leaf disease in wheat, you're better off going at heading stage than tank-mixing
with a herbicide and going earlier," says Corneillie.

Do not go off-label
Jim Broatch, an insect pest management specialist with Alberta Agriculture and
Food, agrees that farmers need to be aware of timing issues when looking at
tank-mixing herbicides, fungicides and insecticides. He also cautions that going
off-label to mix up a tank-mix cocktail is not recommended and brings significant
risks.

"The first risk is a chance of a chemical interaction that could result
in the pesticides precipitating out and plugging the sprayer nozzles,"
explains Broatch. He also cautions that an interaction could cause one or both
products not to work properly.

If the tank-mix is not registered, then either the company has not been able
to compile all the registration data, or they have found the tank-mix causes
antagonism that results in a lack of effectiveness. Either way, if you are mixing
up your own special tank-mix, you lose the right to have the pesticide company
investigate the lack of performance.

Even worse would be using a product that is not registered and leaves residues
in the grain. Importers have the right to reject shipments of grain that have
detectable pesticide residue that do not meet their criteria. That is why the
entire agricultural industry must work to ensure that only registered products
are used and pre-harvest intervals are observed.

Broatch says another issue to look at is whether the registered tank-mix is
really needed. For example, are economic threshold levels being used to decide
if an insecticide is needed, or is the use of the insecticide just for cosmetic
purposes? "If the insect isn't at the economic threshold level, you can
be doing more harm than good by also controlling the beneficial insect predators
that might keep the insect pest at bay."

Thiessen says where tank-mixes get tricky and the legalities a bit cloudy is
multiple tank-mixing and where some tank-mixes are only registered by one of
the companies. For example, he says the Horizon label has Decis insecticide
as a registered tank-mix, as well as a Horizon and Buctril M tank-mix. What
is not clear from the labels, though, is whether all three products can be tank-mixed,
which could offer one-pass control of weeds and an insect like grasshoppers
in wheat. Plus, the Decis label has Buctril M as a registered tank-mix, but
not Horizon.

Manitoba Agriculture and Saskatchewan Agriculture and Food both include a pesticide
tank-mix chart in their annual Guide to Crop Protection. While the chart outlines
what product is registered and who registered it, it does not provide detailed
information about multiple tank-mixes which can only be found on the label or
from the pesticide companies.

"The best advice I can give is for growers to call the company's information
lines to check on the registered tank-mixes. One company may have the registration
on its label, but not the other. In that case, the company with the registration
assumes responsibility for the product performance," explains Thiessen.

Ultimately, two and three-way tank-mixes will not be the dominant use of pesticides,
even if many more registrations are obtained. But, when the timing is correct,
tank-mixing herbicides with insecticides or fungicides can cut out a second
sprayer pass, saving time and money. -30-