Seed & Chemical
Foliar vs. in-furrow
By Top Crop Manager
Use label rates to delay resistance to products
The days when potato farmers will automatically choose an in-furrow or seed
treatment insecticide to control Colorado potato beetles and aphids may be drawing
to a close. Growers now have the option to choose a new foliar insecticide to
control these pests. They either can spend the money for season long control
with an in-furrow product or choose a lower cost foliar product like DuPont's
Assail that provides two to three weeks of Colorado potato beetle control. It
is a far cry from the late 1990s when insecticide resistance left growers with
"In the 1990s there was a movement away from widespread use of foliar
applied materials to in-furrow applications," says Dr. Robert Coffin, crop
specialist with Cavendish Farms. "Colorado potato beetle had built up widespread
resistance to a number of the commonly used foliar insecticides, so a lot of
people were anxious to find something that was dependable. Admire worked very
well when it came on the market and it quickly became the most commonly used
insecticide. Now we're seeing people moving back to foliars."
People are switching back for a variety of reasons: cost, insecticide rotation
and an increasing problem with European corn borers, particularly in Prince
Edward Island, New Brunswick and Maine. Since in-furrow treatments do not control
corn borers, Coffin suspects the increase in population was a direct result
of its use. Prior to widespread adoption of in-furrow treatments, producers
had inadvertently been keeping corn borer numbers under control with their foliar
insecticides used to control potato beetles. After everyone switched to in-furrow,
they suddenly started to notice significant corn borer damage.
"In Prince Edward Island, there has been a dramatic increase in corn borer
populations since the widespread adoption of the in-furrow insecticides,"
says Rachael Cheverie, integrated pest management specialist with Prince Edward
Island's Department of Agriculture, Fisheries and Aquaculture. "Producers
who put down in-furrow insecticide for Colorado potato beetle are now actually
having to put on one or two sprays of foliar insecticide for corn borer on top
of that. This gets quite expensive."
With foliars again an option in many cases, Cheverie recommends taking an integrated
pest management (IPM) approach for potato beetle control in fields deemed to
be at lower risk of a severe outbreak. In these fields, producers should start
by scouting their fields to find out what the pest levels are and then use threshold
levels to determine whether or not they are there in enough numbers to warrant
The main disadvantage to using an in-furrow or seed treatment product is that
the user has to guess what type of pests are there and determine how much money
can be spent to control them in advance. Since an application is only based
on a prediction, instead of an actual outbreak, there is always a risk of spending
money on something that is not necessary.
"The question is, do you need season long control or will a single foliar
application of Assail in June be all that is needed?" Alex Crouse, specialty
product manager with Dupont, says. "At the end of the day it comes down
to money, it's the difference between spending $70 to $80 dollars an acre and
spending $19 to $36 an acre."
"In some potato growing areas you are reasonably certain of having some
insect pressure," Coffin says. "However, with changing conditions
you may not have enough pressure to justify the cost. On the other hand, people
growing seed potatoes worry about the spread of virus disease by aphids and
since in-furrows give some suppression of aphids, they use it as a tool to reduce
the spread of viruses."
Controlling insects and disease in potatoes starts with crop rotation. "At
least a three year rotation is needed to break up pest and disease cycles in
the soil," Cheverie says. "It prevents excessive numbers of insects
from building up in a field over time. Next, look at both the field history
and the history of fields around it. Have you previously had a huge problem
with Colorado potato beetles or corn borer? What products have you been using
for the last number of years in that area?"
There is more to rotating insecticides than just changing brands. Assail and
Admire, for example, are in the same chemical family (chloronicotinoids). Producers
need to alternate insecticides with different modes of action. "We don't
recommend people use Admire in-furrow and then use Assail as a foliar the same
season because you're not rotating the chemical families," Crouse says.
"We are trying to encourage people to look at their pest pressure and spectrum
before committing to an in-furrow application. In some areas, we've seen growers
who have not had enough Colorado potato beetle pressure to even warrant an in-season
insecticide application. It all comes down to flexibility and saving money."
If you are unsure which product to choose, start by checking the product label.
"It's important for the producer to take the time to sit down and carefully
read the labels," Coffin says. "Look at what claims are made, look
at what insects the product will or will not control and look at how long it
will remain effective. If the label says to use so many kilograms or so many
millilitres of the product, don't cut the rate. Sometimes people say I can cut
the rate and maybe they might get away with it for a year or two, but all it
does is encourage resistance. Following label instructions is fundamental."
Cheverie recommends saving in-furrows for the fields that most need it, fields
with heavy potato beetle pressure and fields close to waterways since there
is much less risk of agricultural run-off with an in-furrow product. In areas
where the population pressure is a bit lower, use the newer foliar products
and rotate chemistries for resistance management.
"Resistance is a big concern," Cheverie says. "I understand
that when Admire first came out, there was a huge resistance problem with everything
that was already registered. Now there are other safe, good options out there
that will allow you to build a spray program to control both the Colorado and
the corn borer. In-furrows are great but now that we have other options, we
should think about saving the in-furrow treatments for when we really need them."