Features Agronomy Insect Pests
European corn borer likes Canadian potatoes

Potato producers and researchers have seen increased evidence of the
European corn borer in New Brunswick, Prince Edward Island and Quebec,
but only in small pockets throughout the three provinces and there are
signs that the pest problem may be weakening.

Gilles Boiteau is an entomologist with Agriculture and Agri-Food
Canada’s Fredericton, New Brunswick research centre. He says the
European corn borer has always been a pest in eastern Canada, but until
the last six or seven years, it has never been an increasingly
predominant problem for potato producers. Sightings have increased and
problems in the potato field associated with the European corn borer
are also on the rise.

Previous to more focussed attention on the corn borer, Boiteau says it was common to blame the appearance of the corn borer in potato fields on the proximity of corn fields.
Producers were advised to plant their potato crops far from corn fields
to prevent the adult (moth) European corn borer from migrating into
potato fields.

Regardless, the corn borer has continued to appear in potato fields even after farmers have relocated
their corn crops. “This suggests they can do well on potatoes,” Boiteau
states. The increase, however, has been ‘very localized’ and varying between provinces, regions and even fields.
“There tend to be hot spots,” Boiteau says. “In Prince Edward Island it
seems to be a little more consistent, but it’s not as major a pest as
the Colorado potato beetle for example.”

Leaving plant debris in the field may increase chances of corn borer overwintering to the next season.

The same holds true in Quebec, says Serge Bouchard, a potato specialist
with Quebec’s Department of Agriculture, Fisheries and Food. Even with
the hot spots, Boiteau says the incidents of reported damage in
Atlantic Canada have decreased in the last two to three years. Boiteau
says even if there are some incidents of corn borer infestation, potato
plants are able to withstand a fair amount of pressure before yields
are reduced.

The European corn borer is a challenging pest to control, Boiteau says, but it is important that
producers keep it in check or the population could expand and get out
of control. Still, management of the corn borer can be like chasing a
shadow.

He explains that indistinct, brownish adult moths are usually found in
the vegetation surrounding potato fields. It has been determined they
move into the field at various times in the growing season to lay small
whitish egg masses on the leaves of the potato plant.

The small, almost
invisible larvae hatch and spend one day or so on the plant before entering the plant stem where they are hidden from view as they feed on the inside. Nearly invisible, yes, but the destruction can eventually be quite obvious. By the entry holes and the
inside of the stem being eaten away, the plant stalk is weakened and
could break over time.

Three reduced risk insecticides have recently been approved to help fight the corn borer. The new
chemistry, Boiteau explains, impacts the pest’s reproduction. Applied
to the plant, it is absorbed and ingested by the corn borer.

The European corn borer overwinters in the stems of potato plants left
in the field. Although common practice has been for producers to leave
plant debris over the winter to provide added ground protection,
leaving them could increase the chance of European corn borer infection
in spring’s new potato crop. Boiteau says producers have a balancing act and some have turned to technology for help. He notes a
stem crusher implement, developed by Dr. Christine Noronha at the
Charlottetown Research Centre of AAFC, that attaches to harvesters has
been shown to be effective at destroying corn borers and leaving winter ground protection in the fields at the same time.

Along with the near invisibility of the pest, the problem in the fight against the European corn borer is
still one of timing, Boiteau states. Finding the right time to apply
protection is tricky because eggs are laid during a period of weeks.
Some producers and research facilities use traps to try to gauge the
arrival of female moths, while others scout fields for numbers of egg
masses or numbers of entry holes on stems. Additional challenges arise
when summer temperatures cool, causing egg laying to slow down.

“It remains a very difficult task,” Boiteau explains. “You want to spray at the ideal time and this is quite a challenge with the corn borer.” Scouting fields, watching for any
evidence of the European corn borer and being mindful of control
methods are a farmer’s best defense against the pest. -end-