“Across North America, horn fl ies
are still the number one pest bothering
cattle, and we need more options
for controlling them.”
It often helps to rotate, using a different
chemical every year or so, but there
are some regions around the country
where horn fl ies have resistance to
organophosphates and pyrethroids.
“Here in the Southeast we’ve been
using these products for 50 years, and
we have many populations of resistant
fl ies, yet there are still some producers
who get good control using the same
products that no longer work for their
neighbors. Some populations of horn
fl ies are still susceptible to these products,
especially if rotated. Stockmen
generally use pyrethroids for two years,
then organophosphates for three years
and then switch back again. Yet just
down the road there may be a different
population of fl ies and nothing is
working to control them,” she explains.
For stable fl ies, there is no effective
way to control them with chemicals
since they spend very little time on the
animal (compared with horn fl ies) and
breeding sites can be extensive. “We
want a simple answer, like spraying, but
there’s not enough insecticide in the
world to effectively spray through a hay
ring around a bale feeder. The organic
material binds up the insecticide and it
will never get down to where the maggots
are,” she says. Organic debris holds
moisture and creates the perfect habitat
for fl y production all summer.
Some herds have been using feedthrough
insect growth inhibitors (to
keep horn fl y maggots in the manure
from maturing) and are happy with
this strategy. If the herd is isolated
from other cattle — no fl ies coming in
from other places, this can work.
The traditional back rubbers, oilers,
and dust bags may be helpful in situations
where cattle have to go through a
gate or learn how to use them in a small
area. Cattle enjoy rubbing on these
because it gives some relief from horn
fl ies. “You have to recharge the oiler or
back rubber, however, and if the fl ies
have become resistant to that insecticide
it may not work,” Hinkle adds.
Biological controls like parasitic
wasps and naturally-occurring dung
beetles help break down manure pats
and reduce the number of fl y larvae
that survive and emerge as adults.
Other natural controls include birds
that eat fl ies or scratch through manure
pats looking for maggots. We’d have a
lot more fl ies without these allies.
Horn fl ies on a big ol’ bull.
JUNE / JULY 2020 I WORKING RANCH I 47