Dr. Dave
Smitley
Department
of Entomology
Michigan
State University
There
is a growing concern among entomologists and other agricultural scientists
about the undesirable impacts of imidacloprid and other nicotinoid insecticides
on the health of honey bee colonies, and native bees. Nicotinoid insecticides are widely used on agricultural
crops to control destructive insects.
They are also used on golf courses and home lawns to control white grubs
and other turfgrass pests. A recent
study conducted in Kentucky by Dr. Dan Potter provides some useful information
for how to avoid negative effects on bees that forage in treated lawns (http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0066375). The results of this study can be summarized
as follows:
1.
Turf without any flowering weeds is not likely to be harmful to bees even
immediately after a nicotinoid insecticide application because it is unlikely
that bees will be present on the turfgrass.
Avoiding spray drift to surrounding flowering plants is advised.
2. Applications of clothianidin (a nicotinoid insecticide
used extensively on turfgrass) to turfgrass with clover in flower was harmful
to bumble bee colonies foraging on the clover.
However, if the lawn was mowed just before or immediately after
clothianidin was sprayed, so that there were no sprayed flowers present, there
was no harmful effect on the bumble bee colonies. Also, no harmful systemic effect was observed
when the clover began to bloom again after clothianidin was applied, as long as
the new flowers were not present when the lawn was sprayed. In the discussion of these results Dr. Potter
notes that more research is needed to address the long-term effects on bees
throughout the growing season after the uptake and translocation of nicotinoid
insecticides by clover and other flowering weeds.
 |
| White clover flowering in a low maintenance turf. |
3.
Chlorantraniliprole, a new turf insecticide with a different mode of action,
did not have any harmful effects on the bumble bee colonies under any
conditions.
Considering recent research on the impact of imidacloprid on
honey bees, and the results of the recent study summarized above, I recommend
that if a lawn with weeds in flower needs to be treated for grubs, that the
homeowner or lawn care professional mow the lawn immediately before spraying a
nicotinoid insecticide, so that flowers are not present in the lawn at the time
of application. Please note this is
approach is also in compliance with the
precautionary statements on the pesticide labels which specify not to apply
clothianidin, or other neonicotinoids, to blooming nectar-producing plants if
bees are visiting the treatment area. An
alternative may be to use chlorantraniliprole which did not appear to be as
harmful to bees in the Kentucky study.
Also, homeowners and lawn care professionals should follow three simple
steps of MSU Smart Gardening to grow turf with a dense root system that is
tolerant of grubs, so that no insecticide is needed:
1.
Mow lawns at the highest cutting-height setting on your lawn mower
2.
Use at least 2 lbs N per 1000 square feet per year
3.
Water lawns during dry periods
