The annual bluegrass weevil (ABW) is a growing
problem on cool-season turfgrass in the US and Canada. As one of
the more damaging insect pests on golf courses, the ABW often eludes turf
managers, finding new ways to escape control tactics and wreak havoc on high-value
playing surfaces.
The pest continues to migrate to new geographies and plague new
species' of
grass and heights of cut not previously considered to be susceptible as a
primary food source. Resistance to key insecticides, multiple generations
per season, and highly specific measures required for control make this one of
the most nuanced and costly pests to manage.
Below are some simple tips and tricks to keep in mind
when taking on this minuscule monster of turf.
Overwintering Adults
Each spring, adult weevils migrate from wooded or natural rough areas to
feed and mate – eventually moving into low-mown surfaces like fairway
perimeters, tees, collars, and sometimes greens, where
the females prefer to lay eggs. Although the timing of migration depends on weather
and microenvironments on each golf course, phenological and growing
degree day (GDD)-based models can be used to reliably predict when adult
emergence and peak densities occur.
The spring adult stage can play an important role in
the control of ABW populations around the golf course because it is the only
time of the year when a single life stage of the pest is present. A properly
timed insecticide application can go a long way in keeping populations of
future generations low for the rest of the season.
·
Plant phenology
o
Forsythia near full bloom – adult emergence
o
Forsythia half gold half green – adult
peak densities (best time to treat)
·
GDD [base temp 50 F]
o
25 - 75: Adult emergence (can vary greatly)
o
125 - 175: Adult peak densities
Commonly used insecticides against adult ABW are synthetic
pyrethroids (Scimitar,
Talstar)
and combination products (Aloft, Alucion, Triple
Crown). The effective adulticide chemistries tend to have a very short
residual activity, so timing an application against peak adult densities is
critical. Management decisions against adult ABW populations need to be based
on a multitude of factors including population density, damage
thresholds, and insecticide resistance to name a few.
Early-Season Larvae
The spring ABW larvae hatch from their eggs and begin to develop inside the stems
of the turfgrass plant. A sheltered development along with its small size makes
the ABW a very difficult pest to diagnose and manage once present on a golf
course. As the larvae mature, they go through several molting stages
(L1-L5) which play an important role when choosing a control strategy.
The process from egg lay, to pupation, to the next
generation of adult emergence, takes roughly 30-40 days. While physical
scouting and sampling are the best way to determine the life stage on any given
property, management decisions aimed at targeting ABW larvae can also be guided
by GDD and phenological indicators.
·
Plant phenology
o
Full bloom flowering dogwood - adult eggs
laid (adulticides likely not effective)
o
Peak bloom Catawba rhododendron - 3rd
- 4th instar larvae transitioning to outside of the plant
·
GDD [base temp 50 F]
o
~175 GDD - egg lay has occurred (adulticides likely
not effective)
o
~350 GDD - 3rd - 4th
instar larvae transitioning to outside of the plant
There are several classes of chemistry available that can
effectively control ABW larvae either by contact or ingestion as the
insect feeds on the plant tissues. These include the anthranilic diamides
(Acelepryn,
Ference,
Tetrino),
spinosyn (Matchpoint),
neonicotinoids (Arena,
Merit),
and other broad-spectrum contact insecticides like Dylox
and Provaunt.
The timing and placement of these applications can be critical to their
success.
Summer/Asynchronous Generations
Surviving larvae from the spring generation pupate to emerge as “general”
adults and begin the mating and egg-laying process all over again. Recent
research has shown that female ABW adults can lay eggs over 14 weeks,
which creates issues of “asynchronous” life stages across the golf
course.
Managing ABW later in the summer months is more difficult
due to the variability in the life stage found at any given point. Should you
apply an adulticide? Early larvicide? Late larvicide? All of the above? The
answer is often unclear, which is why gaining the upper hand on populations in
the early part of the year is so important.
At this point, most options are on the table, but scouting
will be increasingly important to understand where the issues are occurring
around the golf course and the predominant life stage(s) of the population to
make the best management decision.
Below are Some Key Considerations in Product Selection at Any Stage of Your ABW Program:
·
Resistance management - rotating
chemistries and active ingredient classes to reduce selection pressure
on the population. Resistance to synthetic pyrethroids is common and widely
documented.
·
Environmental stewardship - many
insecticides can have non-target or unintended consequences on beneficial insects
or other organisms. Consider products that have improved environmental
profiles and less restrictive use patterns where possible.
·
Other pests of concern - To get the most
“bang for your buck” select products that not only achieve optimal control of
your ABW population but may also aid in the control of other key pests of
concern like white grubs, chinch bugs, caterpillars, etc.
There are some excellent resources from university
entomologists and extension personnel to tap into. If you haven’t already, sign
up and follow the Syngenta
WeevilTrak site for local updates and alerts on ABW life stages and
progress throughout the season. Other resources of note are below:
·
https://www.greencastonline.com/weeviltrak/display.aspx?tmname=treating-for-abw
Reach Out to Your Harrell’s Rep for More on ABW
If you have any other questions, concerns, or are looking for more information on ABW/prevention, reach out to your local Harrell's rep.
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