Dr. Albrecht Koppenhoffer from Rutgers University and his
team of graduate students were here last Tuesday morning collecting turf and
soil samples from the Annual Bluegrass Weevil study plots on the 7th
fairway. Over one hundred samples of turf and the underlying thatch layer were
taken. Dr. Kopppenhoffer also, by request, took samples from outside the study
area which we have been treating per our program to evaluate how “clean” we
are.
If you have been following this blog, you can appreciate how
much damage this hard to control insect is. Adults lay eggs in shortly cut poa
annua turf, predominately in the fairways, tees, greens collars, and sometimes
along the outer edges of the greens. The larvae feed inside the sheath of the
turfgrass plant and after the third instar, drill out and feed on the crown, or
the growing point, of the plant. This feeding kills the plant. After feeding on
the plant, the larvae bury underneath the thatch layer in the soil and pupate
into an adult that will mature to lay eggs, repeating the cycle several times
per year. Due to the nature of the “beast”, all stages – adult, larvae, pupae –
can exist in turf at the same time. Each stage requires different control
chemistries and the weevil can easily and rapidly develop resistance to insecticides
used to control the different stages of growth. An insecticide that works one time may not work the next. The trick is not only timing the growth stage and
applying the correct pesticide, but also to change them up so that resistance
does not get out of control. Unfortunately, there are very few insecticides
that treat the Annual Bluegrass Weevil at each stage, so choices of control and
rotation are very limited. On some
courses, nothing works well enough to prevent widespread damage. Luckily, we
have not reached that point, and one of the reasons that we were chosen for
this study is because we have a population of weevils that hasn’t developed
serious resistance.
We have been pretty good with rotating chemistries and
timing applications, but we have only been treating for five years. Courses
that have been treating weevils for far longer have developed resistance, which
is no fault of the superintendent. With so few controls, resistance is bound to
happen at some point. Our goal is to try to keep it at a minimum for as long as
we can.
