Friday, June 5, 2015
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.