I had several reports of breakthroughs with Meridian when applied prior to mid-May. I have reviewed our efficacy data and it does appear that both imidacloprid (Merit) and Meridian are the neonics most susceptible to degradation when applied prior to mid-May. Clothianidin (Arena and Aloft) seem to be less susceptible to this. I think that this is one of the reasons that Bayer recommends using the 0.4 pound rate for the early applications. Our data suggest that applications of Meridian or imidacloprid from the last week of June though most of July should yield 90+ percent control.
With that said, I had a course in Sunbury that complained about failure of Meridian. I checked the spots out and there was considerable thatch in those areas (three spots down two fairways and the irrigated rough along one fairway) which ranged from 3/4 to 1.25-inch in thickness! Remember that none of these insecticides will reach the soil-thatch interface when you have more than 1/2-inch of thatch! The second course was also having some skunk digging. I found only about 3 to 5 grubs per square foot in that area, but noticed that there was even more digging in an untreated rough. I checked out that spot and there were nearly 40 grubs per square foot! I suspect that this course had very high grub populations and that the insecticide did pretty well, but left some grubs to survive. In this case, the skunks had obviously not read the textbooks that state that you shouldn’t have grub damage unless you are seeing populations in the 8 to 10 per square foot range!
Posted by Dr. David Shetlar, May 26, 2009 on http://buckeyeturf.osu.edu