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Issue link: https://read.dmtmag.com/i/182361
color, which indicates that they have made all the fat that they are going to make for the season and they've stopped feeding. During this same time, the grubs in central Ohio are still very white and still feeding.Why is this important? While many insecticides have contact activity (absorbed through the exoskeletons), the primary mode of getting insecticides into the insects is by ingestion. In short, the closer you get to the transition zones, the earlier that annual white grubs may stop feeding for the summer/fall season. At present, products containing trichlorfon (Dylox) or clothianidin (Arena and Aloft) seem to have the best chance of killing large, third-instar grubs — if they are feeding. Both products tend to kill the grubs within three to five days, which will also stop any animal digging. In our field tests, the other neonicotinoids, imidacloprid (Merit) and thiamethoxam (Meridian) will kill third instar grubs, but they often take 10 to 14 days. I also commonly recommend spreading Milorganite fertilizer (made from human sewage sludge, which no longer contains any heavy metal contaminations) over the area where animals are digging, as this will chase them away for a week or so while the insecticide is doing its thing. Schroder: What are your recommendations for preventing a future reoccurrence of grubs in the same turf? Dr. Shetlar: Most of the registered grub control products (other than Duocide, which contains carbaryl and bifenthrin) can be used as preventives.This generally means to apply them before egg hatch of the annual white grubs. In most of the cool-season zones, this would be applied by mid-July. In my grub efficacy chart, imidacloprid, thiamethoxam, clothianidin (the neonics) all give 90 percent or better control if applied in June, July into mid-August. If you move into May, imidacloprid and thiamethoxam seem to run out of effective residuals. Of course, the new insecticide is chlorantraniliprole (Acelepryn) which can be applied from April through early August and get excellent grub control. Whether to treat or not can often be answered by the research that was done by Mike Villani when he was at Cornell (unfortunately he passed away while still a relatively young turfgrass entomologist). He surveyed lots of golf courses and lawns in New York over several years. He found out that if an area of turf had a damaging population of grubs, it was in the 80 percent risk level of repeating a damaging population the following year. In short, treat areas where grub damage has been previously noted. Dr. McGraw: I think that we can minimize the effects of white grub damage substantially by develop- www.landscapeirrigation.com ing a healthy turf stand. All the things you learn in Turf 101: adequate (not excessive) nutrients and water, minimize compaction, improve drainage as much as possible, and, most importantly, develop a deep and extensive root system. A healthy stand will definitely tolerate more white grubs without showing signs of damage than a stressed stand. Also, spend a day or two scouting out and mapping infestations. Take a golf course cup cutter, regularly sample (in certain grid-like patterns), break apart the core in quarters and visually assess whether grubs are present. Try to identify what species of grub it is by looking at the raster pattern (row of spines on their butts). But, most of all, keep good records. Grubs tend to appear in the same areas year after year. Find out what it is about that area that causes them to return — adult food sources, under-watered, over-watered, shaded, full sun, turf species? Schroder: Do you recommend using nematodes to combat grubs? Why or why not? Dr. McGraw: Nematodes may provide both short- and long-term suppression of white grubs, and definitely have a place in grub management.You need to become educated in their proper use and application though. These are living organisms, and need to be handled with care. There are some major hurdles in their adoption in many areas, namely their price and the product supply chain. However, as is the case in many states like New York, where we have a ban of chemical pesticides on primary school grounds and daycares, this may be one of a handful of options for controlling white grubs. I hope that their adoption is greater in the future, because it is an environmentally responsible approach. However, it is a case of economics right now. There needs to be a greater interest or demand from turf managers before the market can respond to the supply issues. Only then will the price come down. Dr. Shetlar: I only recommend the insect parasitic nematodes for organic lawn care and for homeowners who wish to use non-pesticide techniques. They are still relatively expensive to use, and you need to arrange with the supplier to ship the nematodes at the time you are going to apply them. In short, you have to use fresh nematodes. And, when you get them, they have to be applied quickly, with lots of pre-irrigation and post-irrigation. Even with the best of applications, it has been my experience that they will fail about 25 to 40 percent of the time. However, when they work, they often work very well! Bottom line, they are expensive, difficult to use, and the risk of failure is relatively high. LI Landscape and Irrigation 17