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Organic Control of White Grubs in Your Lawn
There are a multitude of beetles that produce white grubs in our lawns and unless you’re an interested biologist, you really don’t care which one of the larvae are eating your grass. You simply want them to stop, die, and/or preferably go somewhere else. How do you know you have a problem? A: The grass can be easily pulled from the soil because of the large numbers of severed roots. And there are large irregular patches of yellow – dead or dying- turf. You see, the white grubs eat grass roots, reducing the ability of the grass plant to survive. Where there is enough damage, the grass turns yellow. When more damage is done, the grass withers and dies. This damage is usually in irregularly shaped patches. How do I tell damage from white grubs from dog damage? A: Dog damage leaves yellowing grass in small patches but the edges of the dog damaged areas will be growing strongly because of the fertilizer effect of the urine. The edges of the grub damaged areas will not be growing strongly. Dog damage creates multiple small patches, while grub damage tends to be larger patches. How do I know whether to treat for white grubs or not? A really interesting research project at Cornell University investigated 300 lawns in upstate New York for lawn grubs. This research found that even in a bad year for grubs, only 18% of the surveyed lawns actually passed the threshold for lawn grubs requiring treatment. The vast majority (82%) did not require any treatment at all. Any treatment would have been a waste of time and money. This is why threshold testing is so important – know what you’re trying to kill before you actually go out and waste your time and money on sprays.
So what is a threshold test? A: Peel back a square foot of the lawn sod. If you can count more than 5 to 7 beetles in this space, control. If no 5 to 7 grubs, then ignore the problem. Do this in several spots around the lawn (particularly in heavily damaged areas) and average the counts. If the average grub population is over 5 to 7 per square foot, then control. If you don’t want to bother counting, then simply apply predator nematodes every two years. I’ve heard that these predator nematodes don’t work A: You heard wrong. Sure, if you don’t apply them properly, they don’t work. These are living organisms and have to be treated as such. The real trick is to apply them at the right time for your area when the ground is warm enough and water them into the ground properly so they can swim down to feed on the grubs. Mind you, if you apply chemicals at the wrong time or don’t water them in, they don’t work either. So what’s the difference other than the predator nematodes won’t hurt you, your children or your pets. Is the grub problem the same in the South as the North? A: Well, both have white grubs. The major grub pests in the South are the June Beetle and the Southern Masked Chafer. Warm season grasses such as Bermudagrass, Zoysiagrass, St.Augustinegrass, and Buffalograss are readily attacked by the grubs. In the South, the cool season grasses such as Kentucky bluegrass are usually attacked by another June Beetle called the May Beetle. It is called the May beetle because it gets off to a faster start (in May obviously) than its cousin, the northern June beetle. While in Northern climates June beetles normally require several years to complete their life cycle. In the South, they can complete their normal cycle in one year or at most two years. Most of the damage from grubs occurs in the mid-summer to late fall period when the larger grubs are actively feeding. The best time to control white grubs in the South depends on your location. Northern lawns are heavily weather dependent and the temperatures and rainfall the grubs need to start feeding are usually quite predictable, Southern temperatures, rainfall and insect responses are not as dependable. Control is best achieved five to six weeks after the June beetles have started flying in your area (North or South). So, when you hear them thwacking off the screens, wait five to six weeks to control them. (you control them by killing the larvae, not the adults) What about Japanese Beetles? A: You can read about Japanese beetles and their control here. For the record, the white grubs you see could be one of: Is there another way to control grubs? If you want to use a totally organic approach to your lawn grub problem and get some exercise at the same time, use lawn spikes. Research studies have shown that by wearing these spiked sandals while you are mowing your lawn, you can reduce grub populations by as much as 50%. As you walk, you spear the grubs. The more you walk, the more grubs you kill. Click here for free newsletter or to ask a question about white grubs
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