Q. How do I naturally eliminate grubs in my lawn?
Severe grub damage in a lawn appears as large, irregular sections of brown turf. Unlike a lawn damaged by drought or excessive fertilizer, grub-damaged turf peels away like a carpet because most of the roots are gone. Due to the grubs' life cycle, damage appears in late summer and early fall, when grubs are large and feeding near the surface. The open spaces created by these pests can be ugly, vulnerable to erosion, and invaded by weeds.
Grubs can cause considerable damage because they feed on root hairs, preventing plants from taking up adequate moisture. They are the larval stage of scarab beetles (such as Japanese beetles, Oriental beetles and European chafers). Because these beetles differ in life cycle and behavior, the treatment you choose should correspond to the species of grub in your lawn or garden. You can have your grubs identified at a local Cornell Cooperative Extension (CCE) office, or consult a guide such as U. Mass Amherst's. (Grubs are identified by differences between the "raster patterns" on the tail end of the grub.)
When treating for grubs, lawn health makes a difference. Vigorous, healthy turf will not show as much grub damage as thin, over-fertilized turf. Raising the mowing height to 3 1/2 to 4 inches will promote a deeper, more extensive grass root system. To alleviate compaction and increase the soil's organic matter content, core aerate the soil and apply composted cow manure from around Labor Day to early fall. Also, check the pH to be sure that levels do not fall below 6.0. or rise above 7.0. At low and high pH ranges, nutrient levels become less conducive to turf health. High-nitrogen fertilizer in spring is detrimental because it promotes shoot development without a good root system. Very damaged turf should be re-seeded with an improved seed type.
Evaluating the concentration of grubs in your soil can help you decide whether or not you need to treat these pests. Peel back a square foot of turf, count the number of c-shaped white grubs, and then replace the grass. Usually, a count of 8 or more grubs per square foot means you should take action.
Options for treating grubs include beneficial nematodes, imidacloprid (Merit), or trichlorfon (Dylox)--listed from least to most toxic. In some areas, imidacloprid may only be used if applied by a certified pesticide applicator. Clothianidin (Arena) and thiamethoxam (Meridian) may also be available; check with your local cooperative extension office. Sample and treat when grubs are young and actively feeding close to the soil surface – mid-August to late September in upstate New York, early August to mid-September in the southeastern part of the state. If your lawn had a serious grub problem the previous year, preventive chemical treatment in spring or early summer may also be an option.
There are also many natural enemies of white grubs already in your soil, including ants and ground beetles. To preserve these natural predators, use spot treatments instead of blanket insecticide applications.
For detailed information on grub treatment and control options, see Cornell University's guidelines.
For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service