White grub damage in a residential lawn. Photo: N. Bosold, Penn State (retired)
How can these underground marauders be dealt with? The first thing to do is follow sound cultural practices to maintain turf health. This includes, but is not limited to:
- avoiding over fertilization
- mowing at the proper height
- core aerification at least every two years
- irrigating only when necessary
One option is to minimize the amount of turf on the property. Consider recommending your client take some areas of lawn and convert it into a plant garden of some form--maybe native plants, a pollinator garden, or even a vegetable garden. These add more color and variety to a landscape, while also removing the larval food source--the turf roots. Another option is to replace Kentucky bluegrass or perennial ryegrass (if these are the predominant species) with either a turf-type tall fescue or one of the fine-leaf fescue species. The fescues have a more robust root system and can tolerate more feeding damage before turning brown or dying.
There are two commercially available biological organisms that can be used to manage white grubs feeding on turfgrass roots. Milky spore (Paenibacillus popilliae) is a commercially available bacterial spore that must be ingested by the grub. Before using this product, there are some things you should consider. If the spores are viable, they only work on Japanese beetle grubs. Your lawn may have a mix of grub species. Also, cooler soil temperatures in the fall (comparing Pennsylvania to states to the south) lead to less grub activity and less spore ingestion.
The other biological option is beneficial (entomopathogenic) nematodes. These are microscopic, unsegmented worms. The species that can be purchased are ones that attack and parasitize insect larvae, such as white grub species. One of the most effective species for white grubs is Heterorhabditis bacteriophora. Use of nematodes requires adequate soil moisture and avoiding application during peak sun (UV light) hours. The sensitivity to UV light is one of the primary reasons that nematode use has not become more common in the landscape - turfgrass profession. It is extremely challenging to have applicators out at dusk making applications.
Your last option for dealing with white grubs is insecticides. There are few choices in this category.
- An older active ingredient is trichlorfon. This insecticide active ingredient is used as a curative and is most effective used in late August or early September when the grubs are smallest.
- Another insecticide that has been around for a while is imidacloprid. It is sold under a number of trade names. This is a preventative material that is applied to the lawn in late June to early August. Note: Imidacloprid is in the chemical class called the "neonicitinoids" and has come under recent scrutiny due to its negative impact on pollinators.
- The last active ingredient is chlorantraniliprole. This is another preventative and should go out in May or June.
Adult Beetle Management
Even though long-term management of a scarab beetle population should focus on the larval stage, the adults can also demand attention because they feed on the foliage and flowers of garden plants. The key is to protect plants early before the beetles, particularly Japanese beetle, cause noticeable damage. When the beetles feed, volatile chemicals are released from the damaged foliage. Feeding beetles also release an aggregation pheromone. Both attract more beetles, which leads to increased damage to that plant. When possible and practical, beetles can be hand removed and placed into soapy water. (This is something that can be recommended to the property owner.)
Japanese beetle damage on linden. Photo: T. Abbey, Penn State
The commercial traps that are available lure Japanese beetle adults using a sex pheromone. I do not view the traps as a management tool for reducing the population. If placed away from valuable ornamental plants, and not set in the middle of the yard, they may provide some adult feeding damage protection. However, they do not impact the overall population. Communicate clearly with your clients who put them out that they should not rely on them to eliminate the population.
- Products with the active ingredient azadirachtin (extracted from the neem tree) can act as a foliar feeding deterrent for a few days, but the product would need to be reapplied to provide any benefit.
- Contact insecticides for feeding adult scarab beetles include the synthetic pyrethroids (bifenthrin, permethrin, others) and carbaryl. Note: These insecticides are non-selective, which means they kill other organisms, not just the targeted beetles. They are also highly toxic to bees. Do not apply to plants that are flowering.
- The systemic insecticides imidaloprid and chlorantraniliprole can be foliar applied, but precautions must be taken to avoid plants in bloom.
Remember to always read the label.