Pest type: Insects
Grubs, or more specifically white grubs, are the larvae of scarab beetles, Japanese beetles, June beetles, chafers, and others. They are one of the nation’s most destructive lawn pests. These organisms are C-shaped, off-white in color with a characteristic dark brown head. The larvae feed on grass, plant roots and organic matter in the soil. As a result, grubs can be found at the root zones of damaged areas of the lawn. It is important to identify grubs as the source of your browning lawn before utilizing biological treatments highlighted below after trying preventative methods. Other factors, such as drought, disease, excessive fertilizer, poor soil or even another pest, may be the cause of your lawn’s brown spot.
Check the mowing height of your lawn mower. Adult beetles prefer to lay their eggs in short grass. Cutting your grass tall – minimum of 2 inches high – may discourage egg laying, and reduce future grub populations.
Aerate your lawn. Cultivate a healthy lawn by encouraging deep grass roots. Deep roots have a greater chance of surviving a grub infestation. Grubs that may be feeding on roots deeper into the soil are spread out over a larger area, making their damage less discernable. Aerate your soil, either by hand or aerating equipment, in the spring and fall to promote deeper roots.
Consider your watering frequency. Lawns that are heavily managed and watered regularly, especially during the summer months, may actually attract beetles. Eggs require moist soil conditions in order to hatch and prevent the larvae from drying out. Therefore, deep periodic soaking of the turf is more beneficial than frequent, light watering. Infrequent watering also encourages roots to grow deeper into the soil. If there is moderate grub infestation, watering in late August or September, can promote tolerance and recovery.
Be sure to continuously monitor your lawn every year, sampling in early to mid August, at the start of the grub’s life cycle. For an otherwise healthy lawn, a couple grubs per square foot (0-5 grubs per sq ft) is not considered to be a problem. If there are 6-9 grubs per sq ft, you may want to take into consideration the overall health of your lawn. If your lawn is healthy, has a robust root system and is dense, it can probably withstand a few grubs. Otherwise, you may want to consider treating your lawn. For more than 10 grubs per sq ft, treatment should be carried out.
Mechanical traps that lure adult beetles (with food type lures or pheromones) can be placed around the borders of your property and can capture around 75 percent of beetles that approach it. Setting up traps should coincide with the emergence of beetles in your area. Since these traps attract more beetles than they can catch, it is advised that traps be placed away from plants susceptible to beetle damage. However, do not use traps if you currently do not have beetles visiting your property! Traps can be obtained from many garden centers.
Few least-toxic chemical options are effective at grub management, see above for cultural, mechanical, and biological controls for grubs.
Look at your product labels and try to avoid products containing those chemicals listed below:
(A = acute health effects, C = chronic health effects, SW = surface water contaminant, GW = ground water contaminant, W = wildlife poison, B = bee poison, LT = long-range transport)