Controlling White Grubs and Japanese Beetles in the Home Garden
There are many beetles that produce white grubs, but the five most likely to damage lawns are the larvae of the Japanese beetle, oriental beetle, northern masked chafer, European chafer, and Asiatic garden beetle.
- About White Grubs / Larvae
- About Beetles / Adults
- Determining Whether or Not Treatment is Needed
- When to Treat for White Grubs
- Controlling White Grubs
- Controlling Adult Beetles
White grubs hatch in late July to early August and immediately start feeding on plant roots, with feeding activity reaching its height in October. Most grubs attack turf grass roots, although some, such as the Asiatic garden beetle, prefer the roots of perennial plants, vegetables, and flowers. Grubs burrow deeper into the soil as the weather cools and spend the winter deep underground. As the soil heats in spring, they resurface and resume eating until pupating into adult (beetle) form in June.
>> Back to Top
The adult beetles primarily eat foliage, although some will also feed on flowers. Different beetles are attracted to different types of plants but, between them all, pretty much any plant in your garden is fair game.
>> Back to Top
Scout for grubs in late summer. Dig up a one square foot piece of sod approximately every 10 feet throughout your lawn and count the number of grubs in the soil below the turf. Focus on areas where there has been grub damage in the past and/or spots that are highly visible (i.e., where you want the grass to look its best).
If there are fewer than 5 grubs per sample there’s no need for treatment. But if you see 8 or more grubs then it’s time to consider treating your lawn.
After putting back the sod, don’t forget to water well.
>> Back to Top
When to Treat for White Grubs
Any treatment should be done in late summer before damage becomes apparent (mid-July to early August). Don’t bother treating in spring – it’s a waste of pesticide and money and won’t affect the fall population of grubs and beetles.
Eggs are laid in July, hatch by mid-August, and the grubs start feeding immediately. When the grubs are small they are most susceptible to biological and chemical products. As they start feeding, they’re close to the surface where a drench with a liquid product can easily reach them.
>> Back to Top
Controlling White Grubs
Cultural Controls – The type of grass and amount of watering doesn’t substantially impact the number of white grubs in a lawn. Mowing your grass high, maintaining a healthy, vigorous lawn, and encouraging beneficial insects in your garden will help to some extent.
Biological Controls – The biological controls that are currently available have limited impact on white grubs in northern states. The soil is generally too cool for milky spore to be effective (and, when it does work, it is only effective against Japanese beetles), and parasitic nematodes have shown mixed results. If you do choose to use parasitic nematodes, buy them fresh, keep them moist, and apply them immediately in early to mid-May, preferably during a light rain or followed by irrigation.
Chemical Controls – Preventative applications of chemical controls are more environmentally friendly than are curative applications and greatly reduce the incidence of lawn damage. However, it does require the application of chemicals in anticipation of grub problems, rather than when grubs are known to be present in large quantities.
- Imidacloprid is the most effective chemical for white grub control. It is a nicotine-derived systemic insecticide belonging to a group of pesticides called neonicotinoids. Although it is non-toxic to humans and earthworms, many experts believe that imidacloprid is one of the agents responsible for colony collapse disorder in honey bees, possibly due to build-up of imidacloprid in flower nectar and pollen. So if you’re going to use it, make sure to apply it to your lawn only, avoid overspray that could hit flowers, and apply it early morning or evening when bees are less likely to be present. Imidacloprid is commonly sold as Merit (to the professional applicator only). Other trade names include Gaucho, Admire, Advantage, Confidor, Provado, and Winner. It must to watered in after application and starts working after 2 to 3 weeks. It remains active for about 3 months.
- Halofenozide, an environmentally soft pesticide known as Mach2 (Molt Accelerating Compound), forces a larva into a molt before its normal time. Currently it is only available to professional applicators.
Controlling Adult Beetles
Biological Controls – There are several options for controlling adult beetles in the home landscape.
- The fly parasite Istocheta aldrichi is a naturally occurring adult beetle parasite and when its numbers are high, can regulate beetle populations. Each female lays up to 100 eggs in 2 weeks on the thorax of female beetles. The hatched maggots bore into the adult beetles which quickly kills them.
- Trapping using yellow fin traps with trap bags below can trap up to 75% of beetles that approach them. Empty bags each day into a bucket of soapy water. Place on property lines or yard edges to attract beetles away from lawns, ornamental and garden areas. These traps can attract beetles from several neighborhood properties at one time – you don’t want to be the one house in the neighborhood with all of the beetles dining on your plants! Traps using sex pheromones or floral scent lures should only be used during the breeding period of the beetles (late June-late August).
- Hand picking in early morning is helpful. Put beetles into a bucket of soapy water.
Chemical Controls – There are numerous compounds available for Japanese beetle control. A good garden or agricultural center will provide you with many good choices. When using any of these pesticides, be careful near water and check for environmental information. Many of these chemicals will affect not only pests like Japanese beetles, but also beneficial insects like praying mantids, lacewings, and bees, so be sure you really have no other options before using chemical controls. Always follow label directions.
- Azadirachtin is a botanical insecticide and insect growth regulator from the Neem tree in India under numerous brand names including Azatin XL and Orazin 3% EC
- Rotenone is a botanical insecticide, from several plants including barbasco, nekoe, timbo, cub, and haiari.
- Pyrethrins (pyrethroids) a botanical insecticide and its synthetic derivatives cylfuthrin, bifenthrin, and deltamethrin etc., are effective. They are replacing many older pesticides on the market.
- Carbaryl (brand name Sevin). Very toxic to bees, so should be used extremely carefully, if at all.
- Imidacloprid (brands Merit, Grub-X) can be used as a systemic in perennials. Please be sure to follow the precautions listed above (see Controlling White Grubs).
Note: Mention of a product or company is for informational purposes only and does not constitute an endorsement by GPReview.