Biological Control: Using Worms to Control Grubs

Published: April 20, 2015

Nematodes are unnoticed, microscopic roundworms that dominate our living world. While minute, their overall numbers are not. Four out of every five animals on Earth is a nematode, making them by far the most abundant animal on this planet. As nematologist Nathan Cobb explained in 1915, if all the matter on Earth was removed except nematodes, the planet’s outline of mountains, trees, and seas would still be dimly recognizable as ghosts represented by the remaining thin film of nematodes.

The variety of nematodes, their life habits, and interactions with other organisms is fascinating and complex. Nematodes need water, so most live in the soil, thin water films on plants, or within their hosts. Nematodes may feed on dead organic matter and detritus, or living organisms such as bacteria, fungi, plants, or other nematodes. Some nematodes have also evolved famously, and often disturbingly, as animal parasites. The animal wrapped around the stake in the medical sign that most think is a snake, may in fact be a nematode. Dracunculus medinensis is ingested in drinking water by humans and causes a painful blister infection from a female that may grow up to 4 feet long. The historical treatment was to slit open the affected area and slowly wrap the nematode around a small stick to pull out of the wound without breaking.

Some specific groups of nematode species may also be beneficial, acting as parasites of lawn and insect pests. For example, the annual white grub complex, including larvae from masked chafers, Japanese beetles, and other scarab species, is considered the most important insect pest on home lawns and other turfgrass areas in the state. The life histories of each species may differ, but generally they overwinter as grubs in the soil, and pupate in May to adult beetles. These adults, particularly Japanese beetles, feed voraciously on row crops or desirable ornamentals, and lay eggs in the soil. The new generation of grubs that emerge in late June through early August usually cause the greatest feeding damage on turfgrass roots. Another common and unwanted sign of a large grub infestation is predators such as skunks, raccoons, or armadillos, which will rip up large sections of turf for the easy and plentiful meal.

Soil-applied insecticides are often utilized in early to mid summer for control of an established grub problem. For those wanting another option, however, entomopathogenic nematodes may provide grub control if applied and handled correctly. Two genera, Steinernema and Heterorhabditis, are voracious parasites of annual white grubs and other specific insect pests. Commercially available products (Grub-Away™ & others) contain Heterorhabditis bacteriophora, which can swim through soil water films and actively hunt for its grub host. As a side benefit, H. bacteriophora will also infect and kill flea larvae, but will not impact other surface dwelling beneficial insects, you, or the dog.

Outlined below are several key factors that are crucial to effectively using nematodes for grub control in home lawns. It’s necessary to realize that a living organism is being applied. Therefore, the cost may be higher, and control will not be immediate after application. Proper handling and application is also critical, and the environment must be made suitable for the nematode.

• Grubs must be present in the turfgrass area to be treated. Infective juvenile nematodes will need a food source rapidly after application; meaning curative applications with a known grub infestation are necessary. Spot treatments of affected areas are best. For more information on diagnosis of turfgrass problems, go to http://plantclinic.missouri.edu/submission.htm.
• Order the nematodes when you need them, and apply all of them immediately after receipt. This will lessen the chance of any attrition and loss of infective nematodes during storage.
• Nematodes need water. Water the area thoroughly before application. Apply the nematodes in water (sprayer, watering can, etc) and then water them in (at least 0.25”) after application. Water daily for the next three days after application, and don’t let the soil dry out. Applying in the rain is also a good idea. Yes, your neighbors will look at you strangely.
• Apply during warm temperatures (68-86°F). Exposure to UV and heat may kill nematodes, so do not apply during the heat of the day. Early morning and late evening are the best times to apply.