Questions from the Master Gardener Hot Line: Nematodes to the Rescue!

Nature's Way to Control Beetles and Grubs

by Pat Vance

Volunteers for the Philadelphia Master Gardener Hot Line have researched and answered some interesting questions. From time to time, we'd like to share some of those with you.

Photo: Philadelphia Master Gardeners

If you have a question about gardening, call us at 215 314 8711 or send an email to philadelphiamg@psu.edu

Photo: PSU Extension

Beetle and Grub Infestation:

His pepper plants did great for several years, but during the last three years, they have suffered from beetle infestation. He begins to see grubs, the larval stage, starting in June. By the end of the month, the beetles are swarming. They devour blossoms and chew through the petioles of the leaves, leaving behind a ragged sorry-looking stem with dead leaves scattered on the ground. When the beetles disappear in another month, the plants recover. But his crop of peppers is diminishing with each season. He doesn't want to use pesticides. Is there another option?

Photo: PSU Extension

Cultural Practices: 

He can till the soil in the spring to remove the grubs, and he can rotate plant positions every year.  

Turning over the soil has advantages in a few ways, but it can also increase annual weed growth. It is also tedious and may not be completely successful for removing all the grubs.

Photo: OR State Univ Extension Master Gardener

Rotation of crops is always a good idea for many reasons. In this case, the beetles don't bother the tomatoes or leafy greens. They go straight for the peppers.

In a large garden, moving the peppers from year to year can help. However, this man has a small garden. Flying beetles won't have any trouble locating plants that are now only a few feet from last year's site.

Biological Control: 

Photo: PSU Extension

Nematodes to the rescue! Nematodes are tiny, clear worms that occur naturally in nearly every ecological niche on earth. There are thousands of kinds of nematodes found in soil, and fresh or salt water from the hottest to the coldest climates, including mountains, deserts, and deep ocean trenches. Most of them are tubular, tapered at each end, and cannot be seen with the naked eye.

 There are a few nematodes that can cause damage to plants, but the ones of particular interest to gardeners are parasitic nematodes, often simply called beneficial nematodes.

Photo: PSU Extension

Beneficial nematodes kill the larvae of many species by piercing and entering them, and then secreting toxic bacteria.

Photo: PSU Extension

The nematode divides inside the dead grub. Then the progeny move on through the soil, using differences in heat and CO2 to find more grubs. Many kinds of soil-dwelling pests can be controlled this way, including beetles such as Japanese and Green June beetles, maggots, fleas, and several kinds of weevils and borers. They are useful for infestations of grubs on lawns as well as in garden beds.

Here is a link to an article on beneficial nematodes from Penn State Extension

http://ento.psu.edu/extension/factsheets/parasitic-nematodes

Photo: Arbico

The nematodes should be applied when the grubs are growing in the soil. For many insects, that's in the spring, but be sure to identify your garden pest carefully and understand the timing of its life cycle.

A few million nematodes can be applied to a 1000 square-foot garden and successfully contain pest infestations. One application may be enough, but in some cases, the nematodes must be re-applied for a couple of years.

You can buy beneficial nematodes from a few sources. Here are links to a few:

Gardens Alive!: https://www.gardensalive.com/article1101

Buglogical: https://www.buglogical.com/beneficial-nematodes/

Arbico Organics: https://www.arbico-organics.com/category/beneficial-nematodes

Arbico has a very good FAQ page on beneficial nematodes:

https://www.arbico-organics.com/category/beneficial-nematodes-faqs

Application:

The nematodes may arrive suspended in a liquid or gel, on a sponge, or in moist granules. They are added to water, gently stirred to break apart any clumps, and allowed to soak for a short time. The exact procedure will be explained in the product insert.

Photo: City of Tillamook, OR

The slurry is then sprinkled on the garden. This can be done with anything from a watering can to commercial sprayers. They will settle to the bottom of the can or bucket, so the water should be stirred frequently during the application. They will clog fine filters and meshes, so it's best to leave those off. Remember that nematodes are living organisms and should be handled gently.

Nematodes need moisture, so the soil should be watered well before application and then lightly afterward. Late afternoon is ideal to avoid the hottest temperatures of the day until the nematodes have established themselves in the ground.

For more information, here are a couple of additional links:

UMass Amherst: https://ag.umass.edu/landscape/fact-sheets/beneficial-nematodes

UMD extension: https://extension.umd.edu/hgic/nematodes

Using parasitic nematodes is a safe, sustainable, and easy way to manage garden pests that live in the soil.

Photo: PSU Extension

If you have any other questions and are not sure where to turn, ask the Hot Line! If we don't know the answer, we know someone who does!