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GWAA

The Garden Writers Association


Last Update 08/29/12
Beneficial Nematodes

 Heterorhabditis bacteriophora and Steinernema feltiae

Beneficial Garden Roundworms

Microscopic view of Beneficial Nematodes (click image to enlarge)
Microscopic view of Beneficial Nematodes (click image to enlarge)

Not all nematodes or roundworms are harmful to human activities, actually two species in particular are very beneficial in the Florida garden. The word nematode is made up of two Greek words: Nema which means "thread" and ode which means "like". This word describes the shape of these microscopic worms which are "thread-like".

Nematodes are entomopathogenic, which comes from the Greek words entomon, meaning "insect" and pathogenic, meaning "that which causes suffering". Entomopathogenic nematodes are worms "which cause suffering" to insects and do not harm humans, pets or other animals.

 

How Beneficial Nematodes do their Job

Juvenile nematodes hunt and infect host insects. After entering an insect host through its mouth, anus or breathing holes (spiracles) -- Heterorhabditid nematodes can also pierce through an insect' s body wall -- the juvenile nematodes release a bacteria of the genus Xenorhabdus (steinerernematides) or Photorhabdus (heterorhabditids) which kill the host insect in 24 to 48 hours by liquefying its insides.

There is a symbiotic relationship between the nematodes and bacteria -- nematodes provide shelter and transportation for the bacteria which kill the insect host and provide nutrients to the nematodes. Together, the nematodes and bacteria feed on the liquefied host and reproduce inside the the dead insect's body. When nutrition stores inside the host insect begin to run out, the adult nematodes produce new infective juveniles adapted to withstand environmental conditions outside the host insect.

After about a week, hundreds of thousands of infective juveniles emerge from the hollow carcass of  the host insect and search for new hosts carrying with them an inoculation of bacteria that starts the lifecycle of the nematodes and bacteria over again.


Live nematodes from ARBICO Organics filmed under a microscope. To give a rough idea of how small these worms are (you cannot see them with the naked eye), they are wiggling around in a drop of water -- I filmed only a tiny portion of that drop.

Heterorhabditis bacteriophora nematodes roam deeply through the soil searching for potential insect hosts while Steinernema feltiae are more sedentary and wait for host insects to approach them. Some Steinernema hunt by raising up off the soil surface to attach to passing insects. Others are able to jump on passing hosts by forming a loop with their body that propels them through the air allowing them to attack their host insects.

What Insects do Nematodes Control?

Steinernema feltiae nematodes are known to control:

Fleas, caterpillars, cutworms, sod webworms, worker/soldier ants, worker/soldier termites, American cockroach, armyworm, artichoke plume moth, Asian cockroach, beet armyworm, black cutworm, bluegrass weevil, codling moth, corn earworm, cotton bollworm, cucumber beetle, fall armyworm, fly larvae, fruit fly, German cockroach, leaf miners, mole crickets, tobacco budworm, wireworm, and others.

Heterorhabditis bacteriophora nematodes are known to control:

Grubs, root zone weevils, citrus weevils, black vine weevils, queen ants/termites, Asparagus beetle, bagworm, banana weevil, banana moth, bill bug, black vine weevil, cabbage root maggots, carrot weevil, citrus weevil, Colorado potato beetle, cucumber beetle, European chafer, adult flea, flea beetle, gall midge, Japanese beetle, masked chaffer, May/June beetles, strawberry root weevil, sugarcane stalk borer, sweet potato weevil, various tree and vine borers, and others.

 

How Are Beneficial Nematodes Applied?

Nematodes are shipped in a finely ground moist clay powder that is added to water. This nematode solution is applied using a watering can, hose end sprayer, backpack or pump sprayer or through irrigation or misting systems. The best times to apply the nematode solution is early in the morning or before dusk when the temperatures are cooler and the sun is not as bright. The soil where the solution is to be applied should be moist at the time of application and lightly watered immediately after application. After application, regular watering of the treated area will provide sufficient moisture. Generally speaking, water every 3-4 days if rainfall does not occur. It is not beneficial to spray the nematode solution on plants as these round worms are soil dwellers.

Nematodes are recommended for use whenever larvae or grubs of insects targeted for control are present during the spring and fall months. Because larvae feed on plant roots, beneath the soil surface, severe damage can be done before realizing there is a problem. Look for signs of an adult insect, such as leaf-notching. If adult insects are present, their eggs will be hatching soon. Keep in mind, one application of nematodes may not eradicate a population of insects that has become established over a period of years.

Beneficial nematodes can be stored in a refrigerator for up to two months. The best way to store unused portions is to place them in a large shallow storage container and cover with about inch of water. This is to ensure that they do not dry out and that the maximum area is exposed to the air so they can breathe.

It is best to make at least two nematode applications separated by 7-10 days in order to stagger the life cycles of the nematodes and to assure complete coverage. In cases of severe insect infestations, applications should be made every 7-10 days or until infestations subside.

 

Sources: Nematode - Wikipedia, the free encyclopedia, ARBICO Organics, IPM-UCONN-Beneficial Nematodes

 
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