Beneficial Iris Nematodes: Using Nematodes For Iris Borer Infestations

Beneficial Iris Nematodes: Using Nematodes For Iris Borer Infestations

By: Tonya Barnett, (Author of FRESHCUTKY)

Due to their wide adaptability, irisesare a popular choice for many home gardeners. These plants range in size fromdwarf to tall, and come in a wide variety of lovely colors. Due to theirperennial nature, irises can easily find their place in already establishedflower borders and landscapes or in new plantings. Though novice gardeners areable to grow these flowering plants quite easily, there are some issues whichmay cause a decline in iris plant health. Most commonly, iris borerscan damage and even destroy iris plantings. With the addition of iris borernematodes, however, this may not become an issue.

How are Nematodes Good for Iris?

One of the most common nuisance pests of iris flowers is theiris borer. In the fall, borer moths lay eggs on the soil near iris beds and onold plant matter in the garden. The following spring the eggs hatch and thelarvae burrows into young leaves. As the borers feed, they gradually worktowards the rhizome of the iris. Once in the rhizome, borers continue to causedamage until they mature.

This damage can cause severely stunted plants or even thetotal loss of iris rhizomes. In the past, iris borers have been extremelydifficult to control through various chemical applications. Recently, the useof beneficial nematodes for iris borers has been brought into focus.

Microscopic nematodes for irises live in the soil. Theseentomopathogenic nematodes are able to find and feed on iris borers and theirpupae, thus preventing damage to iris plants. However, when using nematodes foriris borers, timing will be most important.

Using Beneficial Iris Nematodes

After hatching early in the season, iris borers will be presentin the soil as they search for young iris leaves in which to infect. This isthe ideal time for nematodes to be released. Just as with any other productused in the garden, it will be vitally important to follow the manufacturer’slabel carefully. If used incorrectly, the beneficial iris nematodes may havelittle to no impact on the borers.

In addition to applying iris borer nematodes in spring, manygrowers also choose to apply them in the fall. The use of a fall applicationcan help to destroy any remaining adult larvae or pupae that is left in thesoil. By doing so, this can greatly reduce the number of adult moths whichoccur in the garden the following growing season.

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Thousands of NematodesLaunch An Iris Borer Attack

Ten million worms can be a good thing!

Nematodes are a microscopic round worm, many species of which are parasitic on insects. Steinernema carpocapsae is a species that attacks the larval form of several ugly plant killers. My interest is in their ability to attack the dreaded Iris Borer.

This enemy of my favourite flower, overwinters as eggs on plant debris and then hatches and migrates across the soil until it finds a juicy Iris plant and then it moves in and starts to hollow it out. If the Nematodes are wandering around the garden during this migration then they will find the little borers, infest and kill them. There are a few suppliers of these creatures in the U.S. but now there is one in Canada that makes my life easier. They have sent me a few million of these little worms to try and they have been applied to the soil as per instructions. I will continue to update this page as I chart the success of these beasties in eliminating my resident Iris Borers.

When Do I Do This? I applied them in late May when the Iris where well developed and I’m worried that it might be too late. The borer’s eggs should have hatched and migrated to my Iris already and I don’t know about the efficacy of these little parasites once the borer is comfortably ensconced inside the Iris leaves. They may be able to find the large older larva that hollows out the rhizome but by then a considerable amount of damage has already been done to the Iris plants. We will wait and watch carefully. They need to have a soil temperature of 50 F to become active so cannot be applied too early.

How Do They Get Here? They arrived on a sponge. A relatively small sponge considering the number of little worms that were supposed to be present. The sponge was dropped into a gallon of water and the little creatures migrated into the water to make a stock solution. The directions said they would cover 2000 sq ft and that works out to 20 sq ft for each of my 100 Iris plants. Seems to be more than enough. I filled a watering can with water and soaked around a few Iris clumps to see how many I could do with one can of water. Four seemed to be a good number. Therefore I needed 25 watering cans full of Nematodes to cover all of my Iris. A little quick math told me how many ounces of stock solution was needed in each watering can of water and away we went mixing and sloshing and distributing nematodes around the entire garden. As they are microscopic, we can only assume that each Iris now has a reasonable population surrounding it and we will wait and see what happens.

What Else Will They Kill? This company, Natural Insect Control, also sells a box with a mixture of two different nematodes in it, that should be an effective and totally pesticide free method of controlling the white grubs in your lawn. As those grubs spend at least a year and often two as larva in the soil, the timing of the application should be much less critical. My small turf areas are not my garden’s best feature so I really don’t have a grub problem and therefore can’t accurately assess the effectiveness of this control. I do know that people whose opinions I trust say that it really does work.

Huge disclaimer here. I didn’t actually do any of this. The Nematodes arrived at my garden when I was away playing Grandpa to my twin grandchildren and the "Assistant Gardener," my long suffering wife, was left to communicate with me by phone and then go out and do all of the steps that I have described above. Luckily she has an affinity for Iris as well. My local garden center sells this product and it is available from the company website. $30 to protect all of my Iris or to rid your lawn of grubs with no pesticides seems a pretty good deal.

Did It Work?
Yes! The vast majority of my Iris grew better then they have for several years. 2 or 3 varieties were still attacked by the Borer. Whether they were missed during the nematode application or whether they are just very susceptible varieties, I really don't know at this point. As I had to dig them out anyway to get rid of the mess and to look for borer pupa, I only replanted one of the attacked varieties. We'll see how it fares next year.

Biological control with beneficial nematodes

Beneficial entomopathogenic Steinernema carpocapsae nematodes (Photo 3) can be used to control only mature larvae and pupae of iris borers to stop their future generations. This is because all the young stages of iris borers feed internally on the leaf and rhizome tissues and therefore cannot be easily treated with beneficial nematodes as opposed to mature larvae and pupae that are present in the soil and can be easily treated with Steinernema carpocapsae nematodes.

Photo 3. Beneficial entomopathogenic Steinernema carpocapsae nematodes

For the effective control of iris borers, apply 25,000 Steinernema carpocapsae nematodes around iris plants in your flower garden using a watering can with a sprinkler head (Photo 4). Apply nematodes early in the morning or late in the evening so that they will not be exposed to UV light as it kills them instantly. Since nematodes need a film of water for their movement in the soil, immediately irrigate all the nematode treated area.

Garden Army Multi-Purpose Nematodes

Controls vegetable & small-fruit insect pests

  • Steinernema feltiae
  • All-natural control for a wide variety of pests including fire ants
  • Environmentally friendly, non-chemical beneficial microscopic worms
  • Best to apply in the spring/fall

Begins shipping late February

There are hundreds of grub types waiting to do their damage to lawns, fruits, veggies and ornamentals. There are also specific nematodes that are helpful for targeting certain pests. But what if you're not sure what type of pest you have? Or maybe you're dealing with several pests. In cases like this, it's best to rely on Garden Army Nematodes. They control a broad range of common garden pests and are even a great solution for getting rid of fire ants!

What are Nematodes? Nematodes are microscopic, beneficial predatory worms that hunt down and kill pest insects but pose no threat to people, pets or plants. They won't harm beneficial insects, either. They're an environmentally friendly, non-chemical solution to get rid of grubs and many other soil-dwelling pests.

Application Rates. 5 million nematodes will cover 200 sq. ft 10 million nematodes will cover 400 sq. ft. Reduce coverage area by half for heavy infestations. Only infested areas need to be spot treated, and it's a good idea to extend treatment a couple of feet beyond the infested area. There is no need to treat non-infested areas as grubs tend to return to the same area year after year.

Pests Controlled. There are a variety of beneficial nematodes, and while more than one type can control several of the same pest insects, some nematode varieties are better suited for controlling certain pests. Garden Army Nematodes are effective at controlling a very broad spectrum of soil-dwelling pests including: Armyworms, Banana Root Borers, Black Currant Borers, Black Vine Weevils, Cabbage Root Maggots, Carpenterworms, Codling Moth Larvae, Corn Earworms, Corn Rootworms, Crane Fly Larvae, Cucumber Beetle Larvae, Cutworms, Dogwood Borers, Fire Ants, Flea Beetle Larvae, Flea Larvae/Pupae, Fungus Gnat Larvae, Gypsy Moth Larvae, Iris Borers, Japanese Beetle Larvae, Mole Crickets, Onion Maggots, Peach Tree Borers, Pine Weevils, Poplar Clearwing Borers, Raspberry Crown Borers, Root Knot Nematodes, Shore Flies, Sod Webworms, Strawberry Weevils, Sweet Potato Weevils, Thrips, Tobacco Budworms, White Grubs and Wireworms. (Garden Army Nematodes are best suited for pests in bold.)

Effectiveness. Garden Army Nematodes can be applied anytime the soil is not frozen, but become active at soil temperatures of 55°F or above. Nematodes are most effective at controlling grubs in the spring and fall. Once they're applied, look for the adult pest population to begin dwindling in 1-2 weeks. Garden Army Nematodes kill pests at the larval and pupal stages, so they'll prevent future pest populations once the adults die off.

Nematodes are packaged with diatomaceous earth (which is mostly silica), water, and potassium sorbate.

The Silver Lining

Although I’d like to rid my bearded iris plants of borers to keep the plants looking and performing their best, it’s important to note that an iris borer infestation seldom kills an established iris plant. Even if a handful of the rhizomes are damaged, the rest will go on to produce healthy flowers the following year. Except in extreme cases, iris borers don’t mean the end of the road for your bearded iris plants. Gardeners like myself just need to put in a little effort to keep them in check.

Watch the video: What are Beneficial Nematodes?