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Nematodes: Overview

What are Nematodes?

You might not be able to see them, but nematodes can drastically hurt corn yields. Plant-parasitic nematodes are probably the least understood of all the pests that attack corn. Unlike insects and weeds that are easily identified, these invisible below-ground pests often go undetected. What’s more, when symptoms of nematode populations begin to appear, they're sometimes improperly diagnosed and often attributed to other problems.

Nematodes feed directly on the corn root, increase the probability of seedling diseases and can cause major losses in yield. Understanding how to manage this pest is critical to the success of the crop.

Read on to learn more about corn nematodes, and how Avicta® Complete Corn with Vibrance® seed treatment from Syngenta can help control these damaging pests and increase yield potential.

Nematodes are microscopic, threadlike roundworms that inhabit the soil and feed on root systems of crops. More than 20,000 species are known, and 4,000 of these are plant parasitic. The plant parasitic nematodes are usually less than a millimeter long and translucent, and therefore often invisible to the naked eye. All plant parasitic nematodes are obligate parasites, organisms that require a susceptible host on which to feed and complete their life cycle.

Lesion nematode
Nematodes: Overview

Where Are Common Corn-Parasitic Nematode Species?

There are many species of plant-parasitic nematodes that feed on corn. Remember that a number of factors can affect the species prevalent in your area including region, field history, climate, soil type and crop rotation, as well as cultural and management practices. The only way to make sure nematodes are properly identified is through soil sampling, which we will cover later.

Most of the major species are found nearly everywhere corn is grown but there are some regional differences in some species. It is widely held that corn nematodes are native to the United States, probably having fed on native grasses before corn was cultivated.

Problem Nematodes of the Midwest

Although some species of corn nematode can be found virtually all across the country, producers in the Midwest commonly have one or more of the following species to deal with:

  • Dagger
  • Lance
  • Lesion
  • Needle
  • Spiral
  • Sting
  • Stunt

Problem Nematodes of the South

The following commonly occur in the Southeast and deep South corn-producing regions:

  • Root-knot
  • Stubby-root
  • Lesion
  • Sting
  • Lance
  • Dagger
A lesion nematode in a corn root tip.
A gall formation caused by root-knot nematode juveniles
Nematodes: Overview

They're Everywhere!

Corn nematodes occur in every soil type, not just sandy soils. Changing production practices such as the increase in corn-on-corn production and no-till farming are helping fuel the increase in corn nematode populations, because these pests thrive in undisturbed soil.

In the past, soil-applied organophosphate and carbamate insecticides have provided some suppression of nematodes, minimizing nematode populations to the point that damage went unnoticed when these materials were used for corn rootworm and secondary insect protection. However, the switch to pyrethroid insecticides and the introduction of CRW-traited corn has left the door open for nematodes to thrive.

Nematode risk levels in the Midwest
Nematode risk levels in the South
Nematodes: Damage

What damage do nematodes cause?

Make no mistake, nematodes can and do cause serious damage to corn. In most states with substantial corn acreage, conservative estimates have yield losses due to nematodes well into the tens of millions of dollars each crop year. Regrettably, many farmers don’t know it. These microscopic pests can cause considerable damage during critical early corn growth stages, and can be difficult to diagnose because there may be no visual symptoms.

Nematodes cause significant damage to vulnerable crops by feeding on plant roots, transmitting viruses, and facilitating bacterial and fungal infections. Nematode damage may provide an entry point for other plant pathogens to invade the root and further weaken the plant.

Since nematodes are parasites, their feeding not only directly impacts plants, but secondarily impacts plant vigor and defensive characteristics leaving the plant more open to other stressors.

Due to the difficulty involved in precisely identifying nematodes, nematode injury in corn fields is often mistaken for other problems. Damage such as discoloration, stunting and reduction in stalk diameter and root size is often misdiagnosed as herbicide injury, drought stress, disease or micronutrient deficiencies. Although visual symptoms may be mistaken for problems other than nematodes, one thing is for certain: yield and profit potential can be severely impacted. The only way to accurately identify nematode damage is through collection and analysis of soil and root samples at a nematode diagnostic laboratory.

Stunting caused by nematode pressure.
Nematodes: Damage

What damage do nematodes cause? (cont'd)

Though there are some differences in the damage caused by the various species, in general all plant-parasitic nematodes attack corn and reduce corn yields by feeding on and reducing the efficiency of the root system of the plant. Some feed on the outside of the plant roots, some enter the root and feed on plant tissue from the inside, while others employ both methods of feeding.

Plant-parasitic nematodes are efficient feeders, characterized by a hardened pointed mouth spear called a stylet that allows them to pierce plant tissue and feed upon living plant cells.

Root-knot nematode damage.
Lance nematode-affected root vs. healthy root system.
Nematodes: Damage

What damage do nematodes cause? (cont'd)

Yield Loss - Yield loss from nematodes in corn can be substantial. In severe cases, 30 to 50 percent losses have been reported. Nematodes also cause more damage to a crop that is already stressed, especially under drought or limited moisture conditions.

Secondary Damage - In addition to directly harming plants, nematode feeding can result in wounds through which fungi and bacteria can enter the roots and cause secondary rots. Some nematodes also transmit plant viruses.

Stunting in field caused by root-knot nematodes.
Nematodes: Damage

Nematode Symptoms

Whether from primary or secondary damage, nematodes are an important factor in reducing corn yields. The first thing a producer should do if he suspects nematodes is understand the symptoms.

Above-ground symptoms include:

  • Thin stands
  • Uneven plant height
  • Stunted plants
  • Uneven tasseling
  • Leaf yellowing
  • Small ears and kernels

Below-ground symptoms include:

  • Swollen roots
  • Reduced root mass compared to other portions of the field
  • Lack of fine roots and root branching
  • Necrotic lesions or knots on roots
Root-knot nematode damage.
Lesion nematode damage.
Nematodes: Assay

Nematode Assay

Above-ground symptoms are an excellent way to assess the possibility of nematodes, but the only way to confirm an infestation is to take a nematode assay. Nematode assays, in the form of soil sampling, can identify the population levels and nematode species that are in a field.

Soil sampling for nematodes also is important because many of the above-ground symptoms common to these pests could possibly be symptoms of other problems. Only the assay can make the distinction.

Soil sampling can identify the population levels and nematode species that are in a field.
Nematodes: Assay

Soil Sampling Guidelines - Taking the Sample

Soil sampling recommendations may vary from state to state, but there are some basic tips that are universal. Consult your agricultural extension service for information that specifically applies to the state in which you live.

  • First, take at least a dozen or more soil cores to have a complete sample from the areas suspected to have nematodes.
  • Take cores from approximately 8 to 12 inches below the soil surface.
  • Take cores from the root zone of severely affected corn plants.
  • Include as much fiborous root system as possible within samples by pulling soil cores from within the existing crop root zone.
  • Combining cores from poor areas into a poor area sample and then likewise combining cores from healthy parts of the field are composited into a good/healthy area sample.
  • Some nematodes feed inside the roots so take some samples of roots as well.
Take at least a dozen or more soil cores from the areas suspected to have nematodes.
Nematodes: Assay

Soil Sampling Guidelines - Taking the Sample (cont'd)

  • Though recommendations vary in corn, it’s generally best to take samples mid-season.
  • amples should not be taken from parched dry soil or extremely wet soil.
  • Some experts recommend taking a second soil sample from healthy parts of the field to establish a benchmark for comparison purposes.
  • Combine the 12 or more soil cores, representing a sample, together breaking up any large pieces and mix thoroughly.
  • Each sample drawn from the multiple cores should be representative and approximately 1-1.5 pints total volume (or the recommended amount by the nematode analysis lab).
  • Place sample into bag type recommended by the lab to which you are submitting your sample.
Take samples from approximately 8 to 12 inches below the soil surface.
Nematodes: Assay

Proper Documentation of Samples

Establish beforehand where the samples are to be sent – to a private nematode lab or your agricultural extension or research service nematode laboratory. Closely follow their specific directions on how to prepare samples for their use. Each lab may provide a slightly different guidance. Be sure to use the lab's specific speciman submission form so that it includes all the pertinent information your lab requires.

Logging all pertinent background information about the circumstances in the field tested are critical steps in making an accurate assessment of the potential for damage.

  • Make sure the bags are properly identified.
  • Make note of sampling locations, date, cropping history and rainfall.

Without proper documentation, nematode assays alone will not provide enough information to establish a management plan.

Nematodes: Assay

Handling & Shipping of Samples

  • Follow your specific lab's guidance on handling and shipping samples
  • General guidance considerations:
    • After collecting cores and compositing into samples, store in cool and dry location such as an ice chest or refrigerator, but do not freeze.
    • Ship early in the week; do not ship so sample sits on hot truck over a weekend.
    • Best to ship samples overnight, if possible.
    • Never leave samples on a dashboard, in a trunk or bed of a truck where they may be overly heated by direct sun.

Nematode Lab Results Interpretation

Because there are so many different nematodes that attack corn regionally, it is strongly recommended that you review your individual lab's sample analysis report and recommendation that likely depends on the nematode species and the number present. These recommendations will be based on local nematode research on corn production.

Nematodes: Management

Nematode Management

Nothing can be done to rescue your current crop from nematodes. Nematode management can only be implemented ahead of the crop year with a well-planned strategy.

Crop Rotation and Tillage

Rotation to a non-host plant for one or more years can reduce nematode populations. Some nematodes survive longer without a host and require longer rotation sequences.

Non-host rotational crops vary greatly depending on region of the country and the species of nematodes present. Rotation options for a Southeastern producer, for instance, would be substantially different than options available to a Midwestern corn farmer. For example, in the South, peanuts are considered a good rotation crop because they are not hosts for Southern root-knot nematodes. Midwestern fields affected by needle nematodes and/or some species of lesion nematodes can use alfalfa or soybeans as a non-host rotational crop.

Reduced tillage practices can cause nematode populations to increase. Nematodes are aquatic animals, meaning they require free moisture for activity. Increased soil moisture from reduced tillage is a benefit to nematodes.

Nematodes: Management

Impact of Changing Production Practices

Corn nematode populations have escalated in recent years thanks to changes in production practices. In the past, nematode damage was inadvertently suppressed by the widespread use of in-furrow organophosphate and carbamate insecticides. Now, with the switch to pyrethroid insecticides and transgenic CRW-resistant corn, nematode pressure has become more evident as these products lack the ability to suppress nematode growth.

Also, the increased trends in no-till farming and corn-on-corn production have helped provide an environment for nematodes to thrive because these pests are sensitive to soil disturbance.

Nematodes: Management

Seed Treatment

Advancements in formulation and application technology have led to the development of seed treatments for nematodes. The seed treatment form of nematicide offers protection along the roots of developing seedlings and does not require grower application.

Each of the nematode management options described in this tutorial has limitations when used alone. Management practices should be used together in a total management program for the best results, and management strategies should be developed well in advance of the season.

Two corn plants in root-knot nematode-infested soil. The more vigorous plant on the left was treated with a corn seed treatment nematicide.
Untreated root vs. treated root in sting nematode-infested soil.
Seed Treatments

What is Avicta Complete Corn with Vibrance?

Avicta® Complete Corn with Vibrance® nematicide / insecticide / fungicide seed treatment, a combination of separately registered products, gives growers an innovative, seed-delivered technology that works instantly to protect corn seedlings. The result is proven, early-season protection against a wide spectrum of damaging nematode species, insect pests and early-season disease pathogens. That means increased plant stand, uniformity and vigor, stronger emergence and higher yield potential—all delivered in a convenient on-the-seed treatment.

Avicta Complete Corn is available in three different versions that contain varying levels of the insecticide component: Avicta Complete Corn 250 (0.25 mg a.i. / seed of thiamethoxam), Avicta Complete Corn 500 (0.50 mg a.i./seed of thiamethoxam) and Avicta Complete Corn 1250 (1.25 mg a.i. / seed of thiamethoxam).

The addition of Vibrance seed treatment fungicide to the existing Maxim® Quattro 4-way fungicide package in Avicta Complete Corn, provides the most comprehensive, robust corn fungicide package ever offered. This addition brings best-in-class Rhizoctonia protection for stronger, healthier roots, which are critical to maximizing performance and yield.

Avicta Complete Corn with Vibrance gives growers an innovative, seed-delivered technology that works instantly to protect corn seedlings.
Seed Treatments

Unique Protection Against Nematodes

Avicta Complete Corn with Vibrance delivers immediate protection from the moment the seed is planted, promoting stronger stands and emergence, and building the foundation for better yields. Avicta Complete Corn with Vibrance provides protection from a wide spectrum of damaging nematode species including:

  • Root-knot
  • Lance
  • Lesion
  • Needle
  • Spiral
  • Stubby-root
  • Sting
  • Dagger
  • Ring
  • Stunt
Lesion nematodes attacking a corn root.
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Seed Treatments

Enhanced Protection Against Early-Season Insects

Avicta Complete Corn with Vibrance contains thiamethoxam (Cruiser® seed treatment insecticide) for proven early-season insect protection.

Avicta Complete Corn with Vibrance protects corn plants from a broad spectrum of troublesome insect pests, including:

  • Wireworm
  • Southern corn leaf beetle
  • Black cutworm
  • Corn flea beetle
  • Sugarcane beetle
  • Chinch bug
  • Southern green stinkbug
  • Thrips
  • Seedcorn beetle
  • Billbug**
  • Seedcorn maggot
  • White grub*
  • Grape colaspis
  • Corn leaf aphid
  • Corn rootworm**

* Including Japanese beetle larvae, European Chafer larvae, true white grub, annual white grub and May/June beetle larvae.

**Requires the higher application rate of thiamethoxam (1.25 mg a.i./seed) found in Avicta Complete Corn 1250. Corn rootworm protection includes Mexican, Northern, Southern and Western varieties.

Avicta Complete Corn 500 provides an increased rate of insecticide (0.50 mg a.i./seed of thiamethoxam) compared to Avicta Complete Corn 250 (0.25 mg a.i./seed of thiamethoxam) for enhanced insect protection.

Avicta Complete Corn 1250 offers the highest available rate of insecticide (1.25 mg a.i./seed of thiamethoxam) for added insect protection against corn rootworm and billbug, and is a key component in an effective integrated corn rootworm management program.

Seed Treatments

Top-Quality Disease Protection

Avicta Complete Corn with Vibrance also boasts the best disease protection available with a combination of Maxim® Quattro seed treatment fungicide and Vibrance seed treatment fungicide. Together, these fungicides offer five active ingredients for protection against a wide spectrum of damaging early-season diseases: mefenoxam, fludioxonil, azoxystrobin, thiabendazole and sedaxane.

The disease protection of Avicta Complete Corn with Vibrance helps shield the developing plant against reduced emergence that can cause slow growth and damping off of the seedlings, as well as reduced plant stand, vigor and ultimately yield.

The addition of Vibrance brings best-in-class Rhizoctonia protection. Vibrance, which is systemic, protects the root hairs damaged by Rhizoctonia thereby increasing root surface area. This improves water and nutrient uptake, and helps the plant better handle stress.

Avicta Complete Corn with Vibrance protects against the most damaging seed- and soil-borne diseases in corn, including:

  • Mucor
  • Fusarium
  • Cladosporium
  • Helminthosporium
  • Diplodia(Stenocarpella)
  • Aspergillus
  • Penicillium
  • Sporisorium (Sphacelotheca)
  • Rhizopus
  • Rhizoctonia
  • Pythium
  • Fusarium
    • Fusarium graminearum
    • Fusarium verticillioides
  • Macrophomina
  • Diplodia (Stenocarpella)
  • Sporisorium (Sphacelotheca)
  • Penicillium
  • Colletotrichum
The corn root system on the left is a non-infested root and the corn root on the right is infested with Fusarium. Notice the discoloration and the lack of root hairs on the Fusarium infected root. Photo provided by Dr. Wayne Pedersen.
Pythium symptoms in Richland, Iowa hog farm field.
Avicta Complete Corn with Vibrance Benefits

Benefits of Avicta Complete Corn with Vibrance

Seed treatments protect a grower’s seed investment and the value of traits and genetics by protecting the plant when it is most vulnerable, the first three or four weeks after planting. By the time corn reaches the four-to-seven-leaf stage, some yield determination factors, such as the number of kernel rows, are set. There is no rescue treatment for nematodes, so if growers have yield-limiting effects, there is no remedy. Miss the yield window and it is gone. With only an average of 40 total corn harvests in a lifetime, growers need to get it right from the start.

Avicta Complete Corn with Vibrance offers corn growers a wide array of benefits including:

  • Proven protection against a wide spectrum of damaging nematode species, insect pests and early-season pathogens
  • Interaction of a nematicide, insecticide and fungicides, for superior early-season pest protection, as well as optimal yield and profit potential
  • Protection for root hairs that are damaged by Rhizoctonia which helps increase the root surface area, thereby improving the plant’s ability to absorb water and nutrients, and better manage stress
  • Convenient on-the-seed delivery; just plant and the crop is protected
  • Vigorous and healthy corn seedlings from the day seeds are planted
  • Proven consistency across broad environmental conditions, including various temperatures, moisture levels and soil pH levels
  • Increased stand, uniformity and vigor
  • Instant performance and as a true nematicide, a way to kill nematodes
Planting seeds treated with Avicta Complete Corn with Vibrance will help protect against nematodes, early-season insects and disease for a healthier and more uniform stand.
Avicta Complete Corn with Vibrance Benefits

The Proof is in the Field

In 42 trials across three years, Avicta Complete Corn 250 had a 4.0 bu/acre advantage over CruiserMaxx® Corn 250.

CruiserMaxx Corn 250 is an on-seed application of Cruiser 5FS insecticide delivered at the 0.25 mg/a.i. seed rate, and Maxim Quattro fungicide.
Avicta Complete Corn with Vibrance Benefits

The Proof is in the Field (cont'd)

In 84 non-inoculated comparisons (lower disease pressure), Vibrance showed on average nearly 2 bu/acre improvement in yield.

Avicta Complete Corn with Vibrance Benefits

The Proof is in the Field (cont'd)

In seven Rhizoctonia inoculated locations (high disease pressure), Vibrance showed more than a 9 bu/acre increase.

Quiz

Please take a moment to complete this quiz. Then, the tutorial will be complete.