Nematodes are often overlooked as a pest in corn due to their small size and non-distinctive damage symptoms, but they are capable of causing significant yield loss by damaging corn roots.
Nematodes may be becoming a greater threat to corn due to changing production practices.
Visual symptoms of nematode damage are usually apparent in "hot spots" in the field. Plants may appear to be moisture-stressed, stunted, and chlorotic.
Many different nematode species can cause yield loss in corn. Damage in a field can be caused by a single species or by several.
The only way to confirm that symptoms are being caused by nematodes and not some other stress factor is by submitting a sample of soil and root tissue for testing.
Crop rotation and tillage may help reduce nematode populations, depending on which species are present.
Pioneer Premium Seed Treatment choices for corn include Poncho® 1250 + VOTiVO®. This treatment provides a broad spectrum control of corn soil insects, plus the added protection of VOTiVO for corn nematodes.
Nematodes are a well-known pest of soybean, but are frequently overlooked as a cause of yield loss in corn. Corn nematodes are difficult to detect due to their small size, and the symptoms they cause often resemble symptoms of common stress factors such as drought or nutrient deficiencies. Today, however, there is a growing realization that nematodes can and do economically affect corn.
Over 50 species of nematodes are known to feed on corn in the U.S., several of which can cause significant economic damage. Corn nematodes are commonly characterized as a pest specific to sandy soils, such as in Kansas and Nebraska and the coastal plains of North and South Carolina. While this is true of some species, other species can exist in a range of soil conditions. No field is immune to the potential for nematode damage.
Nematodes normally do not kill plants but act as parasites on the host plant. If plant death did occur, nematodes would be more obvious and of more concern to growers. Instead, these microscopic roundworms often increase without being detected. This trait has earned them the reputation of "silent yield robbers" of corn.
Are Nematodes Becoming More Common?
The capability of nematodes to damage corn has been known since the 1950s, however recent trends in farming practices may be increasing nematode numbers as well as their economic importance as corn pests. Reduced tillage is known to favor some nematode species, as is corn following corn. These rootworm insecticides also had some activity against nematodes, whereas newer alternatives such as pyrethroid insecticides and transgenic rootworm-protected corn do not. Additionally, our ability to sample and diagnose nematode damage has improved. Symptoms that may have previously been attributed to some other stress factor are now correctly being traced to nematodes.
Nematodes are the most abundant multicellular organisms on earth, and are ubiquitous across a wide range of ecosystems. Nearly 20,000 species have been described, although the biology of most species is poorly understood. Most species are microscopic, typically ranging from 0.25 to 3.0 mm in length, although some species are much larger.
Nematode Life Cycle
The life cycle of corn nematodes is similar to other nematodes – juveniles hatch from eggs and pass through multiple larval stages to the adult stage. Both juvenile and adult nematodes feed on the roots of the host plant. The length of time required to complete a life cycle varies widely among species, from several days up to a year.
Nematodes are notable in that juveniles hatch in a "unisex" form and their sex is determined later in life. Those that become males move through the soil and probably don't contribute to plant damage, according to the scientific literature. Those that become female nematodes feed and reproduce additional nematodes as the life cycle begins anew. The eggs that females produce are the overwintering structure for these organisms.
Plant parasitic nematodes are typically soil-borne and feed on plant roots. Nematodes use a stylet to pierce the corn root and remove life-sustaining nutrients. However, nutrient loss is only one of the negative effects of nematode feeding. In addition, tissue damage at the feeding site provides easy entry into the root system by commonly associated root pathogens.
Corn Nematode Feeding Habits
Ectoparasites – Nematodes live in the soil and feed on the surface of root tissue by inserting the stylet into cells within reach.
Migratory endoparasites – Nematodes completely penetrate the plant tissue and remain mobile, feeding as they move through the plant tissue. They spend most of their lifecycle in the plant tissue, but can also be found in the soil.
Sedentary endoparasites – Nematodes enter the plant tissue and develop a permanent feeding site.
Semi-endoparasites – Nematodes partially enter plant tissue, leaving the rear part of their bodies projecting into the soil.
Visual Symptoms in Corn
Nematodes frequently remain undetected as a cause of plant injury. Their small size makes them virtually invisible and the damage they cause is often overlooked or mistaken for some other plant stress factor. However, if nematode numbers have increased to the point that they are causing economic damage, visual symptoms are usually apparent in "hot spots" in the field. These visual symptoms are similar to those often associated with soil compaction. Plants may appear to be moisture-stressed, stunted and chlorotic, or exhibit less extreme signs of generally poor plant growth. These symptoms are often mistaken for another problem, such as low fertility, weather stress, or insect or disease pressure.
Root symptoms may vary, as may above-ground symptoms. Root pruning is usually evident, as well as proliferation of fibrous roots, thickening or swelling of the smaller roots, and mild to severe discoloration.
Most often these symptoms don't appear over a very wide portion of the field. No specific patterns are usually identifiable with nematode damage, although as the problem grows, it often moves in the direction of field tillage. This is due to the physical movement of the nematodes with soil in tillage operations.
Corn Nematode Species
Nematodes are similar to weeds and insect pests of corn in that there are many species of nematodes with varying biological characteristics that are capable of reducing corn yield. Different soil environments will favor different nematode species. A given field may have only a few economically important species present, or it may have many. See Appendix Table 1 for a species summary.
Lesion Nematodes (Pratylenchus spp.)
Although not the most damaging type of nematode, lesion nematodes are considered to be the most important genus to Midwestern corn production due to their prevalence. Lesion nematodes are widespread, and population densities of 10,000 nematodes/cm3 of soil are not uncommon. This genus prefers sandy soil, but is found in a wide range of soil types. There are 6 species in this genus that are known to feed on corn. Lesion nematodes are migratory endoparasites that alternately feed and move within the root tissue. Symptoms include severe root pruning resulting in stunting, chlorosis, and discoloration. Crop rotation has been shown to be effective at reducing lesion nematode numbers.
Needle Nematodes (Longidorus spp.)
Needle nematodes are the most devastating type of corn nematode in the Midwest, but are much less prevalent than lesion nematodes, being confined strictly to sandy soils. Needle nematodes are relatively large at 4 to 5 mm long, and the greater pore space in sandy soil is necessary to accommodate their size. Yield reduction can be severe, exceeding 60% in the most extreme cases. Corn roots will appear stubby due to pruning of the finer roots, and the above-ground portion of the plant will appear stunted, with symptoms resembling drought stress.
Lance Nematodes (Hoplolaimus spp.)
Lance nematodes are also very potentially damaging. Like needle nematodes they are relatively large (approx. 1.5 mm), making sandy soil their most suitable habitat. They are not limited to sandy soil however, and can be found in a wide range of soil types. Lance nematodes have a wide host range, which can limit the effectiveness of crop rotation as a means of control. At least four Hoplolaimus species are known to affect corn. H. galeatus is prevalent throughout the U.S. and is the most common lance nematode in Midwestern corn fields. H. columbus, commonly known as Columbia lance nematode, is common in southern states where it can also be a damaging pest in soybean and cotton.
H. galeatus can exist in a range of soil types, whereas H. columbus is much more limited to sandy soil. Lance nematodes are initially ectoparasitic, but can partially or completely penetrate the root tissue. Lance nematodes cause stunting in corn early in the season which results in spindly plants with reduced yield at harvest.
Dagger Nematodes (Xiphinema spp.)
Dagger nematodes are another relatively large type of nematode, making them favored by, but not limited to, sandy soil. Dagger nematodes have a wide host range and are important pests in many other crops, most notably grapes and other fruits. One species, X. americanum, is known to have a very long lifecycle. This species reproduces once per year and can live 4 to 5 years in undisturbed soil with favorable conditions. Crop rotation is not an effective means of control for dagger nematodes; however tillage may disrupt their lifecycle and help reduce population numbers. Feeding on corn roots by dagger nematodes can cause stunting and chlorosis.
Root-Knot Nematodes (Meloidogyne spp.)
Root-knot nematodes are sedentary endoparasites that spend the majority of their lifecycle inside the root tissue. There they form small galls on the roots. Root-knot nematodes are favored by sandy soil. Multiple species of root-knot nematodes affect varying ranges of host crops throughout North America, so effective management requires knowledge of the specific species present. Of the four most common species, corn is a host for three. Root-knot nematodes generally have a wide host range, which limits the effectiveness of crop rotation as a means of control. Alfalfa and oats are non-host crops that may be rotated with corn to reduce populations; however soybeans are a host crop and can be damaged even more than corn, particularly in the southern U.S. The southern root-knot nematode (M. incognita) is a serious pest of cotton, and rotation with corn can increase the chances of cotton yield loss. Research has shown resistance in certain corn inbreds and hybrids, however most current hybrids are not resistant to root-knot nematodes.
Sting Nematodes (Belonolaimus spp.)
Sting nematodes are found in the sandy plains of the Atlantic and Gulf coast states, as well as sandy areas in Midwestern states including Kansas and Nebraska. They are ectoparasites that feed on the outside of roots without attaching to or penetrating the root tissue. Feeding occurs at the tips and along the sides of the roots and can result in girdling and death of the root. Injured areas will appear blackened and sunken. Sting nematodes are very large (approx. 3 mm) and are restricted to soils with at least 70% sand. They can be very damaging, however, particularly when stubby-root nematodes are also present. Sting nematodes have a wide host range, including soybean and cotton.
Stubby-Root Nematodes (Paratrichodorus minor)
Stubby-root nematodes can be a very serious pest, but are limited to sandy soils. They are common to the same areas as sting nematodes, in the sandy plains of the Atlantic and Gulf coast states and sandy areas in the Midwest and Pacific coast. Stubby-root nematodes are ectoparasites that feed on the root tips resulting in short, stubby roots which can resemble herbicide damage. Affected plants will be stunted and yellow and may show magnesium deficiency. Corn is the preferred host of stubby-root nematodes; however, they have a wide host range including many other crop species such as cotton, soybean, and sunflower.
Spiral and Stunt Nematodes (Heliocotylenchus spp. and Tylenchorhynchus spp.)
Spiral and stunt nematodes are very widespread in the Midwestern U.S. Three species of spiral nematode are known parasites of corn. Unlike many nematodes, they favor heavier soils rather than sand. Spiral nematodes are named for their characteristic spiral body shape when inactive. Stunt nematodes also tend to favor heavier soils Both species are ectoparasitic and can cause damage to corn when populations are large or in conjunction with other nematode species, however yield loss in corn is rare. Other host species include soybean, clover, and turfgrass.
Ring, Sheath, and Pin Nematodes (Criconemoides spp., Hemicycliophora spp., and Paratylenchus spp. )
Ring, sheath, and pin nematodes are all sedentary ectoparasites that tend to feed at a single site on the surface of the root tissue. Ring and sheath nematodes are rare in cultivated crops and more commonly parasitize perennial plants in undisturbed soil. Ring nematodes tend to favor sandy soil, whereas pin nematodes are very small and prefer finer-textured soil.
Other Important Nematode Species
Soybean Cyst Nematode (Heterodera glycines)
The soybean cyst nematode undoubtedly is the most widely known nematode species in the Corn Belt. Although many nematode species can damage soybean, soybean cyst nematode is by far the most important. Soybean cyst nematode does not pose a threat to corn.
Corn Cyst Nematode (Heterodera zeae)
The biology of the corn cyst nematode is similar to that of the soybean cyst nematode. Its first discovery in North America was in Maryland in 1981. Fields known to be infested in Maryland and Virginia were quarantined from 1981 until 1996. Since the lifting of the quarantine, H. zeae has not been confirmed in any other state. It is known to have a higher optimal temperature than the soybean cyst nematode, which may limit the suitability of fields in the Corn Belt as a host environment.
A new corn cyst nematode species was found in Tennessee in 2006. Research conducted so far has confirmed that this species is different from H. zeae, and shown that corn is a favorable host, whereas dicot species such as soybean are not. Whether this species will spread as a pest of corn is unknown.
Reniform Nematode (Rotylenchulus reniformis)
The reniform nematode is a serious pest of cotton in the southern U.S. Soybean is also susceptible to reniform nematodes, however corn is not.
Sampling for nematodes is similar across species. Growers should sample when nematode numbers are highest. This is often at the beginning of the second trimester of the growing season. Allowing the crop to become established and the nematodes to hatch and begin feeding helps ensure that juveniles and adults are at their peak populations. Healthy plant tissue is vital to successful nematode survival. For this reason, nematodes are easier to find in an early- to middle-aged crop than in fallow fields.
There are four samples suggested for fields potentially infested with nematodes. A sample should be taken from:
the affected area to send to the nematode lab
an "unaffected" area to send to the nematode lab
the affected area for standard soil nutrient testing
an "unaffected" area for standard soil nutrient testing.
A great deal of soil is not needed for a nematode sample. Specific recommendations from your local lab should be followed, but keep these ideas in mind:
Digging affected plants with a spade and including some soil with the roots is often suggested.
Only a cup or two of soil is needed for analysis and this is best taken from within the row of the growing crop.
Clearly label all samples.
Overnight or same-day delivery is best for sample transfer to the nematode-testing laboratory.
Nematodes are one problem that will not go away if ignored. If damaging levels of corn nematodes are found, implementing control measures such as rotation, sanitation or use of nematicides should be considered.
Rotation to non-host crops is the most economical method of controlling some species of corn nematode, such as lesion and needle nematodes. Eliminating alternate hosts during the non-corn growing seasons is important. Weeds may serve as alternate hosts for some nematode species, so effective weed management is important in rotated crops. Some nematode species have a wide host range and will not be affected by crop rotation, so it is important to know which species are present in a field. Growers are encouraged to check with local university extension sources for a list of local alternate host crops and weeds.
Pioneer Premium Seed Treatment choices for corn include Poncho® 1250 + VOTiVO®. According to the product label, this treatment provides a broad spectrum control of corn soil insects, plus the added protection of VOTiVO for corn nematodes. VOTiVO contains a unique strain of bacteria that lives and grows with young corn roots, creating a living barrier that helps protect corn seedlings and roots against nematodes.
In the past, some growers used an in-furrow insecticide/nematicide for control of corn nematodes, others in extreme situations used a fumigant. Some chemicals or even biological products are now being used as seed treatments. New methods and materials are continuously being discovered and labeled for use. Some materials are lethal to nematodes, some act to disorient them and others may provide a protective barrier between the nematode and the plant as a food source.
Growers can keep up to date on labeled materials and uses at Pioneer field days and winter meetings. The newsletter, "Walking Your Fields®" provided by local Pioneer Account Managers, is one way to keep abreast of current and effective ways of using specific pesticides for managing nematodes or other pests for a specific area.
Because nematodes cannot be eradicated once they are established in a field, prevention is a critical management strategy. Common-sense sanitation procedures can prevent movement of nematodes from known areas to uninfested fields or field areas. Equipment should be cleaned with high pressure water or steam to remove all soil particles before moving to an uninfested area. Field operations should be conducted last in infested areas if possible.
Anon. 1997. The Ectoparasitic Nematodes of Illinois. University of Illinois Extension Report on Plant Disease No. 1106. Urbana, IL.
Crow, W. T., and A. S. Brammer. 2008. Lance Nematode, Hoplolaimus galeatus (Cobb, 1913) Thorne, 1935 (Nematoda: Secernentea: Tylenchida: Tylenchoidea: Hoplolaimidae) University of Florida Extension Publication: EENY234. Gainsville, FL.
Crow, W. T., and A. S. Brammer. 2008. Sting Nematode, Belonolaimus longicaudatus Rau (Nematoda: Secernentea: Tylenchida: Tylenchina: Belonolaimidae: Belonolaiminae). University of Florida Extension Publication: EENY239. Gainsville, FL.