Soybean nematode control

John D. Mueller

Nematode losses in South Carolina soybeans are caused primarily by Southern root-knot, soybean cyst, Columbia lance, and reniform nematodes.  Sting, lesion, and peanut root-knot nematodes also cause losses in some fields.  Soybean is an excellent host for these nematode species and therefore often sustains significant yield losses. 

Fig. 1. Dead, stunted, and chlorotic plants caused by root-knot nematode.

In a survey of 500 soybean fields in South Carolina more than 90% of the fields had one of the previously listed nematode species present.  Almost a third of the fields had at least one nematode species at damaging levels.                                                               

Symptoms caused by nematodes typically include stunted or yellow plants.  Patches of damaged plants are typically oval in the direction of tillage in a field.   By the time this level of damage is detected nematodes are usually prevalent in the field and are causing greater than a 20% yield loss. 

Therefore detection of a nematode problem prior to symptom development is highly desirable.  The reniform nematode typically does not produce such distinct symptoms.  Only root-knot nematode produces diagnostic symptoms (root galls) that can be easily seen with the unaided eye.  Even then you cannot be sure if you have Southern or Peanut root-knot nematode or if another nematode species is present. 

The only accurate way to determine if nematodes are causing a problem in your field is by submitting a soil sample to a nematode laboratory.  There are two basic types of nematode samples.  The first is a predictive sample.  This sample is taken in the Fall and used to predict the degree of yield loss that may occur in the crop the following year. 

A predictive sample will determine the density of each nematode species present.  These numbers can then be compared to values that are associated with known levels of yield losses (see Table 1).  The second type of nematode sample is a diagnostic sample.  These samples are taken during the growing season to determine if areas of poor growth, stunting, or chlorosis are due to nematodes or some other problem. 

Nematode problems are so common in South Carolina that a nematode sample should be included in almost any attempt to diagnose the cause of poor growth in a field.

Samples can be submitted through your county agent to the Clemson University Agricultural Services Laboratory.  The charge is $10.00 per sample.  Since most samples represent 10 to 20 acres this is an investment of $0.50 to $1.00 per acre to determine if you can avoid losing 25 to 50% of your yield.  The optimum time to sample for nematodes is from three weeks prior to harvest until three weeks after harvest. 

A typical nematode sample should consist of one sample for each field or 10 acre section of larger fields.  Break fields up into obvious sections as determined by soil types, drainage or cropping history.  Use a shovel or soil probe to get soil from the crop row to a depth of about 8 inches.  Each sample should be composed of 10 cores mixed together in a bucket.  A 1-quart composite sample should be placed in a plastic bag, sealed and labeled. 

 When submitting a diagnostic sample it is advisable to include some live crop roots in the sample, especially if species determination of root-knot nematode is being requested. 

 Results from predictive samples include control recommendations based on the nematode species and population levels that are found.  A nematode assay will allow you to select the most appropriate resistant varieties, plant effective cropping systems, and make decisions on when to use a nematicide.

 Table 1.  Damage thresholds for nematode species in corn, cotton and soybean in typical Coastal Plains soils in South Carolina.  Thresholds are per 100 cm³ soil.      

The five nematode genera that cause soybean yield losses, their symptoms and controls are described in the following paragraphs.

      Distribution:  Root-knot nematodes can occur in almost all of the Coastal Plains soils and even in some of the lighter Piedmont soil types.  There are several species of root-knot nematode that can affect soybean in South Carolina.  The most important species is "Southern" or "common" root-knot nematode.  This is Meloidogyne incognita.   A second species also occurs in South Carolina.  It is race two of the "peanut" root-knot nematode, Meloidogyne arenaria.  Race one of Peanut root-knot nematode goes to peanut but is very rare in South Carolina.  Race two goes to soybean but not peanut, and is common in the Lexington County area. Both M. incognita and M. arenaria occur in the northeast corner of the state where tobacco has been grown.  Other species such as M. hapla, the Northern root-knot nematode and M. javanica have been detected sporadically in the state.

      Symptoms:  Damage from root-knot nematode can be severe, including death of infected plants.  Damage levels increase as the plants are exposed to moisture or heat stress.  Affected soybeans can be stunted and yellow.  They may not die until later in the growing season when they are full grown and most susceptible to moisture stress.  Roots usually exhibit visible galls.  Galls should not be confused with Rhizobium nodules.  Galls are an integral part of the root; nodules are not.  If you run your fingers down a root pinching the root as you go nodules will pop off but galls will stay. 

      Control measures:  The most cost-effective way to control root-knot nematodes is to use resistant varieties or to rotate to a non-host crop.  Most soybean cultivars exhibit only partial resistance to Southern root-knot nematode and may not provide enough control where pressure is heavy or where other nematode species are also present.  Table 1 gives threshold values for Southern root-knot nematode in soybean.  Where pressure is low to moderate resistant cultivars should provide sufficient control.   Where Southern root-knot nematode densities are high (2 to 3 times the threshold or more) the field should be rotated to a non-host crop (Table 2) or a nematicide should be added to the resistant cultivar (Table 4). 

If a nematicide is used it should always be applied to a root-knot nematode resistant cultivar.  Susceptible cultivars may respond to a nematicide, but typically yields of a susceptible cultivar plus a nematicide will be less than those of a resistant cultivar without a nematicide. The most cost effective response to a nematicide is typically on a resistant cultivar.  In-row subsoiling or any other cultural practice that helps reduce stresses can help limit damage due to root-knot nematodes.  Nonhost crops that will reduce nematode population densities are listed in Table 2.

Table 2.  Host status of common row crops in South Carolina to commonly occurring nematode species.  Growing the non-host species will reduce nematode levels in a field. 

     Distribution:  The Columbia lance nematode (Hoplolaimus columbus) occurs in most soybean growing areas of the state.  Due to its large size it is restricted to sandier soils with larger pore sizes.  Hoplolaimus galeatus is also common in South Carolina but occurs primarily in perennial plants such as turf.  It is rarely seen in cotton or soybean fields. 

     Symptoms:   Affected plants can be stunted and yellow, but plants usually do not die.  Damage is often exhibited as uneven (up and down) growth in the row.  Roots are sometimes bunched near the soil surface and show poor taproot development.  Roots may also have a hairy or fibrous appearance (with many small rootlets).  Rhizobium nodulation may be poor.

     Control:  Try to use a cultivar tolerant of Columbia lance nematode.  In-row sub-soiling will reduce, but not eliminate, losses from Columbia lance nematode in most Coastal Plain soils.  Planting early, prior to mid-May can reduce losses.  However, later planting dates such as those in a wheat/soybean double-cropping system may favor infection and damage by Columbia lance nematode.  Therefore, avoid double-cropping soybeans in Columbia lance nematode fields.  Use a low rate of a nematicide at planting on a tolerant cultivar (see Table 4).  Crop rotation is normally not effective since peanut is the only nonhost crop (Table 2).  Soil-borne diseases such as red crown rot (black root-rot on peanut) build up under soybean and cause serious problems in subsequent peanut crops. 

     Distribution:  The soybean cyst nematode (Heterodera glycines) occurs throughout the Coastal Plain and the lower Piedmont counties.  Unlike many nematode species it is not limited to specific soil types. 

    Symptoms:  Affected plants are usually stunted and have yellow leaves.  Close examination of the roots may show reduced nodulation and tiny white to yellow cysts.  The optimum time to find cysts is to view roots 30- to 45-days after planting.  These cysts are the females of the cyst nematode.  Do not confuse cysts with nodules.  Cysts are much smaller and harder to see.  Mature cysts (females) slough off the roots, the eggs hatch and young cyst larvae continue the life cycle, which takes about 30 days to complete.  Where soybean cyst is suspected in a field, have the soil tested for nematodes. 

   Cyst Nematode Races:  There are 16 possible races of soybean cyst nematode.  These races vary in their ability to infect and reproduce on different sources of genetic resistance in the plant.  Currently race 3 is the most common race in South Carolina followed by race 14 and then races 6 and 9.  If a race 3-resistant variety shows symptoms, have the soil tested for nematodes. 

If the results indicate that cyst nematode is the only problem nematode present, chances are good that race 14 or another race is present.  Several varieties are available commercially with resistance to races 3 and 14.  Avoid planting a race 14-resistant variety on your farm until race14 cyst nematode is identified as the problem.  The use of race 14-resistant soybean varieties prior to the detection of race 14 in a field may result in a natural selection of races for which there are no resistant soybean varieties.

     Control:  Soybean cyst nematode is easily spread in soil clinging to equipment, runoff water, blowing dust, or soil peds that may contaminate seed.  Make sure seed for planting are free of all foreign matter.  Clean all equipment before moving from an infested field, or even a suspected field, to another field.  Avoid monocropping soybeans, especially the same cultivar.  Rotation with a non-host crop such as corn, cotton, peanut, or sorghum will greatly reduce inoculum for the next year's crop (see Tables 2 and 3).  Where soybean cyst nematode infestations are severe two years of a non-host crop may be needed.  Always take soil samples prior to using a susceptible soybean variety to be sure cyst nematode populations are well below the damage threshold.  

Table 3.  Rotation schemes for soybean cyst nematode management in South Carolina.

A nematicide can be used for cyst nematode management, especially if other harmful nematodes are present in the field: see Table 4. Yield potentials and commodity prices must be high to justify the use of Telone II.  However, three gallons per acre of Telone II will provide excellent control of most nematode species present. Three to five lbs per acre of Temik 15G can be used at planting to help control nematodes.  Only use Temik 15G with a resistant cultivar.  If Temik 15G is used on a susceptible cultivar yields may not be as high as with a resistant cultivar alone. 

Continuous use of SCN-resistant varieties in the same field may cause a buildup of a new race for which resistance is not available.  For this reason, do not use a resistant variety on an SCN-infested field for more than two consecutive years.

Use of a wheat-soybean double-cropping system may reduce cyst nematode populations.  The high soil temperatures at the late planting date for the soybeans in this system are detrimental to cyst nematode.  However, later planting dates may favor infection and damage by Columbia lance nematode.

     Distribution:  Reniform (Rotylenchulus reniformis) nematode is a commonly occurring problem in the counties between the Santee lakes and the North Carolina border.  It is also common in Calhoun and Orangeburg Counties.  In the early 1980's reniform nematode was thought to be restricted to clay soils and river bottoms.  Today we know that reniform nematode can occur in most of our Coastal Plains soils and possibly in some Piedmont soils.  Reniform has a relatively wide host range and cotton is an excellent host (Table 2). 

     Symptoms:  Reniform typically produces the least distinctive damage of any of the nematode species on soybean.  Reniform populations build up rapidly and instead of oval areas containing damaged plants the entire field will be stunted or discolored.   Stunted areas typically are where the soil type is poor and plants are under stress even without nematode damage.

     Control: Soybean varieties with resistance to cyst races 1 and 3 may also be resistant to reniform nematode.  A one year rotation with a non-host crop will usually reduce the population density to a level where a reniform nematode susceptible soybean variety can be grown.  However, in some cases the populations of reniform nematode are so high it takes a two-year rotation to lower the population sufficiently. Use of nematocide may help to reduce yield losses due to reniform nematode (Table 4).     

      Distribution:  Sting nematodes (Belonolaimus spp.) are usually restricted to only the sandiest soils.   

     Symptoms:  Very low populations of sting nematode can cause extensive damage on soybean (Table 1).  Severe stunting and chlorosis are common.   

      Control:  The host range for sting nematode includes corn, coastal Bermuda grass, cotton, okra, peanut, soybean, and watermelon.   No non-host crops are available for rotation (See Table 2).  In-row subsoiling is a must.  Use of a nematicide may help (See Table 4).   

 Table 4.  Nematicides available for use controlling Soybean Cyst, Southern Root-Knot, Columbia lance, Reniform, Sting, and Lesion nematodes.

Page maintained by: Pawel Wiatrak, pwiatra@clemson.edu