Nematodes in Cotton

Nematode damage has historically been attributed to poor fertility or poor soil conditions. Research has led to a better understanding of nematode identification and the yield losses that nematodes can cause. Nematodes can damage roots and limit root growth, leaving cotton plants susceptible to environmental stress, insect damage, and diseases.  

Root-Knot Nematode 

 
Pathogen and Range 
 

Damage to cotton by root-knot nematodes (RKN) are caused by Meloidogyne species, including the southern root-knot nematode (M. incognita), northern root-knot nematode (M. hapla), and guava root-knot nematode (M. enterolobii). Root-knot nematodes infect a wide range of plant hosts, including many that are potential crop rotation options for cotton growers. Soybean, corn, tobacco, sorghum, sweet potato, several vegetable crops, and multiple weed species can be potential hosts for RKN, complicating management options. 

Root-knot nematodes live in the soil and feed on young roots. Females live inside the roots and produce egg masses that range from 500 to 3,000 eggs. The eggs hatch under moist conditions, and juveniles spread through soil water and enter root tips. A single root tip can contain as many as 20 juveniles. Damage to the roots results from chemical changes caused by RKN feeding that can enlarge root cells up to ten times their normal size. These large cells prevent the root from developing and taking up the water and nutrients the growing plant needs. The damaged and enlarged roots form galls that resemble knots. During the growing season, the RKN lifecycle completes every four to six weeks. Root-knot nematode development is greatly slowed or stopped when soil temperatures are below 50˚F or above 100˚F.1,2  

Figure 1. U.S. counties in which the presence or absence of root-knot nematodes has been verified in cotton plots. Data courtesy of the National Cotton Council. Figure 1. U.S. counties in which the presence or absence of root-knot nematodes has been verified in cotton plots. Data courtesy of the National Cotton Council.
Symptoms

Root-knot nematode (RKN) infested areas of a field are not uniformly distributed, and cotton plants growing in these areas may be chlorotic and stunted (Figure 2). Infected plants can wilt by midday due to the inability of damaged roots to take up water. Damage to the roots can lead to secondary infection by bacteria or fungi. Root-knot nematodes produce visible galls on the roots of cotton plants. Symptomatic plants can be carefully dug up and soil gently removed to reveal galls on infected roots (Figure 3). 1.2  

Figure 2. Chlorotic and stunted plants in an area of a cotton field with root-knot nematodes. Figure 2. Chlorotic and stunted plants in an area of a cotton field with root-knot nematodes.
Figure 3. Galling on cotton roots infected by root-knot nematodes. Figure 3. Galling on cotton roots infected by root-knot nematodes.
Diagnostic Notes 
 

Root-knot nematode populations are often lowest at planting and highest at cotton plant maturity. Survivability can be very low during the winter, with up to 99% of RKN individuals unable to survive freezing conditions. However, their ability to reproduce during warm conditions can increase the RKN population more than 100 times between planting and harvest.2  

Root-knot nematode populations are more commonly found in coarse-textured, sandy soils.RKN may be found in the same fields as Columbia lance nematode, but is usually not found with reniform nematodes, unless corn is used in the crop rotation sequence.3

Fields with RKN can increase the incidence and severity of Fusarium wilt, if present. In general, fields without RKN require 100 times more inoculum of the Fusarium pathogen to cause the same damage as fields with RKN. The Fusarium wilt/root-knot disease complex often leads to large areas of dead plants, which normally would not occur with either Fusarium wilt or RKN alone. The severity of some root rots may also be higher in the presence of RKN.2  

Potential Yield Loss and Control 
 

Cotton plants can tolerate a small amount of RKN damage without negatively impacting yield. However, this is related to the availability of nutrients and water as well as the exposure to insects and diseases.   

Soil sampling for nematodes should be completed around harvest, when nematode populations are typically at their highest. The following article can provide more information on the procedure for sampling for nematodes in cotton, Cotton Nematode Predictive Sampling and Prevention.  

Nematodes are present in the soil of infected fields and can be disseminated to non-infested fields by soil on equipment, trucks, or shoes. Sanitation is important to prevent the spread of nematodes to other fields. If possible, work in fields known to have nematodes last.1

Root-knot nematodes can be managed by planting an RKN-resistant variety, through crop rotation, and with the application of nematicides. Root-knot nematode-resistant varieties provide protection throughout the season. Fields can be rotated to a non-host crop like peanut or a soybean product that is resistant to RKN. Nematicides are also available and should be applied pre-plant or at planting.  

Reniform Nematode 

 
 
Pathogen and Range 
 

Female reniform nematodes in the genus Rotylenchulus penetrate the root cortex to establish a feeding site. Once established, the reniform nematode is immobile and remains embedded in the root. Females lay 60 to 200 eggs, with eggs hatching one to two weeks later. Reniform nematode juveniles (larvae) are infective and penetrate roots one to two weeks after hatching. Reniform nematodes can survive without a host in dry soils for two years.4

R. reniformis, the reniform nematode species that invades cotton, can be found in the Southeast, the Midsouth, and Texas. Soybean, sweet potato, tobacco, several vegetables (including tomato, okra, and squash), and weed species are hosts of reniform nematodes, complicating control.4

Figure 4. U.S. counties in which the presence or absence of reniform nematode has been verified in cotton plots. Data courtesy of the National Cotton Council. Figure 4. U.S. counties in which the presence or absence of reniform nematode has been verified in cotton plots. Data courtesy of the National Cotton Council.
Symptoms
 

Reniform nematodes can cause plant stunting; however, this can be difficult to observe as distribution is usually uniform throughout the field. Carefully digging up the plant may reveal grainy, small roots. This is a result of sand sticking to the egg masses.  

Diagnostic Notes
 

Reniform nematodes are typically found in silty soils, and populations tend to peak around 60% to 65% sand content and decline when the sand content is higher than 65%.5 The presence of reniform nematodes may increase the incidence of seedling diseases.3 Populations are usually uniformly spread across the field, and soil sampling can confirm the presence of reniform nematodes.  

Potential Yield Loss and Control 
 

Yield loss attributed to reniform nematode pressure in untreated fields can be up to 59%.

Reniform nematodes can be managed by selecting varieties resistant to reniform nematodes. Rotating fields to corn for one to two years can help reduce nematode populations. Nematicides can help reduce populations and can be applied as seed treatments, through fumigation, and as soil or foliar sprays. 

Columbia Lance Nematode 

 
 
Pathogen and Range 
 

Columbia lance nematode (CLN), Hoplolaimus columbus, has a more limited range than root-knot or reniform nematodes. CLN presence has been primarily documented in North Carolina, South Carolina, and Georgia, but CLN has also been found in Alabama, Florida, and Louisiana. Cotton, corn, and soybean are hosts of CLN, but planting these in rotation can help control CLN populations when compared to continuous cotton production.5

CLN is a migratory nematode, meaning that it remains mobile in the soil rather than attaching to a root and staying there. Females lay eggs that hatch roughly 12 days later, and CLN complete their lifecycle and feed on cotton for an additional 33 days. Ideal soil temperature for reproduction is 92˚F. CLN can survive in the soil for over a year and overwinter as eggs, larvae, or adults.7

Figure 5. U.S. counties in which the presence or absence of lance nematodes has been verified in cotton plots. Data courtesy of the National Cotton Council. Figure 5. U.S. counties in which the presence or absence of lance nematodes has been verified in cotton plots. Data courtesy of the National Cotton Council.
Symptoms 
 

Columbia lance nematode (CLN) damaged cotton roots have necrotic lesions and affected plants will be severely stunted. Damaged plants are usually found in patches that may be oval-shaped in the direction of tillage.8

Figure 6. Cotton roots damaged by either lance or sting nematodes. Photo courtesy of Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org. Figure 6. Cotton roots damaged by either lance or sting nematodes. Photo courtesy of Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org.
Diagnostic Notes 
 

Early-season infection leads to the most significant damage, as CLN feed on tap root and secondary root tips. Plants may have more root branching in the upper four inches of soil (Figure 6). The incidence of seedling diseases and Fusarium wilt may be increased with CLN infection.8

In fields with both RKN and CLN, the presence of CLN can often suppress RKN populations. However, the distribution of these nematodes can be influenced by soil texture. Both species prefer coarser, sandier soils. The preference for sandy soils results in plants growing in only certain areas of a field being affected by CLN instead of uniform distribution throughout a field.

Potential Yield Loss and Control 
 

Damage thresholds are generally 75 CLN per 100 cm3 of soil. Yield losses typically range between 10% to 25% and yield losses over 50% are possible. 

Rotation with peanut, a non-host, can help reduce CLN populations. Limit moisture and nutrient stress. In-row subsoiling can help reduce symptom expression by promoting root development, but subsoiling does not decrease CLN populations.8 The patchy presence of CLN can make a uniform application of a nematicide expensive. Targeted applications based on soil test results or soil texture can be used to reduce cost.5  

Sting Nematode

 

 

Pathogen and Range
 

The sting nematode, Belonolaimus longicaudatus, is a migratory nematode that remains mobile in the soil. Females lay eggs in pairs and can produce 10 eggs every 10 to 15 hours. Juveniles hatch after a few days and feed on root hairs followed by root tips. They are very large, two to three times longer than CLN, and prefer soils with a sand content of 85% or higher. This limits their range to coastal plain soils in Florida, North Carolina, South Carolina, Georgia, Virginia, Alabama, and Mississippi. Corn, sorghum, soybean, and several vegetable crops are hosts of sting nematode, with tobacco and peanut as exceptions.7,9  

Symptoms 
 

Sting nematode damage to cotton roots often shows as visible lesions on the root surface. Feeding may lead to the production of tiny roots (Figure 6). The inability to take up water and nutrients leads to wilting, stunting, chlorosis, and death (Figure 7).Feeding can damage the root meristem and suspend root growth, resulting in “stubby” roots.9

Figure 7. Spotty plant growth in an area of a field affected by sting nematode (left) and severe stunting (right). Photos courtesy of Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org.
Cotton plant affected by sting nematode.

Figure 7. Spotty plant growth in an area of a field affected by sting nematode (left) and severe stunting (right). Photos courtesy of Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org. 

Diagnostic Notes 
 

The presence of sting nematode may increase the incidence of Fusarium wilt. 

Potential Yield Loss and Control 
 

Crop rotation to peanut or tobacco can help reduce the population level of sting nematode. Nematicides are very effective against sting nematode; however, the nematodes can migrate deep within the soil profile and escape fumigation.9 

 
 
 
Sources  

1 Thiessen, L. and Rivera, Y.R. 2019. Root knot nematode of cotton. NC State Extension. https://content.ces.ncsu.edu/cotton-root-knot-nematodes

2 Wrather, A. and Sweets, L. 2009. Cotton nematodes in Missouri: Your hidden enemies. University of Missouri Extension. G 4249. https://extension2.missouri.edu/g4259

3 Understanding cotton nematodes. National Cotton Council of America. https://www.cotton.org/tech/pest/nematode/ucn.cfm

4 Wang, H. 2019. Reniform nematode. University of Florida. EENY-210. http://entnemdept.ufl.edu/creatures/nematode/r_reniformis.htm

5 Holguin, C.M., Mueller, J.D., Khalilian, A., and Agudelo, P. 2015. Population dynamics and spatial distribution of Columbia lance nematode in cotton. Applied Soil Ecology. 95: 107-114. 

Dyer, D.R., Groover, W., and Lawrence, K. 2020. Yield loss of cotton cultivars due to Rotylenchulus reniformis and the added benefit of a nematicide. Plant Health Progress. 21:113-118. 

Koenning, S.R., Kirkpatrick, T.L., Starr, J.L., Wrather, J.A., Walker, N.R., and Mueller, J.D. 2004. Plant-parasitic nematodes attacking cotton in the United States. Plant Disease. Vol. 88, No.2:100-113. 

8 Blasingame, D., Gazaway, W., Kemerait, R., Kirkpatrick, T., Koenning, S., Lawrence, G., McClure, M., Mueller, J., Newman, M., Overstreet, C., Phipps, P., Rich, J., Thomas, S., Wheeler, T., and Wrather, A. 2003. Cotton nematodes - your hidden enemies. Beltwide Cotton Nematode Research and Education Committee. http://cotton.tamu.edu/.  

9 Crow, W.T. 2015. Sting nematode. University of Florida. http://entnemdept.ufl.edu/creatures/nematode/sting_nematode.htm.  

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