Dorchester County, Md., Extension Agent Betsy Gallagher takes soil samples as part of a SARE-funded 

project seeking to reduce root-damaging nematodes 

in potatoes and soybeans.

Agricultural Innovations

Cultural Practices for Root-Knot and Root-Lesion 

Nematode Suppression in Vegetable Crop Rotations

Introduction

Growers of vegetable crops in the mid-Atlantic have typically used nematicides to control root knot nematodes 

(RKN) and root-lesion nematodes. The loss of many nematicides from the market due to environmental concerns and constraints of use, such as the length of the period when crops 

cannot be planted following application for currently labeled 

fumigant nematicides, have focused attention on the development of alternative methods for managing plant parasitic 

nematodes.

This publication discusses the use of non-host crops, sorghum 

sudangrass and castor bean grown as cover crops, RKNresistant crops, and the application of poultry litter (PL) and 

PL compost to manage RKN and root-lesion nematode. These 

methods can be used in vegetable production systems to reduce build-up of nematodes over time, to lengthen the interval 

between nematicide applications and to provide a nonchemical management approach for organic growers. Examples of different cultural practices for managing RKN and root

-lesion nematodes are shown in Table 1. 

The southern RKN and root-lesion nematode are prevalent in 

Maryland and Delaware and cause severe damage in areas 

with sandy soils. The southern RKN damages a wide variety 

of crops grown throughout the mid-Atlantic region including 

soybeans and tobacco, and vegetables such as sweet potatoes, 

tomatoes, potatoes, cucumber and green beans. Fields cropped 

repeatedly to these crops have experienced significant losses 

due to RKN. Corn and wheat, common crops in the region, 

are reproductive hosts for RKN. 

Inside this fact sheet:

# Introduction

# Nematode Sampling Procedures

# Cover Crops and Nematode Management

# RKN-Resistant Crops and Nematode 

 Management

# Poultry Litter (PL) and PL Compost and

 Nematode Management

# SARE Research Synopsis

SARE Agricultural Innovations are based on 

knowledge gained from SARE-funded projects. 

Written for farmers and agricultural educators, 

these peer-reviewed fact sheets provide practical, 

hands-on information to integrate well-researched 

sustainable strategies into farming and ranching 

systems. The articles are written by project 

coordinators and published by SARE.

The cultural practices described in this publication were 

evaluated for nematode control in field and small plot 

studies in Maryland. The practices described in this fact 

sheet should be effective in mid-Atlantic vegetable crop 

production systems where the southern root-knot nematode is the most important root-knot species and where 

growing season and crop rotations are similar to Maryland’s Eastern Shore. 

GE O G R A P H I C RA N G E :

Fact Sheet Practical applications for

sustainable agriculture

PDF available at www.sare.org/publications/factsheet/pdf/06AGI2005.pdf

Sustainable Agriculture Research & Education

Robert Kratochvil

Dept. of Natural Resource Sciences 

and Landscape Architecture, 

University of Maryland

Kathryne Everts

Dept. of Natural Resource Sciences 

and Landscape Architecture, 

University of Maryland

University of Delaware

Sandra Sardanelli

Dept. of Entomology

University of Maryland

L. Betsy Gallagher

Dorchester County Extension, 

University of Maryland
Cultural Practices for Root-Knot & Root-Lesion Nematode Suppression in Vegetable Crop Rotations SARE 2

Root-lesion nematode also has caused severe damage on potato and cucumber, although yield losses due to root-lesion 

nematode are highly variable and influenced by environmental conditions. In addition, when the fungus Verticillium 

dahliae is present with root-lesion nematode, potato early 

dying disease occurs.

Symptoms of plant damage due to nematode activity may 

initially appear similar to lack of or improper fertilization, too 

little or too much water, improper soil pH, poor soil, or other 

environmental factors. Irregular patches in the field with poor 

plant growth (sickly growth, wilting, yellowing, stunting and 

premature plant aging) can range from a few feet to hundreds 

of feet across. Losses due to nematodes may be more prevalent than is currently known

Growers who use nematicides to control root-knot and rootlesion nematode on potatoes and cucumbers incur large expenses. For example, 25% of the pickling cucumber acreage in 

Maryland and Delaware was fumigated in 1998, a typical 

year. 

Maryland potato growers met in the fall of 1999 and expressed interest in alternative strategies such as cover crops, 

non-host rotation crops and poultry manure for managing 

parasitic nematodes in the potato cropping system. The research and management tactics described in this publication 

were developed as a result of that meeting.

Suppressive cover crops and nematode-resistant rotation 

crops have been reported to significantly reduce nematode 

populations in agricultural soils in trials conducted in other 

regions of the U.S. 

Poultry litter (a mixture of poultry manure and pine shaving 

bedding) and composted poultry litter also have been used as 

an organic soil amendment to suppress root-knot nematodes 

and provide an alternative to nematicides. The breakdown of 

poultry litter (PL) or PL compost stimulates microbial activity in the soil that suppresses nematode damage and reduces 

population densities. 

Table 1. Potential cropping sequences to minimize damage from root knot nematode in the mid-Atlantic.

Symptoms of RKN infection on a cucurbit root. 

Year 1 Year 2

Crop 1 Crop 2 Amendment Winter 

Cover 

Crop

Crop 1 Crop 2 Amendment Winter 

Cover 

Crop

Potato Soybean

„Manokin‟

None Oat Cucumber Soybean

„Manokin‟

None Oat

Potato Castor

bean

None Oat Cucumber Castor

bean

None Oat

Potato Sorghum 

sudangrass

None RapeseedCucumber Sorghum 

Sudangrass

None Rapeseed

Potato Sorghum 

sudangrass

7000 lb/A 

poultry litter

Oat Cucumber Sorghum 

sudangrass

7000 lb/A poultry litterOat

Potato Sorghum 

sudangrass

10,500 –

31,000 lb/A 

poultry litter 

compost

Oat Cucumber Sorghum 

sudangrass

10,500 –

31,000 lb/A 

poultry litter 

compost

Oat
Cultural Practices for Root-Knot & Root-Lesion Nematode Suppression in Vegetable Crop Rotations SARE 3

Nematode Sampling Procedures

Proper management of root-knot and root-lesion nematodes 

begins with timely sampling of fields. Sampling soil in the 

spring is not reliable because few nematodes may be detected 

even in fields where the risk of potential damage is high. This 

is probably because inadequate degree-days have accumulated during the spring for nematode reproduction to occur. 

Samples collected in late summer or early fall are much more 

reliable. During the growing season, diagnostic samples may 

be taken whenever symptoms are observed.

Recommended sampling procedures are to collect soil cores 

or soil samples (if using a shovel) from a depth of 6-8 inches 

from at least 20 representative locations across the field. Soil 

core locations should target areas where the crop appears 

stunted, chlorotic or weak, and nematode damage is suspected. A field may be divided into sections for sampling purposes if either known or observed differences for nematode 

damage are present across the field. A minimum of one pint 

of soil is required per sample area for analysis. Root samples 

of both crop and weed plants that are present in the field 

should be submitted with the soil sample. Samples can be 

submitted to County Extension Educators or directly to either university or private nematode diagnostic laboratories 

for analysis.

Laboratory analysis will provide the proper identification of 

the plant-parasitic species and an estimate of the number of 

each nematode species that are present.

Cover Crops and Nematode 

Management

Use of cover crops is increasing in the mid-Atlantic region 

because they have been proven to reduce soil erosion 

and nutrient loss and improve soil health. Additionally, reductions in soil-borne and foliar disease may 

result from cover crop use. Nematode-suppressive 

cover crops provide the additional benefit of nematode disease suppression. 

Two non-host cover crops that can be grown in the 

mid-Atlantic and may provide root-knot nematode 

population reduction are sorghum sudangrass and 

castor bean. In cropping system experiments in 

Maryland, sorghum sudangrass grown annually as a 

green manure crop following a nematode–

susceptible potato or cucumber crop reduced the 

RKN population as effectively as a nematicide application prior to production of a susceptible soybean 

cultivar. An annual green manure crop of castor 

bean also significantly reduced RKN, but 

annual inclusion of these crops is necessary 

to maintain reduced populations. In addition, results may be 

variable (i.e. the nematode suppressive effect is not observed 

every year) due to other environmental influences upon the 

nematodes.

Field procedures

Sorghum sudangrass cv. ‘Green Grazer’ (AgriBiotech Brand, 

Inc.) can be planted following an early season vegetable crop 

such as potato, processing cucumber, pea or snap bean. Planting seed at 20 lb/acre in mid to late July produced adequate 

biomass to suppress RKN. For best suppression, the sorghum 

sudangrass crop should be chopped and incorporated into the 

soil in mid October. (Note: Although we used cv. ‘Green 

Grazer’, research throughout the U.S. has shown that other 

varieties also should work well.)

Castor bean cv. ‘Mall’ grown for green manure is seeded at a 

relatively low density-11,500 seeds/acre in mid to late July 

following spring vegetable crop production. Again, approxiSwelling on the surface of a potato infected 

with root-knot nematode. 

Cover crops grown in micro-plots (note castor bean at left, and sorghum 

sudangrass at right, in the foreground).
Cultural Practices for Root-Knot & Root-Lesion Nematode Suppression in Vegetable Crop Rotations SARE 4

mately three months of growth should produce adequate biomass to suppress nematodes. Castor bean should be mowed 

or chopped and the biomass tilled into soil in mid October. 

Table 2 provides planting dates and seeding rates for these 

cover crops in Maryland. 

RKN-Resistant Crops and Nematode 

Management 

Planting an RKN-resistant crop that can be harvested is a 

tactic that would allow growers to reduce nematode levels 

while still producing a marketable crop. The soybean cv. 

‘Manokin’ (maturity group late IV-S) has resistance to RKN. 

Annual cropping of ‘Manokin’ resulted in consistent reduction in RKN detected in soil assays and less root galling (an 

indication of nematode damage) compared to roots of susceptible soybean cultivars. Because root galling is directly related 

to nematode reproduction, planting ‘Manokin’ or other RKNresistant soybean cultivar should reduce RKN populations 

and improve crop performance over time. 

While use of RKN-resistant soybeans has potential, it is important to choose cultivars that have maturity group ratings 

appropriate for the geographic region where they will be used 

as a double crop. In addition, ‘Manokin’ is susceptible to rootlesion nematode and therefore cannot be used alone for management in fields with a mixed species infestation of parasitic 

nematodes. Use of soybean or vegetable crops that are RKN 

resistant offer an economically attractive strategy for vegetable crop growers.

Field procedures

When grown as a double crop option, seed soybean cv. 

‘Manokin’ at 175,000 seeds/acre following harvest of an early 

season vegetable crop. Maturity of ‘Manokin’ requires that it 

be planted no later than late June – early July if it is to be harvested for grain. 

Soybean may be 

used as forage, if 

season length 

does not allow 

grain harvest. 

Following harvest, a non-host 

(or poor host) 

crop for parasitic 

nematodes such 

as oat or rapeseed can be 

planted.

Crop Planting Date Seeds/A Incorporation 

Date

Comments

Resistant soybean10 July – 2 August1250,000 N/A „Manokin‟ is resistant to RKN and 

SCN. However, it is susceptible to 

root-lesion nematode. Therefore, 

use this practice where root-lesion 

nematode is not a problem.

Castor bean 10 July – 2 August 11,500 –

24,500

25 Sept – 19 Oct. Nematode suppressive effect was 

observed in some, but not all, environments. This may be a difficult 

crop for many farmers to incorporate 

into production.

Sorghum sudangrass10 July – 2 August 200,000 25 Sept – 19 Oct Nematode suppression is not observed every year. Suppression is 

enhanced by addition of poultry litter 

compost.

Rapeseed 9 – 27 Oct 861,400 12 Mar – 18 Apr This crop is planted in the “offseason” and because of timing may 

not replace a cash crop.

Table 2. Production practices for nematode–suppressive crops in Maryland. 

Brown discoloration beneath the potato 

skin at the site of a RKN infection.
Cultural Practices for Root-Knot & Root-Lesion Nematode Suppression in Vegetable Crop Rotations SARE 5

Poultry Litter (PL) and PL Compost 

and Nematode Management

In mid-Atlantic vegetable fields, more than one species of 

parasitic nematode often are present; therefore, strategies to 

minimize damage from more than one species are necessary. 

Castor bean and the RKN-resistant soybean ‘Manokin’ reduce 

RKN populations and root galling. However, only sorghum 

sudangrass reduces RKN and also root-lesion nematode. In 

addition, incorporation of poultry litter (PL) or PL compost in 

combination with production of sorghum sudangrass as a 

cover crop provided the most consistent reduction in rootlesion nematode, although variation in the response did occur 

across years. This variation was likely due to:

1) Differences in soil environments across locations and years 

that impact microbial or nematode activity, or 

2) The generation of nematicidal compounds in response to 

organic amendments.

Addition of PL or PL compost may result in longer-lasting 

nematode suppression than cover crops alone. For example, 

carry-over suppression of nematodes was observed where PL 

compost was combined with a sorghum sudangrass cover 

crop. Combining a cover crop with addition of PL that has 

been composted prior to application will mitigate nutrient loss 

potential in fields prone to runoff.

Field Procedure

Amendments of PL or PL compost may be applied in mid 

July following early season vegetable crop harvest and before 

a cover crop is planted. Effective rates varied from 2,500 lb to 

7,000 lb/acre PL and 10,500 lb to 31,000 lb/acre PL compost.

SARE Research Synopsis

With funding from Northeastern SARE, trials were conducted in small plots and on grower fields to evaluate cultural 

methods to manage RKN and root-lesion nematode. Meetings 

with Maryland and Delaware producers of potatoes and other 

vegetable crops led to the selection of 12 three-year rotational 

sequences for evaluation in small plots and six three-year rotations to evaluate on two farms in Dorchester County, Maryland. The experimental locations all were infested with RKN 

(Meloidogyne incognita) and root-lesion nematode 

(Pratylenchus penetrans). Experiments in small plots and on 

growers’ fields were arranged as a randomized complete block 

design with seven and four replications, respectively.

Early season sampling (i.e. April or May) was determined to 

be too early for detection of damaging levels of RKN or rootlesion nematode. Summer or early fall sampling dates effectively identified fields that exceeded threshold levels of the 

two nematodes.

The field and micro-plot experiments demonstrated that, 

while not consistent, RKN resistant soybean ‘Manokin’ or 

sorghum sudangrass grown annually as a green manure cover 

crop could reduce RKN compared to the control treatment of 

an RKN susceptible soybean. ‘Manokin’ or castor beans 

grown as a cover crop and incorporated as green manure reduced RKN by 60% or greater in the fall of 2000 and 2001. 

Sorghum sudangrass, which was grown as a cover crop and 

incorporated as green manure, reduced RKN by 50% or more 

in 2001. In addition to reductions in RKN in the soil, cucumber root-knot indices were reduced in 2001. This reduction 

occurred where sorghum sudangrass was grown and amended 

in the fall of 2000 with 2,500 lb/acre PL or 31,000 lb/acre PL 

compost.

Likewise, high rates of PL and PL compost alone or in combination with sorghum sudangrass also led to a reduction in root

-lesion nematode – though not in all years. Reductions in rootlesion nematode were observed only in 2001 and when grain 

sorghum (with no amendment) or sorghum sudangrass 

amended with 2,500 to 7,300 lb/acre PL or with 10,500 to 

31,000 lb/acre PL compost reduced root-lesion nematode by 

70% or more compared to a grower standard treatment. However, the cover crop, PL or PL compost treatment effect generally did not carry over to the following year and therefore 

cover crop and PL and PL compost amendment needs to be 

included annually.

This fact sheet is based on a SARE-funded project. 

For more information, please visit www.sare.org > 

Project Reports >Search the database 

for project # LNE00-131

SARE Publication #06AGI2005

Root-knot nematode female and, for size comparison, 

the head of a pin.