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ATTRA By Martin Guerena NCAT Agriculture Specialist © 2006 NCAT A Publication of ATTRA - National Sustainable Agriculture Information Service ã 1-800-346-9140 ã This publication provides general information on the tiny worm-like organisms called nematodes. It contains detailed descriptions of the genera of nematodes that attack plants, as well as various methods to diagnose, discourage, and manage plant parasitic nematodes in a least toxic, sustainable manner. Nematodes: Alt
  A Publication of ATTRA - National Sustainable Agriculture Information Service ã 1-800-346-9140 ã ATTRA—National Sustainable Agriculture Information Service is managed by the National Cen- ter for Appropriate Technology (NCAT) and is funded under agrant from the United StatesDepartment of Agriculture’s Rural Business-Cooperative Ser- vice. Visit the NCAT Web site  ( html) for more informa- tion on our sustainable agriculture projects.   ATTRA  Contents By Martin GuerenaNCAT AgricultureSpecialist© 2006 NCAT Nematodes:Alternative Controls  This publication provides general information on the tiny worm-like organisms called nematodes. It contains detailed descriptions of the genera of nematodes that attack plants, as well as various methods to diagnose, discourage, and manage plant parasitic nematodes in a least toxic, sustainable manner. Introduction N ematodes aretiny, worm-like, multicellular animals adapted to liv-ing in water. The num- ber of nematode species is estimated at half a million, many of whichare “free-living” typesfound in the oceans,in freshwater habitats,and in soils. Plant-par-asitic species form a smaller group. Nema-todes are commonin soils all over theworld (Dropkin, 1980;Yepsen, 1984). As a  commentator in the early twentieth century wrote: An important part of the soil fauna, nem-atodes live in the maze of interconnectedchannels—called pores—that are formedby soil processes. They move in the fi lmsof water that cling to soil particles. Many genera and species have particu lar soil and climatic requirements. For example, cer-tain species do best in sandy soils, whileothers favor clay soils. Nematode popula- tions are generally denser and more preva- lent in the world’s warmer regions, where longer growing seasons extend feeding peri- ods and increase reproductive rates (Drop- kin, 1980). In the southern United States, as many as ten generations are produced in one season (Yepsen, 1984). Light, sandy soils generally harbor largerpopulations of plant-parasitic nematodesthan clay soils. This is attributable to Introduction .....................1Symptoms andSampling .......................... 4Preventing FurtherSpread of Nematodes .......................4Managing SoilBiology ...............................5Crop Rotations andCover Crops ......................6BotanicalNematicides .....................9Biocontrols......................10Plant Resistance ............11Red Plastic Mulch .........12Solarization ....................13Flooding ..........................13Summary .........................13References .....................14Further Resources ........17Web Resources ..............17Suppliers ..........................18 If all the matter in the universe except the nematodes were swept away, our world would  still be dimly recognizable, and if, as disembod- ied spirits, we could investigate it, we should find  its mountains, hills, valleys, riv ers, lakes and  oceans represented by a thin film of nematodes. (Sasser, 1990) Root-knot nematode— Meloidogyne brevicauda Loos ©Jonathan D. Eisenback, Virginia Polytechnic Institute and State University  Page 2 ATTRA  Nematode: Alternative Controls BiointensiveIntegrated PestManagementSustainable SoilManagementSustainableManagement of Soil-Borne Plant DiseasesAlternative SoilAmendmentsManures for OrganicCrop ProductionOverview of CoverCrops and GreenManures Related ATTRAPublications more ef  fi cient aeration of sandy soil, fewerorganisms that compete with and prey onnema todes, and the ease with which nem-atodes can move through the root zone.Also, plants growing in readily drained soils are more likely to suffer from intermit- tent drought, and are thus more vulnerable to parasitic nema todes. Desert valleys andtropical sandy soils are particularly chal- lenged by nematode overpopulation (Drop- kin, 1980). Plant-parasitic nematodes—the majority of which complete their lifecycles in the rootzone and feed upon the roots—are foundin association with most plants. Some areendoparasitic—living and feeding within the tissue of roots, tubers, buds, seeds, etc. (Sasser, 1990) Others are ectoparasitic,feeding externally through plant walls. Asingle endoparasitic nematode can kill a plant or reduce its productivity, while sev- eral hundred ectopara sitic nematodes might feed on a plant without seriously affectingproduction (Ingham, 1996). A few spe-cies are highly host-speci fi c, such as Het- erodera glycines on soybeans and Globodera rostochiensis on potatoes (Sasser, 1990).But in general, nematodes have a wide host range. Endoparasitic root feeders include sucheconomically important pests as the root-knot nematodes ( Meloidogyne species),the cyst nematodes ( Heterodera species),and the root-lesion nema todes ( Prat-  ylenchus species). (Sasser, 1990) Important ectoparasitic root feeders include: root (Paratrichodorus and Trichodorus) , dag-ger (Xiphinema) , needle (Longidorus,Paralongidorus) , ring (Criconemella, Mac-roposthhonia) , stunt (Tylenchorhynchus and  Merlinius) , pin (Paratylenchus) , and spiral (Helicotylenchus, Rotylenchus, and Scutello- nema) nematodes. Direct feeding nematodes can drastically decrease a plant’s uptake of nutrients and water. Nematodes have the greatest impact on crop productivity when they attack the roots of seedlings immediately after seed germina-tion (Ploeg, 2001). Nematode feeding also creates open wounds that provide entry to a  wide variety of plant-pathogenic fungi andbacteria. These microbial infections are often more economically damaging than the direct effects of nematode feeding. Nematode control is essentially prevention,  because once a plant is parasitized it is impossible to kill the nematode without also destroying the host. The most sustainable Major Plant-Parasitic NematodeGenera in the U.S. and AssociatedDamage to PlantsRoot-knot   nematodes (Meloidogyne species) form gallson injured plant tissue. The gallsblock water and nutrient flow to the plant, stunting growth,impairing fruit production, and causing foliage to yellow and wilt.Roots become rough and pimpled and susceptible to cracking. Cyst   nematodes (Heterodera  species) give plants an unthrifty or malnourished appearance, and cause them to produce smaller-than-normal tops. Foliage is lia-ble to wilt and curl, while rootsbecome thick and tough and takeon a red or brown coloring. Sting nematodes (Belonolaimus  species) are found mainly in theSouth, especially in sandy soilswith meager organic-matter content. Areas of stunted plantsare an early indicator. As theseareas grow larger and finally meet, the plants that were first affected will start to die at themargins of older leaves. Root-lesion (Pratylenchus species) cause internal brown-ing in potato tubers and in theroots of corn, lettuce,peas, carrots,tomatoes, and brassicas.(Yepsen, 1984) ãããã  Page 3  ATTRA N ematodeshave thegreatest impact on crop pro-ductivity when they attack the roots of seedlings immedi-ately after seed germination. ©  Ulrich Zunke, ©  William Wergin, www.mactode.comSpiral nematode, Helicotylenchus sp.Pratylenchus sp. larva and egg. ©   Jonathan Eisenback,  ©  Michael McClure, www.mactode.comFace view of lance nematode, Hoplolaimus sp.Sugarbeet cyst nematode juvenile. ©  Ulrich Zunke, www.mactode.comLesion nematodes penetrating a root.Mononchoid nematode feeding on another nematode.  ©   Jonathan Eisenback,  Page 4 ATTRA  Nematode: Alternative Controls approach to nematode control integrates several tools and strategies, including covercrops, crop rotation, soil solarization, least- toxic pesticides, and plant varieties resistant to nematode damage. These methods work best in the context of a healthy soil envi-ronment with suf  fi cient organic matter to support diverse populations of microorgan- isms. A balanced soil ecosystem supports a wide variety of biological control organisms that helps keep nematode pest populations in check. Symptoms and Sampling Usually, sampling is done because thegrower observes a section of field with unhealthy plants, or notices an unexplained yield reduction. Be cause nematodes dam-age roots, any condition that stresses the plant—such as drought (or even hot spells), fl ooding, nutrient de fi ciencies, or soil com- paction—will tend to amplify the damagesymptoms noted above. Failure to respond normally to fertilizers and slower-than-nor- mal recovery from wilting are signs of nem- atode infes tation. In the undisturbed soil of groves, turf, and pastures, visible symp- toms of nematode in jury normally appear as round, oval, or irregular areas in the plant- ing that gradually increase in size year byyear. In cultivated land, nematode-infesta- tions are often elongated in the direction of  cultiva tion, because nematodes are moved by machinery. (Dunn, 1995) It is important to note that species of nem-atode are present in all soils; their merepresence does not necessarily mean thatthey are damaging plants. Harmless or even bene fi cial species are found in proxim- ity to plants, right along with the parasitic species. Bene fi cial nematodes feed on such pests as Japanese beetle grubs and plant-parasitic nematodes, and release nutrientsinto the soil by eating bacteria and fungi(Ingham, 1996; Horst, 1990). An experi-enced nematologist can iden tify species,and determine which, if any, are responsi- ble for the observed damage. Nematode sampling techniques varydepending on the crop, the root depth, thetype of nematode causing damage, and the time of the season. The procedure pre- sented here is a generic sampling technique for annual crops. Soil samples taken inthe late summer are best when testing forthe presence of nema todes. Root-zone soilsamples are best taken im mediately afterharvest, or just prior to harvest if the crop shows signs of damage. First, fi elds should be divided into 20-acre blocks with similar damage, soil texture, or cropping history. From each block take several sub-samples, mixing them well to create a single one-quart sample for each block. Soil samples should be kept cool, but not frozen. Samples for established perennial crops are best taken from the feeder root zone, which is usually located around the canopy dripline (Dropkin, 1980). Your county or state Cooperative Extension Service can providenames of commercial labs that have nema- tode-identi fi cation services. Preventing Further Spreadof Nematodes Preventing nematodes from entering unin-fested areas is important; under their ownsteam they can spread across a  fi eld at a rate of three feet per year. The following measures will help prevent human-assisted spread of nematodes to uninfested fi elds:Use certi fi ed planting material Use soilless growing media in green- houses Clean soil from equipment beforemoving between fields (washingequipment—including tires—with water is most effective) Keep excess irrigation water ina holding pond so that any nema-todes present can settle out; pumpwater from near the surface of thepond; plan irriga tion to minimize excess wa ter Prevent or reduce animal movement from infested to uninfested fi elds Compost manure to kill any nema- todes that might be present, before ãããããã I t is important tonote that spe-cies of nema-tode are present inall soils.
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