CONTROL OF PLANT PARASITIC NEMATODESAROUND THE HOME AND GARDEN

C. Wendell Horne and Jerral D. Johnson*

L-781

Plant parasitic nematodes, slender wormlike ani­mals that move among soil particles and root surfaces,attack numerous ornamental and garden plants as wellas lawn grasses. They are too small to be seen by thenaked eye; however, their damage is apparent instunted, unproductive plants.

Nematodes puncture plant cells and withdrawjuices with a hollow stylet in their forepart. Enzymes(digestive juices) secreted into plant cells to predigestfood often cause abnormal responses detected as rootknot galling, the most common symptom observed byhomeowners.

Root knot nematode damage is most noticeable tothe observer, but other nematode types cause plantdamage just as severe with less obvious symptoms.These include a stubby root condition, dead areaswithin roots, excessively branched roots or death of anentire root branch. Roots should be dug and not pulledfrom the soil when symptoms are sought. It maybe necessary to wash soil from roots to see more defi­nite symptoms.

After preparing for observation, compare sus­pected roots with healthy plant roots to enable cleareridentification of nematode symptoms. If plants arelegumes such as beans and peas, do not confuse nitro­gen nodules caused by nitrifying bacteria with rootknot nematodes. Nitrogen nodules, attached to theside of the root, can be removed by the thumbnailwithout destroying the root. However, root knot gallsare formed within the root and cannot be removedwithout root destruction.

Nematodes are commonly introduced into anoninfested area by bringing in contaminated soil orplanting infested transplants. Sterilization of soil or

*Extension plant pathologists, The Texas A&M University Sys­tem.

mulch before placing in flower beds or gardens willprevent nematode occurrence. Transplants intro­duced into the area should have been grown insterilized or nematode-free soil.

Spear used in puncturing plant cells

Fig. 1. General shape of a nematode. They mayrange in length from 0.2 mm to 10 mm J but mostplant parasitic types -range below 2 mm.

19.5

Texas Agricultural Extension Service. The Texas A&M University System. Daniel C. Pfannstiel, Director. College Station, Texas

Table 1. Chemical control information

Soil may be sterilized physically or chemically.Small amounts may be treated in an oven at 160 de­grees F for 3 to 4 hours. Higher temperatures causerelease of toxic substances in the soil. Steam steriliza­tion with steam generation equipment is satisfactory ifsoil is well tilled and covered with an airtight coverbefore steam exposure. Time required for adequatesteam sterilization may be determined by placing araw Irish potato under the cover at the beginning ofthe operation. When the potato is baked throughout,sterilization is complete.

One chemical control option is available forhomeowner use. Vapam®, a soil fumigant-type chem­ical can be used as a preplant soil treatment on smallareas where no living plants are present (see Table 1).

Table 2. Reaction of certain ornamental plants to root knotnematodes

August. This practice is most effective if rainfall is lowand temperatures are high. Do not expect eradica­tion, since nematode eggs are not as susceptible as thefree living stage.

BoxwoodAjugaZinniaSnapdragonHollyhockCape jasmineMorning gloryPetunia

Heavily damaged

PeriwinkleVirbenaSweetpeaAnnual phloxPansyDay lillyIrisPhloxWisteriaSasanquaEuonymousLigustrumPittosporium

Moderately affectedLeast affected

Dwarf yauponLiriopeEnglish ivyTrailing lantanaBambooPampas grassRussina oliveJuniperCherry laurelDogwoodAmerican hollyCrape myrtleWax myrtleChinese tallowBox elderDeodora cedarSycamoreMost oaks

Avoid relying on control methods such as growingmarigolds or using sugar in the soil since they areineffective and may cause secondary problems. Usingrecommended procedures saves time and money andavoids disappointment.

Suggestion for use

Use on well tilled soil which is freeof large clods. For most effectivecontrol the soil should be from60-90 degrees F with moistureideal for planting. Avoid too wet ordry soil. DO NOT USE WHEREROOTS OF LIVING PLANTS ARELOCATED. Apply with water atthe labeled rate. Sprinkle im­mediately with V2 in. of water tomove the material down in thesoil. Repeat water application 2additional days to maintain thewater seal and move the materialfurther down into the soil. Cover­ing with a plastic film is optional.WAIT 3 WEEKS BEFORE PLANT­ING.

Material and characteristics

Vapam® is a toxic liquidwith an offensive odorwhich reduces the chanceof exposure. It is safe foruse around the home land­scape and garden. Followlabel directions.

Alternative control methods vary in their effec­tiveness. When available resistant varieties can beused successfully to avoid damage. Resistant varietiesare not available for most ornamental and gardencrops (see Tables 2 and 3).

In home vegetable gardens use summer fallowingto reduce nematode populations. To be most effectivetill the soil thoroughly in late July and again in early

Facts About Plant Parasitic NematodesRelated to Their Occurrence and Control

ematodes are capable of moving only about 1foot per year by their own motion; therefore, theymust rely on movement of soil, water or plant mate­rial for major distribution. Cultural practices of soiltillage and transplanting result in the inadvertentmovement of nematodes. Soil clinging to tillageequipment is one of the most common means of dis­tribution.

Table 3. Home garden crops and their reaction to root knot nematodes

Least affected Moderately affected* Heavily damaged

Tomatoes - Resistant varieties only such as Big Set,Bonus, Better Boy, Terrific, Jack Pot or Small Fry

Asparagus

Onions

Garlic

Corn

Southern Peas - Resistant varieties only such asMississippi Silver and California Cream NO.5

Cabbage

Radishes

Turnips

Tomatoes - All varieties without proven resistance.

Potatoes, Beans, Peas, Beets, Okra, Cucumber, Can­taloupe, Carrots

*Damage escape is due mostly to their being grown during the cool season. All may have some galling of the root system.

Fig. 2. Root knot galls on lima beans. Galls areproduced as a result of feeding and presence of thenematode inside the roots.

Sinc nematodes are aquatic animals they mustresid in moist soil or plant material. Tilling the soilregularly during summer months and exposing it toheat and drying reduce populations considerably. Donot exp ct to eradicate nematodes by cultural orch mical means. A combination of suggested controlpractic reduces nematode numbers so that a suc­ce ful crop can be grown.

Plant parasitic nematodes usually can be found asde p in the soil as roots penetrate. This insures thatno control procedure will be completely effective.

F ding and reproductive rates of nematodes are

faster during warm temperatures, but may be sus­pended almost completely in cold soil. Som wintergarden crops such as cabbage and onions often pro­duce well even though there is some nematod dam­age.

Growing susceptible crop specie continuously in­creases nelnatode populations to the point wh r itbecolnes virtually ilnpossible to produce a su c ptiblecrop. Grow less susceptible crop in rotation withmore susceptible type .

ematodes that feed on plants are obligat para­sites which do not survive and reproduce without thepresence of a suitable host plant. Depriving thesenematodes of a host plant for 1 or 2 years usually isadequate to reduce the population to a very low I vel.Certain weeds and grasses can serve, however, as hostplants. If not controlled, they can Inaintain the popu­lation.

Some feel that nematode populations develop ifsusceptible crops are grown. This is not the case. De­velopment occurs only if nematod s are present in­itially or have been introduced to th new growingsite.

ematodes can be controlled so that desired cropscan be grown by using cultural and chemical controlmethods.

Detecting the Presence ofPlant Parasitic Nematodes

The Plant ematode Detection Laboratory at Col­lege Station will process soil samples for $2 per sam­pIe. If this service is desired, contact your countyExtension Agent for form number D-827 which re­quests certain information and gives instructions fortaking the sample. Take about 1 pint of soil from theroot zone. It should be moist when collected and notpermitted to dry. Place in a plastic bag and protectfrom excess heat. Mail to the Plant Nematode Detec­tion Laboratory in the Plant Sciences Building atTexas A&M University at College Station, Texas77843. Make checks payable to the Texas AgriculturalExtension Service.

Homeowners with growing plants can detect thepresence of root knot nematodes on existing plantswithout a laboratory analysis. Okra, beans, cucum­bers or susceptible tomato varieties are good indicatorplants.

Educational programs conducted by the Texas Agricultural Extension Service serve people ofall ages regardless of socio-economic level, race,color, sex, religion or national origin.

Cooperative Extension Work in Agriculture and Home Economics, The Texas A&M University System and the United States Department ofAgriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8, 1914, as amended, and June 30, 1914.30M-10-78, Revision PP