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Publication #ENY-060

Weed Hosts of Root-Knot Nematodes Common to Florida1

Jim Rich, Janete Brito, Jay Ferrell, and Ramandeep Kaur2

Root-knot nematodes (Meloidogyne spp.) are the most widespread and damaging of the plant-parasitic nematodes found in Florida, and they survive and even thrive on weeds. To date, about 97 root-knot nematode species have been described, but within the genus, M. arenaria, M. incognita, and M. javanica (peanut, southern and Javanese root-knot nematodes, respectively) represent 95% of all root-knot nematode problems in Florida. Other root-knot nematodes found causing problems in specific crops in the state include M. graminis, M. mayaguensis and M. partityla (grass, guava and pecan root-knot nematodes, respectively). Weeds and nematodes are widely present in Florida agro-ecosystems, and the interaction of these primary pests can magnify problems compared to each acting alone. Because weeds are widely present and many are good hosts of root-knot nematodes, weed control is an excellent first step in reducing root-knot nematode damage in Florida agriculture.

To determine the status of weeds as hosts of root-knot nematodes, greenhouse and field evaluations were used to measure nematode reproduction of individual nematode and weed combinations. For practical field observations, however, galling on plant roots most times indicates nematode reproduction on a weed or crop plant and generally the greater degree of galling, the greater root-knot nematode reproduction on the plant (Figure 1).

Figure 1. 

Root galling (knots) on Amaranth infected with Guava root-knot nematode (Meloidogyne mayaguensis).


[Click thumbnail to enlarge.]

Importance of Weeds as Nematode Hosts

The host status and degree of nematode reproduction on weeds is a major concern in developing and implementing integrated nematode management programs because weeds are almost universally present during crop growth and afterwards in fallow periods. This is contrary to modern perceptions of many professionals who now consider that weeds are not major constraints in agricultural production due to the excellent control provided by herbicides. However, weed control is often conducted relative to weed populations and threshold levels established for weed/crop competition. If weed populations are relatively low or grow only late in the season, it may be viewed as unprofitable to perform weed control, regardless of whether these weeds are hosts of plant-parasitic nematodes. Additionally, most row crop and vegetable acreage remains fallow for long periods of the year, and weeds grow in abundance during these periods. These fallow periods may last from 3-6 months and are natural in most crop production cycles. For example, in north Florida thousands of acres of cotton and peanut are harvested in September and October each year, and the land may not be used again for crop production for over 6 months until planting commences the following May.

Figure 2. 

Unless controlled during the off-season, weeds may maintain or increase nematode populations.


[Click thumbnail to enlarge.]

Nematode reproduction on weeds may seem to be a simple problem to solve – simply control weeds, particularly in the off-cropping season. However, this could lead to increased grower cost, greater soil erosion potential, less nutrient recycling, and lower soil organic matter levels. Some options to reduce these negative aspects would include selectively eliminating major weed hosts with herbicides (mostly broadleaf weeds), encouraging the growth of non-host weeds (mostly grassy weeds), or planting cover crops that suppress weed populations. It is important to emphasize that without a strong weed management program both in-season and off-season, the benefits of crop rotation for nematode management can be quickly annulled by weed hosts of plant-parasitic nematodes.

Weeds as Monitoring Tools

Knowledge about weeds as hosts of root-knot nematodes, particularly weeds known to be highly symptomatic hosts, makes it possible to use existing weeds to monitor fields for those nematodes. This is especially important when laboratory assays are impractical or when more data points on nematode infestation are needed than can be derived by laboratory soil assay alone. For instance, the citron melon has been used to monitor the peanut root-knot nematode in north Florida fields and several leguminous weed species were used to index a root-knot nematode infestation in fields to be planted to cantaloupes.

Conclusions

Information presented in Table 1 shows only those weed species found to be hosts to one or more common root-knot nematodes found in Florida. However, it is important to also remember that some weeds are NOT hosts of plant-parasitic nematodes, a fact that may be useful in management programs. For example, UF/IFAS Nematologist Dr. Harlan Rhoades found that a summer cover crop of hairy indigo (Indigofera hirsuta) was a non-host to the southern and Javanese root-knot nematodes as well as the sting nematode (Belonolaimus longicaudatus). In field experiments, hairy indigo rotation was very effective for control of those nematode species in subsequent vegetable crop production.

Overall, information on the host range of root-knot nematodes on weeds is incomplete and sometimes contradictory, and many additional studies are necessary to adequately describe this subject. For example, a recent review article stated that weed hosts had only been studied for 14 of the 97 species of root-knot nematodes known worldwide (1). In addition, there are 3479 recognized weed species in the Weed Science Society of America database, suggesting that much is left to be known about weed hosts to root-knot nematodes.

Lastly, weeds present in agricultural fields any time during the year may compromise carefully documented and effective rotation systems for nematode management. Thus, weed management both within and after the normal cropping cycle is an overlooked yet critical component of nematode management systems.

Literature

A more complete listing of weed hosts of root-knot nematodes worldwide may be found in:

  1. Rich, J. R, J. A. Brito, R. Kaur, and J. A. Ferrell. 2009. Weed species as hosts of Meloidogyne: A review. Nematropica 39:157-185.

Tables

Table 1. 

List of selected Florida weeds, their common names and botanical families occurring as hosts of root-knot nematodes commonly found in Florida.

Scientific namex

Weed Common name

Family

Root-Knot Nematodesy

Abutilon theophrasti

Velvet leaf

Malvaceae

Ma, Mi, Mj, Mm

Acalypha australis

Australian acalypha

Euphorbiaceae

Mi

A. setosa

Copperleaf

Euphorbiaceae

Ma, Mi

Achillea millefolium

Common yarrow

Asteraceae

M. sp.z

Achyranthes aspera

Prickly chaff-flower

Amaranthaceae

Mi

Aerva javanica

Kapok bush

Amaranthaceae

Mi

Ageratum conyzoides

Goat weed

Asteraceae

M. sp.,

Alternanthera sessilis

Sessile joyweed

Amaranthaceae

Mi

Amaranthus graecizans

Tumbleweed

Amaranthaceae

Mi, M. sp.

A. hybridus

Smooth pigweed

Amaranthaceae

Ma, Mi, Mj

A. palmeri

Palmer amaranth

Amaranthaceae

Ma, Mi

A. retroflexus

Redroot amaranth,

Amaranthaceae

Ma, Mi, Mj, Mm

A. spinosus

Spiny amaranth

Amaranthaceae

Ma, Mi, Mj, Mm

A. viridis

Slender amaranth

Amaranthaceae

Mi

Ambrosia artemisiifolia

Common ragweed

Asteraceae

Ma, Mi

Avena spp.

Wild Oats

Poaceae

M. sp.

Axonopus affinis

Carpetgrass

Poaceae

Mi

Bidens alba

Common beggartick

Asteraceae

Mi

B. frondosa

Devils'beggar tick

Asteraceae

Mi

B. pilosa

Hairy begger tick

Asteraceae

M. sp., Mj, Mm

Bromus secalinus

Cheat

Poaceae

Mi

Capsella bursa-pastoris

Shepherd's purse

Brassicacea

M. sp.

Celosia argentea

Celosia

Amaranthaceae

Mi

Cenchrus spinifex

Field sandbur

Poaceae

Ma, Mi

Cerastium fontanum ssp. vulgare

Mouse ear chickweed

Caryophyllaceae

Mi

Chamaesyce hirta

Garden spurge

Euphorbiaceae

Mi

C. maculate

Spotted spurge

Euphorbiaceae

Ma, Mi

C. prostrata

Ground spurge

Euphorbiaceae

M. sp., Mm

Chenopodium album

Common lambs-quarters

Chenopodiaceae

Ma, Mi

C. murale

Nettle-leaf goosefoot

Chenopodiaceae

Mi

Citrullus lanatus

citronmelon

Cucurbitaceae

Ma

Cleome viscosa

Jasmin del rio

Capparaceae

Mi

Cnidosculus stimulosus

Spurge nettle

Euphorbiaceae

Ma, Mm

Commelina benghalensis

Benghal dayflower

Commelinaceae

M. sp.

C. communis

Asiatic dayflower

Commelinaceae

M. sp.

C. diffusa

Spreading dayflower

Commelinaceae

M. sp.

Conyza albida

Fleabane

Asteraceae

M. sp.

Crotalaria spectablis

Showy crotalaria

Fabaceae

Ma, Mi

Cynodon dactylon

Bermudagrass

Poaceae

Ma, Mi

Cyperus sp.

Sedge

Cyperaceae

Mj

C. difformis

Smallflower sedge

Cyperaceae

M. sp.

C. esculentus

Yellow nutsedge

Cyperaceae

Mi, Ma

C. rotundus

Purple nutsedge

Cyperaceae

Ma, Mi

C. sanguinolentus

Bloodscale sedge

Cyperaceae

M. sp.

Dactyloctenium aegyptium

Crowfootgrass

Poaceae

M. sp.

Datura inoxia

Sacred dactura

Solanaceae

Mi

D. stramonium

Jimsonweed

Solanaceae

Ma, Mi

Daucus carota

Wild carrot

Umbelliferae

Mi, M. sp.

Desmodium sp.

Beggarweed

Fabaceae

Mi

Dichondra repens

Dichondra

Convolvulaceae

Ma, Mi, Mj, Mm

Digitaria horizontalis

Jamaican crabgrass

Poaceae

Mi

D. sanguinalis

Large crabgrass

Poaceae

Ma

Echinochloa colona

Jungle-rice

Poaceae

M. sp.

Echinochloa crus-galli

Barnyard-grass

Poaceae

Ma, Mi

E. muricata

Rough barnyard-grass

Poaceae

Ma

E. prostrata

Eclipta

Compositae

Mm

Eleusine indica

Goosegrass

Poaceae

Ma, Mi

Elymus repens

Quackgrass

Poaceae

M. sp.

Emilia sonchifolia

Red tassle-flower

Asteraceae

Mi, Mm

Erechtites hieracifolia

American burnweed

Asteraceae

Mi, Mj

Euphorbia heterophylla

Wild poinsettia

Euphorbiaceae

Mj

E. hirta

Asthma plant

Euphorbiaceae

Mi

E. tirucalli

Indiantree

Euphorbiaceae

Mm

Fatoua villosa

Mulberryweed

Moraceae

Mm

Hydrocotyle bonariensis

Pennywort

Apiaceae

Mm

Indigofera sp.

Indigo

Fabaceae

Mj

Ipomoea grandifolia

Morning-glory

Convolvulaceae

M. sp.

I. hederacea

Ivyleaf morning-glory

Convolvulaceae

Ma, Mi

I. quamoclit

Cypressvine morning-glory

Convolvulaceae

M. sp.

I. triloba

Three-lobed morning-glory

Convolvulaceae

Ma, Mi, Mj, Mm

I. tricolor

Multicolored morning-glory

Convolvulaceae

M. sp., Mm

Jacquemontia tamnifolia

Small flower morning-glory

Convolvulaceae

Ma, Mi

Lactuca saligna

Willowleaf, lettuce

Asteraceae

Mi

Leontodon hispidus

Bristly hawkbit

Asteraceae

Ma, Mm

Lucas aspera

Thumba plant

 

Mi

Macroptilium lathyroides

Phasey bean

Fabaceae

Ma

Malva neglecta

Common mallow

Malvaceae

Mi

Medicago lupulina

Black medic

Fabaceae

Mi

Melilotus alba

White sweetclover

Fabaceae

Mi

Melilotus indica

Sourclover

Fabaceae

M. sp.

Mikania micrantha

Mile-a-minute

Asteraceae

M. sp.

Mimosa pudica

Sensitive Plant

Fabaceae

M. sp.

Mollugo sp.

Carpetweed

Aizoaceaee

Mi

Morella faya

fayatree

Myricaceae

M. sp.

Nasturtium officinalis

Watercress

Cruciferae

M. sp.

Oenothera biennis

Common evening- primrose

Onagraceae

Ma

Oxalis corniculata

Creeping woodsorrel

Oxalidaceae

M. sp.

Panicum miliaceum

Wildproso millet

Poaceae

Mi

P. repens

Torpedograss

Poaceae

M. sp.

Paspalum notatum

Bahia-grass

Poaceae

Ma, Mi

Passiflora mucronata

Passion flower

Passifloraceae

Mm

Pennisetum purpureum

Napiergrass

Poaceae

Mi

Peperomia pellucida

Shiny bush, pepper elder

Piperaceae

M. sp.

Physalis spp.

Ground cherry

Solanaceae

Ma, Mi, Mj

Physalis angulata

Cutleaf groundcherry

Solanaceae

Ma

Phytolacca americana

American pokeweed

Phytolaccaceae

Ma, Mi, Mj, Mm

Plantago major

Broadleaf plantain

Plantaginaceae

M. sp.

Poa annua

Annual bluegrass

Poaceae

M. sp.

Polygonum persicaria

Ladysthumb

Polygonaceae

Mi

Phragmites communis

Common reed

Poaceae

M. sp.

Portulaca grandiflora

Showy purslane

Portulacaceae

Mi

P. oleracea

Common purslane

Portulacaceae

Ma, Mi, Mj, Mm

Raphanus raphanistrum

Wild radish

Brassicaceae

M. sp.

Richardia brasiliensis

Brazil pusley

Rubiaceae

M. sp.

R. scabra

Florida pusley

Rubiaceae

Mi

Rumex acetosella

Red sorrel

Polygonaceae

Ma, Mi

R. crispus

Curly dock

Polygonaceae

Mi, Ma

Senna alata

Emperor's candlesticks

Fabaceae

Mm

S. obtusifolia

Sickle pod

Fabaceae

Ma, Mi, Mj, Mm

S. occidentalis

Coffee senna

Fabaceae

Mi, Mj, Mm

Sesbania sp.

Sesban or sesbania

Fabaceae

Mi, Mj

S. aculeate

Prickly sesbania

Fabaceae

Mj

Setaria pumila

Yellow foxtail

Poaceae

Ma

S. viridis

Green foxtail

Poaceae

Ma, Mi

Sida acuta

Southern sida

Malvaceae

Mi

S. spinosa

Prickly sida

Malvaceae

Ma, Mi

Solanum sp.

Nightshade

Solanaceae

Ma, Mi

Solanum americanum

American black nightshade

Solanaceae

Mi, Mj, Mm

S. nigrum

Black nightshade

Solanaceae

Mi, Mj, M. sp.

S. torvum

Turkeyberry

Solanaceae

M. sp., Ma

S. viarum

Tropical soda apple

Solanaceae

Ma

Sonchus oleraceus

Common sowthistle

Asteraceae

Mi, Mj

Sorghum bicolor ssp. arundinaceum

Wild sorghum

Poaceae

M. sp.

S. halepense

Johnsongrass

Poaceae

M sp.

Spergula arvensis

Corn spurry

Caryophyllaceae

M. sp.

Spermacoce confusa

Button weed

Rubiaceae

M. sp.

Stellaria media

Common chickweed

Caryophyllaceae

Mi,

Talinum triangulare

Waterleaf

Portulacaceae

Mm

Tamarix gallica

Saltcedar

Tamaricaceae

Mj

Taraxacum officinale

Common dandelion

Asteraceae

Ma, Mi

Thlaspi arvense

Field pennycress

Brassicacea

Mi

Trifolium repens

White clover

Fabaceae

Mi

Urena lobata

Cadillo

Malvaceae

Mi, M. sp.

Urochloa ramosa

Browntop millet

Poaceae

M. sp.

Verbena officinalis

Vervain

Verbenaceae

Mi

Veronica spp.

Speedwell

Scrophulariaceae

M. sp.

Vicia villosa

Hairy vetch

Fabaceae

Ma, Mi

Withania somnifera

Ashwagandha

Solanaceae

Mi

Xanthium strumarium

Common cocklebur

Asteraceae

Ma, Mi

x Many scientific names of weeds and even family names have changed over the past few years; weed names presented herein are those used by the Weed Science Society of America (http://www.wssa.net/Weeds/ID/WeedNames/namesearch.php).

yMa = Meloidogyne arenaria - Peanut root-knot nematode; Mi = M. incognita – Southern root-knot nematode; Mj = M. javanica – Javanese root-knot nematode; Mm - M. mayaguensis – Guava root-knot nematode.

z M. sp. = Species of root-knot nematode not identified.

Footnotes

1.

This document is ENY-060, one of a series of the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date April 1, 2010. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Jimmy R. Rich, professor, North Florida REC, Institute of Food and Agricultural Sciences, University of Florida, Quincy, FL 32351; Janete Brito, nematologist, FDACS Division of Plant Industry, and Courtesy Faculty, Entomology and Nematology Department, University of Florida, Gainesville, FL 32611; Jason Ferrell, associate professor, Agronomy Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611; and Ramandeep Kaur, research associate, Department of Plant Pathology, Louisiana State University Agricultrual Center, Baton Rouge, LA 70803.


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