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:

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 name^x	Weed Common name	Family	Root-Knot Nematodes^y
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

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 Web Site at http://edis.ifas.ufl.edu.

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.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, Dean.

Weed Hosts of Root-Knot Nematodes Common to Florida1