Title: field study to determine potential host plants of lethal yellowing agent
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Title: field study to determine potential host plants of lethal yellowing agent
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4-i A


Field Study to Determine

Potential Host Plants

Of Lethal Yellowing Agent

F. W. Howard, J. R. Tilmant, D. G. Burch and D. Hall

Fort Lauderdale Research and Education Center
Institute of Food and Agricultural Sciences
University of Florida


Research Report FL-84-1


We wish to thank Jim DeFilippis, Glen Hutchinson, and Bryan
Steinberg for technical assistance. Mr. DeFilippis provided Fig. 2.
The cooperation of personnel of the National Park Service, Everglades
National Park, in assisting us to reach isolated localities and in
providing information is gratefully acknowledged.

Cover Photo. Coconut palms on Grassy Key affected by lethal yellowing disease.

A field study to determine potential host plants

of lethal yellowing agent.


F. W. Howard, Associate Professor of Entomology, University of
Florida, IFAS, Ft. Lauderdale Research and Education Center,
3205 S.W. College Avenue, Fort Lauderdale, Florida 33314

J. R. Tilmant, Biologist, National Park Service, Everglades
National Park, Homestead, Florida 33030

D. G. Burch, Extension Specialist, University of Florida, IFAS ,
Ft. Lauderdale Research and Education Center

D. Hall, Extension Botanist, IFAS, University of Florida,
Gainesville, Florida, 32611

Fort Lauderdale Research and Research Report FL-84-1
Education Center
Institute of Food and Agricultural Sciences
University of Florida
Fort Lauderdale, Florida 33314



A field study was conducted to attempt to single out plant spe-
cies that might possibly serve as symptomless hosts of the agent that
causes lethal yellowing (LY) of palms. Plants were identified in
small isolated areas in southern Florida affected by LY. Plant spe-
cies common to these areas, exclusive of maritime species, were exa-
mined in the field for evidence that they served as hosts for an
apparent LY vector, Myndus crudus Van Duzee. Ten species of plants
were common to the LY-affected areas examined. Six species were dico-
tyledonous and apparently not hosts of M. crudus. Four species were
graminaceous. Three of the latter (SteTotaphrum secundatum (Walt.) 0.
Kuntze, Cynodon dactylon (L.) Pers., and Cenchrus spp.) have been
reported as hosts of M. crudus. Evidence for particular species as
possible hosts of theLY agent are discussed.


Se condujo un studio de campo para seleccionar species de plan-
tas que posiblemente podrian servir como hospederas sin slntomas del
agent que causa el amarillamiento letal (AL) de las palmeras. Se
identificaron las plants en areas pequenas aisladas en el sur de
Florida. Las species de plants comunes en estas areas, exclusive de
species maritimas, se examinaron en el campo para evidencia que
sirvian como plants hospederas de un aparente vector de AL, Myndus
crudus Van Duzee. Diez species de plants eran comunes a las areas
examinadas. Seis species eran dicotiledoneas, y aparentamente no son
hospederas de M. crudus. Cuatro species eran graminaceas. Tres de
ellas (Stenota'phrum secundatum (Walt.) 0. Kuntze, Cynodon dactylon
(L.) Pers., y Cenchrus spp., se han registrado como hospederas de M.
crudus. Se discuten evidencia para species particulares como hospe-
deras del agent del AL.

Lethal yellowing (LY) is a mycoplasmalike organism
(MLO)-associated disease of coconut palms, Cocos nucifera L. (Beakbane
et al. 1972; Heinze et al. 1972; Hunt et al. 1974; Plavsic-Banjac et
aT.7T972; McCoy 197277 Tt least 30 aaii'Tonal species of palms are
aTfected by apparently the same disease (Thomas 1979, Thomas and
Norris 1980). Pandanus utilis Bory (Pandanaceae) is occasionally
affected by a lethal MLO-associated disease in Florida. This disease
may be identical to LY (Thomas and Donselman 1979). Otherwise there
is no evidence that plants other than palms serve as hosts of the LY

The disease can be held in remission by periodic antibiotic
injections (McCoy 1982) and this method has been recommended in
LY-affected areas of Florida in conjunction with replanting with spe-
cies and varieties of palms that are resistant to LY (Ennis 1982). A
cixiid planthopper, Myndus crudus Van Duzee, is an apparent vector
(Howard and Thomas 178T-,Ioward et al. 1983) but vector control has
not been developed sufficiently to control the disease (Howard and
McCoy 1980). Nymphs of M. crudus utilize various grass species as
hosts (Tsai and Kirsch 1778, Zenner de Polania and Lopez 1975) and the
adults go to palms of various species (Howard and Mead 1980).

In 1977 the International Council on Lethal Yellowing recommended
seven priority areas for research on the disease. One priority was
the identification of "alternate hosts", i.e., species of plants other
than palms that might carry the disease agent. The identification of
natural hosts other than palms might be useful in developing better
control measures. At present, the movement of LY susceptible palms is
restricted by quarantine regulations. If plant species other than
palms werefound to be hosts of the LY agent, quarantine measures
could be revised to include the regulation of movement of such plants.
Research on LY would be facilitated if a small herbaceous plant spe-
cies were found to serve as a host, because palms are generally more
difficult to propagate and maintain and have larger space requirements
than herbaceous plants. A dicotyledonous species would be par-
ticularly desirable as a host for research purposes, because the LY
agent could then be transmitted experimentally by grafting.
Monocotyledonous plants cannot be grafted.

Researchers and regulatory personnel consider a palm to be a host
of LY if it shows symptoms of that disease, and if the presence of MLO
in tissue samples is determined by electron microscopic (EM) examina-
tions (Thomas and Norris 1980). In field studies, diagnoses of LY are
usually based on symptoms alone, because it would not be practical to
screen large numbers of samples with an EM. The existence of symp-
tomless hosts is open to question. Carter (1964), in discussing the
difficulty of searching for "alternate" hosts, pointed out that about
125 species of flowering plants were found in a 6 ha. planting of
coconut palms in Jamaica. Thousands of native and exotic species grow
in LY-affected areas of Florida. Given this diversity, and since it
is an arduous process to prepare samples from a single plant and exa-
mine them by EM, it would be an extremely lengthy process to screen
these species for the presence of MLO. We took a different approach.

Generally fewer species of plants are found on small islands than
on large mainland areas. Plants found consistently on islands with
LY-infected palms could be considered as potential hosts of LY. We
felt, therefore that we could reduce the number of species to be con-
sidered as potential hosts of LY agent, by determining the plant spe-
cies in several of such areas affected by LY, and then seeking
evidence as to whether these species served as hosts of M. crudus.


Coconut plantings on the Florida Keys and in isolated inland
locations were examined for symptoms of LY. Three LY-affected
localities were selected for complete floiistic surveys: Ragged Key
#6, Flamingo, and Pigeon Key (Fig. 1).

West Palm Beach

Delray Bea

Ft. Lauderdale



ilged Key *6


tey West

Fig. 1. Southern Florida, showing localities examined in this study.

Ragged Key #6 is about 3 ha. in area, and about 0.5 km. north of
Sands Key, and 0.25 km. south of Ragged Key #5. We observed cases of
LY on Ragged Key #6 in December 1978. In April 1979 we counted 142
'Jamaica Tall' coconut palms on the island, nine of which had symp-
toms. More than 100 had died within a recent period, judging from the

number of freshly cut stumps. This high mortality rate is consistent
with that of LY, and cannot be attributed to other common mortality
factors of coconut palm in Florida. The nearest coconut plantings are
about 12 km. south on Elliott Key, about 13 km. west on the mainland,
and 8 km. north on Soldier Key. Coconuts on Elliott Key had LY symp-
toms in 1979. We visited Ragged Key #6 and identified all plant spe-
cies on the island in December and June 1978, and in April 1980.

Flamingo is a small resort settlement built around a ranger sta-
tion in Everglades National Park. There are about 5 ha. of maintained
lawns and plantings of shrubs and trees, including coconut palms.
Flamingo is isolated by Florida Bay to the south, and by wet prairies
and mangroves to the north. The nearest coconut palms are at East
Cape Sable, which is 17 km. to the west, Lower Matecumbe Key, which
is 38 km. to the south, and Pine Island, which is 44 km. to the
northeast. Of the 750 coconut palms present at Flamingo prior to the
introduction of LY abort 400 had been lost to this disease by the end
of 1979. (C. McClain, personal communication). LY was still active
in this locality in April 1980, at which time we identified all plant
species growing in the maintained area of Flamingo.

Pigeon Key is about 1.4 ha. in area (Figs. 2 & 3). The senior
author has visited this island at least once a year since 1976.
Symptoms of LY were first observed by the senior author in a coconut
palm on Pigeon Key in August 1981. Four of about 50 coconut palms
died, apparently from LY, during 1981. The next nearest LY-affected
coconut palms were at Marathon (Vaca Key), which is 3 km. from Pigeon
Key. This key is also the closest land area that could support
additional hosts of M. crudus. The vegetation of Pigeon Key was exa-
mined in February 19'92 to determine whether plant species common to
Ragged Key #6 and Flamingo also occurred there.
These 3 isolated localities are not typical of the urban areas of
Florida which have been severely affected by LY. The mangroves and
herbaceous salt marsh plants which are common to each of these loca-
lities are generally not found inland. To confirm this, all plants
were examined in 4 LY-affected areas of about 1/4 ha. each and at least
100 m from the shoreline in each of the following cities: Miami Beach
(May 1981), Delray Beach (May 1981) and Marathon (October 1981,
February 1982).

Palms were examined in each study area for the presence of
auchenorrhynchous insects, and these were identified.
Dicotyledonous plant species that were common to the LY-affected
localities were examined for M. crudus in the field at the Ft.
Lauderdale Agricultural ReseaFch and Lducation Center (AREC), in June
1981 and July 1982. This locality was chosen because it supports a
relatively high and continuous population of M. crudus. Plants of

1C. McClain, Superintendent, Everglades National Park, P.O. Box
279, Florida 33030


Fig. 2. Pigeon Key seen from the Overseas Highway that connects the
Florida Keys.

Fig. 3. A portion of Pigeon Key, showing 'Jamaica Tall' coconut palms,
mangroves and other maritime plants and grass lawn.


species with tap roots were sampled by examining stems and leaves,
then lifting them from the soil with a knife and examining the roots
and surrounding soil for M. crudus nymphs. Plants of species with
procumbent stems were sampledby -examining2the above-ground portions
and then digging up the plants from a 10 cm area and examining the
roots and surrounding soil. St. Augustine grass, Stenotaphrum
secundatum (Walt.) Kunze, was used as a standard of comparison, since
it has been reported as a highly favored host of M. crudus (Reinert
1980). Voucher insect and plant specimens were kTpt at the Ft.
Lauderdale AREC.


Ten plant species including 6 dicotyledenous and 4 graminaceous
species were common to all three isolated LY-affected localities
(Ragged Key #6, Flamingo, and Pigeon Key). These are listed below:

Spanish-needles, Bidens alba (L.) DC. L. (Asteraceae); pepper-
weed, Lepidium virginicum L.-(Brassicaceae); spurges: Chamaesyce
hirta (L.J Millsp. and C. hypericifolia (L.) Small, (Euphorbiaceae);
match-head, Phyla nodiflora (L.) Green (Lamiaceae); Southern sida,
Sida acuta Burm. f. (Malvaceae); sandspur, Cenchrus spp.; finger
grass, Chloris sp.; Bermuda grass, Cynodon dactylon (L.) Pers. and St.
Augustine grass, S. secundatum (Poaceae). All these species are known
to occur in LY-af0ected areas of the Caribbean region, including the
Bahamas, Cuba, Jamaica, Hispaniola and Quintana Roo (Mexico). This
list does not include plant species characteristic of salt marsh or
maritime habitats present in the three isolated localities, but not in
the urban areas examined in Miami Beach, Delray Beach and Marathon.
Such species are generally not present in LY-affected areas on the
mainland. An exception is seagrape, Coccoloba uvifera (L.) L
(Polygonaceae), a plant species native to maritime habitats which was
present in the three isolated localities and is a common ornamental
plant in inland areas of southeast Florida. In connection with
another study, (Howard, unpublished data), we have examined hundreds
of seagrape in several localities without observing M. crudus.
Myndus crudus adults were on coconut palms in all areas examined in
this study, and no other species of auchenorrhynchous insect was found
on palms. Myndus crudus was not found to be associated with the
following plant species examined in the field at Ft. Lauderdale AREC
(Species followed by the number examined): L. virginicum 35, S. acuta
200, P. nodiflora 100 (in June 1981); B. alFa 100, c. hypericTfoTT
118, 1. hirta 137 and P. nodiflora 100-(inTJuly 1987). Myndus crudus
nymphs were found assocTated with the roots of 16 of 100 samples o
St. Augustine grass examined during June 1981 and 46 of 100 samples
of St. Augustine grass examined during July 1982. We did not examine
other grass species listed for the presence of M. crudus nymphs, since
it has already been reported that M. crudus occurs on a wide variety
of grasses (Tsai and Kirsch 1978, Tenner de Polania and Lopez 1975).
Myndus crudus apparently prefers grasses and palms, which are
monocotyledonous plants (Tsai and Kirsch 1978, Zenner de Polania and
Lopez 1975) although Tsai and Kirsch reported that they observed M.
crudus nymphs feeding on the roots of Verbena scabra Vahl, a
dicotyledonous plant. It seems possible that T. crudus may feed on

other dicotyledonous plants, but this may be such a rare occurrence
that we did not detect it. Since there is no evidence for any other
insect species as a vector of LY, symptomless hosts of LY agent, if
they occur, are most likely to be St. Augustine grass, Bermuda grass,
sandspur, or finger grass, all of which were common to the three iso-
lated areas. St. Augustine grass is a highly favored host of M.
crudus (Eden-Green 1978, Reinert 1980) and the distribution ofLY in
Florida generally coincides with high incidence of this grass species
and of M. crudus (Howard 1980). Bermuda grass is apparently a less
favorabTe host (Reinert 1980). Sandspur was reported as a host of M.
pallidus (= M. crudus) in Colombia (Zenner de Polania and Lopez 197T).
Finger grass"has not been reported as a host, but this has not been
adequately tested. These four grass species are widely distributed in
warm countries and should be further studied as potential hosts of the
LY agent.

Literature Cited

Beakbane, A. B., Slater, C. H. W. and Posnette, A. F. 1972.
Mycoplasmas in the phloem of coconut, Cocos nucifera L., with
lethal yellowing disease. J. Hortic. Sci. 47:265.

Carter, W. 1964.
Present status of research on lethal yellowing disease of coconut
palm in Jamaica. FAO Plant Prot. Bull. 12:67-69.

Eden-Green, S. J. 1978.
Rearing and transmission techniques for Haplaxius sp., a suspected
vector of lethal yellowing disease of coconut palms in Jamaica.
Ann. Appl. Biol. 89:173-176.

Ennis, W. B. 1982.
Etat des recherches sur le jaunissement mortel et sur les maladies
similaires. Oleagineux 37:19-24.

Heinze, K., Petzold, H. and Marwitz, R. 1972.
Beitrag zur Atiologie der Todlichen Vergilbung der Kokospalme.
Phytopath. Z. 74:230-237.

Howard, F. W. 1980.
Population densities of Myndus crudus Van Duzee (Homoptera:
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in Florida. Principes 24:174-178.

Howard, F. W. and Mead, F. W. 1980.
A survey of Auchenorrhyncha (Insecta: Homoptera) associated with
palms in southern Florida. Trop. Agric. (Trinidad) 57:145-153.
Howard, F. W. and McCoy, R. E. 1980.
Reduction in spread of mycoplasmalike organism-associated lethal
decline of the palm, Veitchia merrillii, by the use of insec-
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Howard, F. W. and Thomas, D. L. 1980.
Transmission of palm lethal decline to Veitchia merrillii by a
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Hunt, P., Dabek, A. J. and Schuiling, M. 1974.
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Reinert, J. A. 1980.
Phenology and density of Haplaxius crudus (Homoptera: Cixiidae)
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Thomas, D. L. 1979.
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Thomas, D. L. and Donselman, H. M. 1979.
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Tsai, J. H. and Kirsch, 0. 1978.
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