22May07

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22May07 TCE TAMU Most Not Wanted plants that
can be infected with the Pierces disease
bacterium in Texas Mark C. Black, Extension
Plant Pathologist, TCE TAMU, Uvalde, TX The
bacterium that causes Pierces disease (PD) of
grape, Xylella fastidiosa, infects several other
plants besides winegrape (Vitis vinifera). There
is diversity for host specificity and genetics
among X. fastidiosa populations cultured from
various hosts plants. However, presence of any
plant that harbors any strain of X. fastidiosa
may increase or indicate risk of PD in a nearby
vineyard. The glassy-winged sharpshooter, the
insect carrier of greatest concern, apparently
flies close to the ground and visits multiple
plant species over a large area for feeding,
reproduction, and winter survival. Great
distance between supplemental plant hosts and the
vineyard is detrimental for back-and-forth insect
movement, and is essential for reducing risk.
Riparian habitats (near water features) are
especially well suited for most of these host
plants. In Texas, symptoms and mortality
associated with X. fastidiosa are often most
intense in densely planted host plant species
that are not native to the region (southern U.S.
and northern Mexico) including winegrape,
oleander (Nerium oleander), and lavender
(Lavandula species). Other factors thought to
contribute to epidemics in highly susceptible
plants are high plant density, monoculture (one
plant species, typical of profitable plant
agricultural), and drought stress. This flyer
illustrates mostly native host plant species that
harbor X. fastidiosa, are widely distributed at
least locally, and occur in high populations at
rivers, streams, rights-of-way, vacant land, or
ornamental landscapes. Annuals include common
sunflower (Helianthus annuus), giant ragweed
blood ragweed(Ambrosia trifida var. texana),
hierba del marrano slim aster(Symphyotrichum
subulatum), seacoast sumpweed (Iva annua), and
narrowleaf sumpweed (Iva angustifolia). Of
three herbaceous perennial hosts, two occur
widely in central and southwest TX red-spike
mexican-hat (Ratibida columnifera) and western
ragweed perennial ragweed(Ambrosia
psilostachya). The third, widespread in west TX,
is Berlandier daisy chocolate flower(Berlandiera
lyrata). The two most common native grapes in
central and southwest TX, mustang grape (Vitis
mustangensis) and winter grape (V. cinerea var.
helleri), have only rarely been found infected
with X. fastidiosa, but we recommend they be
removed. One woody relative of grapes, heartleaf
ampelopsis (Ampelopsis cordata Vitaceae) was
infected at one site and had leaf scorch and vine
dieback. Other native woody host plants usually
have low incidence and minor symptoms in their
usual habitats. However, severe symptoms may
occur when these plants are used in landscaping
in dense plantings with severe environmental
stresses (poor soils, drought, heat, root damage,
etc.). These native woody host plants include
American sycamore (Platanus occidentalis), cedar
elm (Ulmus crassifolia), red mulberry (Morus
rubra), western soapberry (Sapindus saponaria
var. drummondii), redbud (Cercis canadensis), and
red oaks (Quercus buckleyi, Q. shumardii).
Ideally, vineyards should not be planted within
1 mile or more of these plants. Annual and
perennial vegetation near ground level where
glassy-winged sharpshooters concentrate is of
special concern. At existing vineyards, vigilant
efforts should be made to remove and control
these species by removal, mowing, or competition
with non-host plants. Vines with PD symptoms
should be immediately removed.
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Fig. 1. Pierces disease of winegrape in Texas
death of vine with fruit load (top)(note nearby
stand of trees in background) symptoms on young
vine (bottom left) and dead leaf margins (bottom
right).
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Fig. 2. Common sunflower (Helianthus annuus) in
(top to bottom, L to R) highway and railroad
rights-of-way, open flower, spent flower,
seedlings, and alternate leaf and branching habit.
Fig. 3. Giant ragweed blood ragweed(Ambrosia
trifida var. texana) in (top to bottom, L to R)
drainage ditch, near culverts, flowers, seedling,
and opposite leaf and branching habit.
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Hugh Wilson
Hugh Wilson
James Manhart
Fig. 5. Seacoast sumpweed (Iva annua) in moist
soils, seedling, opposite leaf and branch
pattern, and flowers.
Fig. 4. Hierba del marrano slim aster
(Symphyotrichum subulatum) in (top to bottom, L
to R) moist soil, growth habit, flowers, after
mowing, in bloom.