Strange and Unusual Bug Symptoms-
Galls, Twig Girdler, Spittlebug and Slime Mold
One of the most fascinating, and sometimes
disturbing, phenomena in the world of plant problems is the
gall. Gall formations have been observed in this area on red
oak (cottony gall and apple gall), live oak (gouty oak gall),
hackberry (nipple gall), pecan (phylloxera) and live oak (red
"berry galls" on the bottom side of leaves). We
might as well "enjoy" them. Spraying after you see
galls won't make them disappear. They're part of the leaf,
not the insect that causes them. Preventive spraying, repeated
several times earlier in the year, possibly could have reduced
the population of these tiny, wasp?like insects that cause
this growth. Despite their undesirable appearance, they don't
kill or even maim trees.
Galls are caused by many species of mites and
insects that feed and grow completely protected inside the
gall structure. The most prominent family of insects causing
galls is the Cynipidae, or the Gall?fly family. Galls made
by mites and aphids have openings from which the young can
escape. But with gall?fly, the gall is completely enclosed,
and a hole must be made by the insect in order to emerge.
Each species of gall insect infests a special
part of one or more particular species of plant, and the gall
produced by each species of insect is of a definite form.
They develop under some stimulus from the insects that lay
their eggs in the plant tissue. The nature of the stimulus
is not yet understood, but is dependent on the insect's acute
chemical sense that enables it to recognize by smell and taste
many essential oils and other substances in particular plants.
One can speculate that the insect secretes some growth regulator
that causes the nucleic acids in the plant tissue to program
the abnormal development. In the case of the gall?fly, the
gall forms after the larvae develop from eggs.
Actually, most gall formations are not injurious
to the plant. This is fortunate because control is practically
impossible when the insect is protected inside the plant tissue.
Effective control-spraying could be made at or before egg
laying time. This would be a preventive spray with an insecticide.
The most logical time would be when the new leaves first emerge
from the bud in the spring. However, it is difficult to decide
whether or not the expense of spraying is warranted. This
remains an individual decision.
As with many other plant problems, it is again
important to recognize the malady, understand the probable
extent of its damage, and realize that once the gall appears,
it is too late to spray.
Relevant to our live oak galls and live oak
twig blight, a preventive spray at bud break in the spring
with a fungicide (Kocide) and insecticide?miticide (Orthenex
or Diazinon) should prove to be a rewarding practice-at least
from an aesthetic point of view. With this in mind, the gardening
calendar should be marked now for a preventive spray at bud
break time next spring if you have had reoccurring instances
with these problems.
The twig girdler is also a concern to some
folks. Fallen branches, usually not over ½- inch in
diameter, are found neatly girdled as if by a whittling knife.
But it's no man or boy sitting up in that pecan, elm, ash,
mimosa, poplar, or several other varieties of trees. It is
a beetle about 1-inch long. Their antennae are as long as
their body. They have very strong mandibles that they use
to cut through twigs and branches. The females do this pruning,
sometimes spending 2 days to girdle the stem as they lay their
eggs inside the portion of the severed limb. Twigs begin to
fall to the ground usually in late summer. This grayish, ugly
insect causes little damage generally, but when females are
numerous, excessive girdling may occur.
Chemical controls are effective when timed
properly. Sprays containing malathion, sevin or other general
purpose sprays that are currently available, should be applied
to trees when the first damage is detected. Three applications
of spray at 2?week intervals are usually necessary to prevent
damage. Infestations can also be reduced by gathering and
burning all of the fallen twigs so that the eggs and larvae
of "Girdling Gertie" are destroyed.
The spittlebug found on the twigs and branches
of pecan trees or grape vines also causes a great deal of
concern. The spittlebug appears around the buds and tender
shoots as masses of frothy, white foam that looks like a mass
of human spit. Often this is mistaken for a fungus or disease.
Actually, inside this mass of white foam is a tiny light green
insect known as the spittlebug. The frothy mass produced by
the spittlebug presumably protects the young insect from other
parasitic-type insects, and maintains an artificial high humidity
required for the insect's development.
The adult resembles a leafhopper and flies
actively during the summer. The spittlebug has not been known
to cause any significant injury on pecans or grapes in Texas,
and control measures are not generally recommended from the
Finally, the last but certainly not the least,
abnormality of concern is a group of fungi known as slime
molds which often covers grass with a dusty bluish?gray, black
or yellow mass. Slime molds are not parasitic on grass, but
they are unsightly. They feed on dead organic matter. The
most damage they do to grass plants is to shade and discolor
Slime molds occur usually after heavy rains
or watering, but will disappear as soon as the turf grass
dries out. The large masses of spores may be a nuisance because
of the abundance of dark spores that rub off on shoes and
clothing. They can be broken up readily by sweeping the lawn
with a broom, or spraying with a strong stream of water.
So, if you see some of these "strange"
plant symptoms in your landscape, fear not. What you see has
happened before and will, in all probability, happen again.
It just so happens that this time, it is happening to you!