| SUCKING INSECTS OR MITES
This category includes those insects that
insert their mouthparts into a leaf or twig and suck the juices from the plant.
The tree's reaction is manifested by wilted or curled leaves, galls,
defoliation, branch tip dieback, or reduced growth. Determining the cause of
these symptoms usually depends on identifying the insect itself.
Mites are tiny 8-legged, spider-like
"bugs" closely related to insects. They have piercingsucking mouthparts and
cause damage resembling that produced by sucking insects. Expert identification
is often necessary to distinguish between the two.
VELVET GALL MITE,
Little is known about the
mites that occur on black walnut, but the velvet gall mite is common in some
areas. The mite itself is so small that it cannot be seen with the unaided
The velvet gall mite
causes a conspicuous velvety red growth up to an inch long on the leaf stem,
often causing the leaf to curl or twist over on itself. Galls may be numerous
on individual trees but they are considered to be harmless to the tree.
No control is
APHIDS OR PLANT LICE,
MONELLIA SP. AND MONELLIOPSIS SP.
of aphids are found on black walnut. They are a common, widely distributed
insect pest and occur wherever walnut is grown. They occur throughout the
growing season on the undersurface of walnut leaves.
Aphids are small, soft-bodied insects
with pear-shaped bodies; they may be brown, green, white, or purple in color.
Not all adult aphids have wings but when present the wings are transparent. The
nymphs resemble the adults in color and shape but are smaller in size.
Aphids suck the juices from leaves
and often deposit a sticky substance called "honey-dew" on the leaf surface.
Later, the surface of the leaves may turn black in response to a fungus that
grows on the honey-dew. This condition, known as "sooty-mold", may prevent
light from reaching the leaf surface and thus reduce photosynthesis.
|Aphids on black walnut
Normally, aphids are sparse on black
walnut and therefore probably cause little damage. However, if conditions
permit, populations can become large. Symptoms of aphid activity include
curling of leaves, yellowing, defoliation, reduction of growth, and, in extreme
cases, branch dieback.
No control is
recommended unless serious damage occurs. Then consult your local county
extension agent for chemical controls.
The periodical cicada is also known as the
13year (Magicicada tredecassini Alex. & Moore) or the 17-year (M.
septendecim (L.)) locust, appearing in great numbers every 13 years in the
South and every 17 years in the North. Periodical cicadas are widely
distributed throughout eastern United States.
Adult cicadas are large, dark,
heavy-bodied insects with membranous wings and red eyes. The females possess a
strong ovipositor. Adult cicadas can reach 1-1/2 inches in length. Nymphs live
in the soil, feeding on plant roots, and so are rarely seen. Adult male cicadas
produce a characteristic sound by vibrating their wings against their body.
Injury to black walnut
trees is caused by the adult female as she uses her ovipositor to make jagged
slits in the bark and wood of twigs and small branches. Shredded wood fibers
may be seen protruding from the slits. Affected twigs and branches are weakened
and commonly break off in strong winds. Oviposition scars may be visible for
several years after the injury was made.
No controls are
Several species of plant hoppers have been
found on black walnut, the most common of which are Anormenis
septentrionalis (Spinola) and Metcalfa pruinosa (Say).
The nymphs of both species are similar in
color and size. They resemble small fluffy masses of cotton because of white
waxy secretions they deposit around themselves and on the plant. Adults of
Metcalfa pruinosa are dark blue-black in color, sometimes with a
white,powdery substance obscuring the color. Anormenis septentrionalis
adults are green to yellow-green. Both species are approximately 1/4 inch long
and they hold their wings flat against the sides of their bodies. Plant hoppers
are noted for their ability to jump when disturbed.
Adults and nymphs are
sucking insects, feeding on sap taken from leaves and stems of smaller twigs.
Feeding damage is considered insignificant. The female adult, however, may
cause the tips of small twigs to die when she deposits her eggs in zipper-like
slits beneath the bark.
Control is usually not
ENCHENOPA BINOTATA (SAY)
The 2-marked treehopper is a
small, darkbrown insect with two yellow spots on the center of its back. It has
a thorn-like projection over the head and jumps when disturbed. Adults are
approximately 1/4 inch long. The nymphs are black with white markings and often
have spinelike structures extending from their abdomens. Treehoppers are widely
distributed throughout eastern United States.
Both adults and nymphs
suck sap from walnut leaves. Often they can be seen feeding on the lower leaf
surface or on the leaf rachis. Although they may be abundant within a
plantation, their feeding habits do not appear to cause serious damage.
However, female adults can damage twigs when they deposit eggs into small slits
made by their ovipositors. After the eggs are laid the female covers them with
a white frothy "plug" that later turns brown. After the eggs hatch, the slits
remain evident as scars for several years. Treehoppers are present on walnut
trees throughout the growing season.
Control is usually
WALNUT LACE BUG,
The walnut lace
bug feeds almost exclusively on black walnut and is found throughout the range
of black walnut.
It is so named because of the
adult's lacy wingcovers. The head is covered with a lace-like, arching hood.
Adults are about 1/5 inch long and have transparent white wingcovers with dark
bodies. The nymphs are much smaller, dark brown in color, and oval-shaped.
Both adults and
nymphs are found together on the lower surfaces of walnut leaflets where they
suck the sap from the leaves. More than 100 nymphs and adults may be present at
one time on one leaflet. Areas where they have fed are easily recognized
because of cast skins, excrement, and dark, discolored patches of leaf. The
upper leaf surface is stippled with tiny white spots that give the upper leaf
surface a whitish appearance. Leaves of heavily infested trees may turn brown
and fall off.
local service forester or county extension agent for the recommended control