APHIDS OR PLANT LICE,
MONELLIA SP. AND MONELLIOPSIS SP.

Description
    Several species 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.
aphid
Injury

Aphids on black walnut
Aphids on black walnut
    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.

    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.

Control
    No control is recommended unless serious damage occurs. Then consult your local county extension agent for chemical controls.

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