IRIS BORER (Macronoctua onusta).
Nearly always found with iris and
limited to this host. Eggs wintering on old iris leaves and other
debris hatch in late April or early May. Young larvae enter through pin-
point holes, and as the leaves grow up the caterpillars gnaw their way
down through soft leaf tissue toward the rhizome giving the leaf fans a
ragged and water-soaked appearance (Figure 15D). While in the leaves
the borers are white, fairly slender, about an inch long, but in July after
they have gouged out and gorged on the rhizomes they are nearly 2
inches long, repulsively fat and pinkish. The rhizomes may also be decay-
ing in a vile soft rot, for all too often the borers carry bacteria with them
as they feed. They come out of the rhizomes in August and form a
dark-brown pupa in the soil. Brownish, black-marked moths lay eggs in
September and October on or near the plants.
Control. Clean up all old leaves and debris around iris in the fall, a
week or two after hard frost. Spray or dust with DDT in spring, starting
when fans are about 6 inches high.
LILAC BORER (Podosesia syringae syringae).
Important on ash and moun-
tain-ash as well as lilac throughout the East and west to Colorado,
sometimes attacking privet and other ornamentals. Old lilac trunks are
almost always full of borer holes and protruding sawdust. The caterpillar
is white with a brown head, 11/2 inches long. The wasplike, clear-winged
moth emerges in June and July to lay eggs around rough scars on ash
limbs or at the base of lilac trunks. Partly grown larvae winter in tunnels
in the stem and start feeding again in the spring, there being only one
generation a year.
Control. Cut out old and dying or infested limbs. Spray trunks and
branches with DDT (or apply a strong solution with a paintbrush) about
the first of May before egg-laying. The treatment should be repeated once
or twice. Borers already at work can be killed in their tunnels with a wire
or by injecting lindane paste (Bor-tox) or carbon bisulfide.
LOCUST BORER (Megacyllene robiniae).
Very injurious to black locust in
street plantings and in forests, in fact the limiting factor in grow-
ing this tree. Infested young trees often break over a foot or so from the '
ground. Older trees are riddled with burrows with swollen areas and
irregularly scarred bark on the trunk. The grubs are cream-colored, about
an inch long when grown, legless and tapering, so they are rather club-
shaped. They pupate in cells in the wood, and the long-horned beetles,
black with conspicuous bright yellow markings, appear in late summer.
They lay eggs in bark cracks, and the young larvae work their way into
the inner bark before cold weather.