WHITE-MARKED TUSSOCK MOTH (Hemerocampa leucostigmd).
This is a
pest of city shade trees, particularly sycamores, but also destructive
in some orchards, with foliage skeletonized and fruit scarred. The caterpillars are pale yellow with red head, a pencil tuft of black hair projecting
from either side of the head and from the tail, and four tufts of white
hairs along the back (Figure 40B). Female moths do not fly; they lay
eggs in masses, covered with hardened white froth, on trunks, branches,
and dead leaves.
Control. Egg masses can be daubed with creosote and trees sprayed with
lead arsenate or DDT. There are many parasites so that outbreaks are
seldom serious for more than a season or two at a time.
Nematodes are eel worms or roundworms; they live in moist soil water
or in decaying organic matter, and some become parasitic on plants. They
are so small they have to be seen under a microscope. They move through
the soil with a threshing motion but rarely make more than a few inches
a year, being spread to greater distances in irrigation water, on tools, or
with infested plants. In some nematodes both males and females are
wormlike, in others the female is pear-shaped and the male long and
narrow. Some live inside plant galls, and others live outside roots while
feeding on them, sucking out plant sap through a hollow spear.
CHRYSANTHEMUM LEAF NEMATODE (Aphelenchoides ritzema-bosi),
the worst problems in growing chrysanthemums in home gardens.
The nemas winter in the soil and in crown of old plants. If spring divisions are made by cutting up the old crown, then the nematodes go along,
but if new plants are made by rooting tip cuttings taken from apparently
healthy new shoots, then new plantings may be safe. Nematodes swim
up the stem in wet weather and into the leaves, causing a wedge-shaped
browning between the veins followed by the leaves turning entirely
brown and hanging down along the stem. Infestation starts with the
lowest leaves and progresses upward.
Control. Avoid overhead watering; use a mulch to keep nematodes
from being splashed up from soil in rains. Parathion gives good control
as a foliage spray, but for home gardeners treating soil with sodium
selenate is probably preferable, using it in a solution that will give exactly
54 gram of the chemical to a square foot of soil.
MEADOW NEMATODES (Pratylenchus spp.).
These are ecto-parasites feeding on and mutilating roots from the outside and not causing galls.
On boxwood they destroy much of the root system but often leave a
sort of witches' broom of fine feeding roots near the surface, put out by
the plant to compensate for the loss of other roots.