Aphids
Aphids are
soft-bodied insects that feed on plant juices. They are usually
found on new growth and on the undersides of leaves. They excrete
excess liquid as honeydew, a sweet substance that forms a sticky
coating on leaves and may fall onto sidewalks and cars. Ants are
attracted to honeydew and sometimes tend aphid colonies in order
to have a supply of honeydew. Some aphids can spread plant diseases.
Aphids have
an interesting life cycle that allows them to rapidly increase their
numbers. Many species have both a winged and a wingless form. Most
species feed on one kind of plant or on several closely related
plants. So aphids on your nasturtiums will not necessarily spread
to your pea patch.
One of the
first pests to arrive in spring, aphids are not usually noticed
until the population has built up. Most plants can tolerate modest
aphid infestations; aphids are always present at some level in the
yard and garden. They can usually be kept at tolerable levels with
physical and biological controls.
Chemical
insecticides are often ineffective for managing aphid infestations
because they temporarily reduce aphid numbers while killing off
the natural enemies such as ladybugs and lacewings.
Prevention
Avoid growing
plant varieties that attract aphids. Maintain healthy plants. Stressed
plants are more susceptible to infestation. Use floating row covers
on garden beds to exclude insects, yet allow air, light and moisture
to penetrate. Row covers are available at garden stores.
Biological
Control
Natural
enemies of aphids include lady beetles, lacewings, spiders, various
flies, midges and small wasps. Usually they can keep aphids under
control, but there may be times, especially early in the gardening
season, when aphids increase faster than the predatory insects.
Some garden stores and catalogs sell lady bugs, but in most cases
they will not stay in your yard when released. Certain plants are
reputed to attract beneficial insects. Examples are parsley, coriander,
fennel, yarrow, artemisia, and asters.
Physical
Methods
Wash aphids
off plants with a strong stream of water. This may have to be repeated
every 3-4 days. Or try soapy water to wash aphids off. (Test your
soap solution on a small portion of the plant first.) If the infestation
is limited you might clip off the infested leaves or stems and dispose
of clippings in soapy water to kill the aphids. Keep soil nitrogen
levels moderate. Aphids are more likely to infest plants that have
been fed with highly soluble nitrogen fertilizer. Use compost or
a slower-acting fertilizer instead.
Least
Toxic Chemicals
Try a commercially
available insecticidal soap such as Safer's. Another product used
by organic growers is neem oil, which contains the active ingredient
azadirachtin. Neem spray smothers aphids and other pests and prevents
their eggs from hatching. Neem oil can kill a wide variety of insects,
so use it with caution and only if other control methods fail. If
you use it on edible crops, be sure to wash them before use with
a soap approved for use as a food wash.
