Crop Protection Guides
Onion Family Insect Pests
In This Guide
Where to look
Leaves are partially or completely consumed. Holes or
crescent-shaped areas in leaves are removed.
Chewing mouthparts. Armyworms, as the common name
implies, feed in groups. Caterpillars are dull green with many
light stripes along their backs and a broader stripe down each
of their sides. Their undersides are usually yellow. Adult moths
are grayish and can only be seen flying after dark.
Larva on onion leaf
Where to look
Feeding immatures will not be hidden, but are easily seen in groups on leaf surfaces.
Sometimes, larvae bore into tubular leaves and feed concealed inside. If feeding holes
are small, then look carefully at the leaves. The insects, in their early stages of
development, are small (about 5 mm long). Usually, you will find armyworms where
insect frass and new feeding damage can be seen.
Populations may develop continually throughout the year. Adult
moths lay their eggs in white to dull-white hair-covered clusters
on the leaves. When feeding is complete caterpillars pupate in
the soil. Populations can develop on some weed species. Beet
armyworm also feeds on tomato, soybean, groundnut, sugar
beet, and crucifers.
Larva on the surface of the
Spraying of chemical insecticides has been the major approach to combating
armyworm. But the pest is developing resistance to many chemicals. In response,
farmers sometimes mix several insecticides together in hope that one of them will be
effective. These strategies are not sustainable.
The use of alternative, biological control measures are very useful. Parasitic wasps and
nuclear polyhedrosis viruses (NPVs) that target armyworm are commercially available.
Strains of Bacillus thuringiensis (Bt) are u