Economic damage to asparagus:
| Asparagus Beetle | ||
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larva of asparagus beetle |
adult asparagus beetle |
eggs |
There are two species of beetles
that attack and cause economic damage to asparagus. They are the common asparagus beetle,
Crioceris asparagi (Linnaeus), and the spotted asparagus beetle, Crioceris
duodecimpunctata (Linnaeus). The common asparagus beetle is the more widespread of the two
species.
Common Beetle
Description:
The common asparagus beetle is 1/4 inch in length,
has a bluish black head, legs and antennae tinged with green, reddish thorax and the wing
covers are marked by yellowish patches and reddish borders. The larva or grub of this
beetle is dark gray to olive green with black legs and head.
Injury:
Both the larvae and the adults of the common
asparagus beetle damage the asparagus plants. The overwintered adults emerge and begin to
feed on the tender growing tips of newly sprouted asparagus. They eat out holes and cause
a brownish discoloration of the tissue. The grubs will feed on the tender young tips and
on foliage. The plant growth is seriously reduced and proper root development prevented
causing a decrease in the size and quality of the crop.
Life History:
Adult beetles overwinter in sheltered places such
as piles of rubbish and heaps of old asparagus tops. They emerge from their shelter when
the new shoots come up and begin feeding on the tender tips. They soon lay eggs on the
young shoots. The eggs are elongate, oval, and deposited either singly or in rows of two
to eight. Later in the season the eggs are laid on leaves and flower stems.
The eggs hatch in 3 to 8 days and the grubs begin feeding on the tender tips. When the
grubs mature, they drop to the ground and construct a small earthen cell where they
transform into pale yellowish pupae. The adult beetles emerge from the pupae. There may be
two or more generations per year depending on the climate.
Spoted Asparagus Beetle
Description:
The spotted asparagus beetle is slightly larger and
more robust than the common asparagus beetle. The adults are reddish-orange in color with
black antennae, eyes and underside of thorax. Each wing cover has six distinct black
spots.
Injury:
This beetle is most injurious in the early season
when the adults attack the growing tips and sometimes eat the buds of newly sprouted
asparagus. The beetles also feed on foliage eating out irregular areas. The larvae cause
little damage because they feed inside the berries.
Life History:
The adult beetles overwinter in piles of debris.
They leave their winter quarters about one week later than the common asparagus beetles
and begin to feed on the tender young shoots. They do not deposit eggs until the plant
begins to blossom, about three weeks after they've emerged. The egg is deposited singly on
plants, usually those bearing fruit. The egg is 1/25 inch in length, olive brown, and
attached to the leaf by one side. The grubs hatch in 7 to 12 days and are yellowish-orange
in color with a black head and legs. The larva finds a berry and enters it at the blossom
end. Inside the berry it feeds on the seeds and it may attack 3 or 4 berries before it is
mature. When fully grown, it drops to the ground by a silken thread and spins a cocoon
just under the soil surface.
Management:
Cutting the shoots very clean and just below ground
level every day or two during the cutting season will tend to remove the eggs of the
common asparagus beetle before the larvae can establish themselves in a home garden patch.
In small gardens gathering and destroying of the asparagus berries will help to give
control of the spotted asparagus beetle.
Either the insecticide carbaryl (Sevin), malathion, methoxychlor or rotenone may be used
for control. Apply the insecticide when the beetles first appear. Apply as frequently as
needed but do not repeat applications within 3 days. Be sure to check the number of days
you have to wait to harvest (=Days to Harvest) before applying any pesticide to edible
crops.
