Asparagus (Asparagus)
Plant Health Problems
Diseases caused by Fungi:
Fusarium crown and root rot, Fusarium oxysporum f.
sp. asparagi and Fusarium proliferatum.
The disease can appear during the summer after the ferns have
developed. Plants become stunted and individual stems will
exhibit a lemon-yellow color in the fern and then wilt and die
after a few days. Entire crowns can succumb and leave large
misses in the row. The fungi are soilborne and seedborne.
Although all cultivars can become diseased, the all-male hybrids
show considerable vigor and tolerance to the disease. The disease
can be suppressed by improving soil pH (optimum pH = 7.0),
controlling weeds and insects, and irrigating during periods of
drought. Older fields in Connecticut have responded to a dressing
of NaCl (2 lbs./20 ft.) applied once in the spring. New plantings
should use the vigorous all-male hybrid cultivars. Pesticides are
not effective for control of this disease.
Rust, Puccinia asparagi.
This disease is caused by a fungus and appears as dusty
reddish-brown spots on the leaves and stems. Later these spots
take on a darker appearance and become more firm. In Connecticut,
this disease has not been severe since rust-resistant cultivars
were developed. When it does appear, it usually occurs too late
in the season to cause much damage.
If the disease appears during the growing season, it may become
necessary to spray with compounds. Control can also be achieved
with the use of fungicide sprays applied as soon as symptoms are
visible. Among the compounds registered for use in Connecticut is
mancozeb. Consult the label for dosage rates and safety
precautions.
Purple spot, Pleospora herbarum.
The disease is caused by a fungus and appears on the ferns as tan
to brown lesions with dark purple margins. As the lesions
coalesce, the fern needles begin to drop off and cause
defoliation. On the spear, the disease causes small (1-2 mm)
elliptical purplish spots which can lower marketability. Lesions
usually appear on one side due to the wounding effect of
wind-driven sand.
Burial or removal of the previous year's fern growth lowers the
inoculum and reduces the severity of purple spot. Cover crop
mulches and wind barriers that reduce blowing sand can reduce the
disease. Control can also be achieved with the use of fungicide
sprays applied as soon as symptoms are visible. Among the
compounds registered for use in Connecticut is chlorothalonil.
Consult the label for dosage rates and safety precautions.
Diseases caused by Physiological/Environmental Factors:
Frost damage.
Spears appear slightly darker green, water-soaked and break
off easily. Soft-rotting bacteria can enter the damaged tissue.
New spears may take several more days to emerge.
If frost is imminent, all spears should be harvested beforehand.
Do not compensate for the lost yield by extending the harvest
season.
Fasciation disease.
An abiotic disease that causes the stem to flatten and become
grossly distorted. This disorder is a genetic mutation and will
not spread.
Cut and discard the stem at its base to prevent insects from
feeding and reproducing on the stem.
Insect Problems
Asparagus aphid, Brachycorynella asparagi.
This blue-gray aphid overwinters as eggs on fern residue left in
the field. When the eggs hatch, the aphids feed on spears and
then the fern. Aphid feeding causes a bushy "witch's
broom" growth and a blue-green color to the fern. When
present in large numbers, these aphids can damage or kill the
plants. For more detail on control measures,
see Aphid
fact sheet.
Asparagus miner, Ophiomyia simplex.
This miner tunnels near the base of the stem and just beneath the
epidermis. The resulting brown streaks in the stalk near the base
of the plant may affect commercial salability, but do not greatly
affect plant health. High miner populations were once believed to
cause yellowing of the foliage, but this is now known to usually
be caused by Fusarium diseases. Some of the mines start a
foot or more above the soil and the miners work downward, often
beneath the soil surface. The adult resembles a house fly, but is
only 1/10" long. Adults emerge during the first week in
June, and there are two generations each season. The insect
passes the winter in the burrow, in the form of a pupa resembling
a flax seed. Pulling and destroying old stalks in late fall will
destroy overwintering puparia. Four parasites, Dacnusa rondani,
D. bathyzona, Sphegigaster spp. and Pleurotropis
epigonus, help to restrain miner populations. Chemical
control is not usually necessary.
Common asparagus
beetle, Crioceris asparagi.
This is a bluish-black beetle with three cream-colored spots and
an orange outer margin and tip on each wing cover. The thorax is
reddish and usually bears two black spots. This beetle is about
1/4" long and hibernates under rubbish, bark of trees, or
similar situations where it can find shelter. Emerging from
winter quarters at the time the shoots appear, the beetles eat
the tender shoots, often causing considerable injury. The females
lay eggs on the shoots early in the season and on the leaves and
flower stems later. The larvae that hatch from the eggs are gray
with black legs and head. They can damage the shoots near the end
of the cutting season and also feed on the leaves and the
epidermis of the stalks. New plantings and new ferns produced
just after harvest should be protected as defoliation weakens the
plants. Cutting the shoots very cleanly just below ground level
every 1-2 days during the harvest season will remove many of the
eggs before the larvae can hatch. A tiny parasitic wasp, Tetrastichus
asparagi (1/16 inch long and metallic green), also destroys
many of the beetle eggs and larvae. Among the compounds
registered for use to control this pest in Connecticut are
rotenone, pyrethrum, carbaryl or malathion. Consult the label for
dosage rates, safety precautions, and during the cutting season,
be sure to observe the required interval between an insecticide
application and resuming the harvest.
Spotted asparagus beetle, Crioceris duodecimpunctata.
The spotted asparagus beetle is slightly larger than the common
asparagus beetle. It is reddish brown or orange in color, and has
six black spots on each wingcover. The adult beetles feed on the
tender shoots with the common asparagus beetles. The larvae of
this species feed inside the asparagus berry and do not damage
the shoots or ferns. Many new varieties of asparagus are all male
and have no berries, and thus have very few spotted asparagus
beetles. Control of this species is usually not necessary.