Bulbs
Plant Health Problems
There are a number of diseases which are common to all plants considered
"bulbs" although their impact and relative importance can vary from
genus to genus.
Diseases caused by Fungi:
Leaf scorch, Stagonospora curtsii.
This fungus infects leaves, flower stalks, flower parts, or bulb scales.
Affected plant parts are often bent or deformed at the point of infection.
Brown spots or blotches with yellow borders develop on diseased tissues. Flower
stalks of plants with severe infections often dry up without producing flowers.
Since the fungus is probably present in the bulb, infections occur as flower
stalks and leaves emerge from the bulb.
Control can be achieved by minimizing moisture on the leaves and flower stalks
by careful watering. It is also helpful to provide good ventilation and plenty
of light since these will decrease the chance of spreading the fungus. Heavily
infected bulbs should probably be discarded.
Bulb rot, Penicillium, Fusarium.
This disease often develops during storage and is frequently associated with
mechanical injury or damage from mites. Infection is favored by moist
conditions. Infected bulbs have a dry, punky rot and the bulb scales are often
covered with the characteristic blue-green (Penicillium) or pink (Fusarium)
colored growth of the fungus.
Control is achieved through careful digging to avoid wounding. It is also
helpful to control insect and mite pests. Infected bulbs should be destroyed.
Botrytis blight, Botrytis spp.
This is one of the most widespread and common disease of bulbs. Symptoms are
variable and can appear as oval or circular spots which are initially
reddish-brown and develop pale centers and purplish margins. These spots may
run together and rot the entire leaf. These can progress into the stem and
cause the stalk to fall over. If the spots dry out, they turn brown or gray.
Buds or flowers may turn brown and rot and are often covered with the
diagnostic gray, fuzzy growth of the fungus. This disease shows up and spreads
rapidly under cool, humid conditions, especially if plants are crowded.
Control involves raking and removing any affected plant parts after the tops
are killed in the fall. It is also helpful to avoid overhead irrigation and
crowding of the plants. When conditions are favorable, applications of
fungicides can be made when new growth emerges in the spring. Among the
compounds registered for use in Connecticut are chlorothalonil,
thiophanate-methyl, iprodione, and mancozeb. Consult the label for dosage rates
and safety precautions.
Diseases caused by Bacteria:
Soft rot, Erwinia carotovora.
Infected plants fail to flower or blossoms fall off before they open. Tops may
appear water-soaked and collapse. Infected bulbs have a strong odor and are
soft and mushy.
Since this pathogen is highly contagious, all infected bulbs should be
discarded. Bulbs should be planted in well-drained soil and watered early in
the day. This disease can also be minimized by avoiding overcrowding and
wounding during cultivation. Sanitation is also very important. All equipment
should be disinfested between use with 10% household bleach, 70% alcohol, or one
of the commercially available compounds. It is also helpful to control insects
and mites since injuries associated with their activity provide sites for
infection.
Insect Problems:
Aphids, Anuraphis tulipae.
The tulip aphid, Anuraphis tulipae, is perhaps the most common and most
troublesome aphid on tulip, and is more apt to cause injury on forcing bulbs
than those grown outdoors. It also winters on stored gladiolus corms. Immersing
the infested bulbs or roots in 110º F water for 30 minutes will destroy the
insects. Among the compounds registered for control of this pest in Connecticut
are methoxychlor and malathion. Infested bulbs may be dusted with methoxychlor
or dipped in a malathion solution for effective control. Consult the label for
dosage rates and safety precautions. Exposure to the treatment should last for
several hours before the bulbs are planted or returned to storage.
Imidacloprid, applied as a drench, will provide season-long control.
Bulb fly, Merodon equestris.
The maggot of this fly infests the bulbs and ruins them. There is only one
maggot in a bulb, and the insect has one generation each year. The larva
overwinters in the bulb, and pupation occurs in the spring in the old burrow or
nearby in the soil. The adults appear in early summer and lay oval white eggs
near the base of the leaves or on exposed portions of the bulbs. The maggot is a
yellow or dirty white larva without legs. It is about 3/4" long. The fly is
about 1/2" long, black, and banded with yellow or gray, is hairy and resembles a
bumblebee.
Destroy all infested bulbs after digging. Three hours of hot-water treatment at 110º F will be helpful in control. Small, stunted and otherwise obviously infested plants may be dug up and burned, thus preventing the spread of the infestation.
Bulb mite, Rhizoglyphus echinopus.
This mite injures nearly all kinds of bulbs. Easter lily plants in greenhouses
have been severely injured. The mites breed continuously in greenhouses or
wherever the temperature and moisture are sufficiently high. It is possible for
10 or more generations to mature in a year. When the conditions become
unfavorable to the mite, such as lack of food or moisture, a resistant stage
called hypopus is formed. It is adapted for migration to fresh food supplies.
The control measures are: burn all soft and decayed bulbs, if allowed; store bulbs at about 35º F. Heat treat bulbs before storage (see also bulb fly, above).
Garden
millipede,
Julus hortensis.
These millipedes frequently attack the bulbs in tulip beds, especially in old
beds where the bulbs are not reset each year. They eat into the bulbs and the
mutilation is followed by decay. Sometimes all the bulbs are destroyed. When
abundant, these millipedes also injure other bulbs, strawberry plants, and the
roots of various other plants. Tulip bulbs may be dug after flowering, kept cool
and dry, and planted in the fall. Dusting the soil surface with diazinon, which
is among the compounds registered for control of this pest in Connecticut, will
be helpful in managing this pest. Consult the label for dosage rates and safety
precautions.
Lesser bulb fly, Eumerus tuberculatus.
This fly is also a pest of onion, but it most severely injures narcissus. It is
believed that there are two generations each year. The flies appear in May and
June and lay eggs at the base of the leaves. The larvae find their way to the
tip of the bulb and then go downward into the interior. As many as 77 larvae
have been found in a single bulb. When fully grown, these maggots are between
1/3 and 1/2" long, wrinkled and dirty grayish yellow in color. They pupate
in August in the bulb or in the soil near it. Certain larvae overwinter in the
bulbs, but these are thought to be the second generation, from which flies
emerge the following spring. The fly is about 1/3" long, and has gray
wings and a black abdomen marked with three white crescent-shaped bands.
See bulb fly, above, for control.