Biology Reference
In-Depth Information
and pathogenic on Douglas-fir. Root and crown
rot; of leafy spurge.
Fusarium oxysporum Iris Basal Rot on bulbous
varieties of iris. Plants fail to emerge, or turn
yellow, wilt and die. Roots are few or none. The
bulb is infected at the base, which shrinks; the
husk adheres firmly, sometimes with a white or
reddish mass of mycelium. The rot is more seri-
ous in warm climates and on yellow rather than
blue varieties. De Wit is very susceptible;
Wedgewood is quite resistant.
Control Avoid bruising bulbs in digging; sort
and discard diseased bulbs right after digging;
dry bulbs rapidly.
Fusarium oxysporum Tulip Basal Rot . Leaves
growing from diseased bulbs turn red, wilt and
die; roots are few or none. Bases of bulbs have
a rather firm rot with white or pink felty masses of
spores. The diseased area usually turns chalky.
This is primarily a storage disease in bulb sheds
and warehouses.
Fusarium oxysporum f. sp. batatas Sweet
Potato Stem Rot , a widespread field disease,
destroying more than 50 % of plants in some
fields. This fungus also infects Jacquemontia .
The stem rot is conspicuous about 2 weeks after
sprouts are set. Sprouts are yellow or dead, and
the vines brown or black, often split near the
ground. Some plants develop new roots above
the decayed section and so survive. Sweet pota-
toes from infected plants are small, decayed at the
stem end, with vascular tissues brown. The fungi
winter in stored roots and can live indefinitely in
soil. Varieties Big Stem Jersey, Little Stem Jer-
sey, Maryland Golden and Nancy Hall are very
susceptible; Porto Rico is intermediate; Southern
Queen, Triumph, and Yellow Strassburg are quite
resistant.
Fusarium oxysporum f. sp. cepae Bulb Rot ,
Basal Rot of onion, shallot and garlic. In the
field there is progressive yellowing and dying
back from tips, the roots commonly turning pink
and gradually decaying. The rot is often associ-
ated with wounds of maggots and other insects. In
storage the rot is most active at room temperature
or above.
Fusarium oxysporum f. sp. chrysanthemi -
Fusarium Wilt of chrysanthemum.
Fusarium oxysporum f. sp. gladioli ( F.
orthoceras var. gladioli ). Fusarium Brown Rot ,
Yellows of gladiolus, a major disease in some
sections. Most infection takes place in the field,
but subsequent decay appears in storage. Corm
lesions are first small, reddish brown, more often
on lower half of corm. They enlarge in storage to
irregular to circular, sometimes zonate brown
areas, which do not infrequently advance until
the whole corm is a hard, dry, brownish black
mummy. Infection comes from old corms, the
fungus penetrating through the basal plate and
the center of the new corm. The latter may be
entirely decayed in storage, with the fungus
advancing from the center to the outside, causing
brown to black surface lesions.
Symptoms of yellows, a vascular disease,
include bending of young leaf stalks, cupping of
leaf stalks in older plants, crooked flower stems,
often greener than normal and a curving of
growth away from the side of the corm showing
rot. There is gradual yellowing and dying of
foliage, starting with the oldest leaves. Picardy
and Spotlight varieties are particularly suscepti-
ble. Nitrogenous fertilizers and manures, espe-
cially where phosphorus is low, increase corm
rot.
Control Cure immediately after digging at 95 F
to develop wound periderm and cuticle resistant
to the fungus; use resistant varieties where possi-
ble or a 3-to 4-year rotation.
Fusarium oxysporum f. sp. lilii. Basal Rot of
lily, on bulbs, roots, stems of garden and native
lilies; Corm Rot of crocus, also on freesia and
cactus ( Cereus ). A chocolate rot at base of scales
next to the basal plate progresses until the scales
fall away. The disease is more destructive to
Madonna and some other garden lilies; it is sel-
dom a problem with Easter lilies grown in the
Northwest. Keep bulbs cool in storage, and plant
in cool soil. Infection comes from contaminated
soil as well as diseased bulbs.
Fusarium oxysporum f. sp. narcissi ( F.
bulbigenum ). Narcissus Basal Rot , general on
hardy varieties, rare on polyanthus varieties. Rot
begins at the root plate at base of bulbs and
spreads through central portions first, extension
of the rot being more rapid in affected scales than
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