| Disease |
Symptoms |
Pathogen/Cause |
Management |
| Bulb Basal Rot |
The basal plate is dark brown and
dead. Scales fall off. |
Fusarium
and Cylindrocarpon |
Use pasteurized potting soil. Do
not plant bulbs that have a rotted basal plate. Dip bulbs in
thiophanate methyl before planting. |
| Bulb Storage Rot |
Bulb scales have brown spots and
a severe rot. Bulbs may be soft and covered with a blue-green
mold or white fungal growth. |
Bulbs harvested while still immature
are attacked by Penicillium
(blue mold) or Rhizopus
(soft rot) fungi. |
Do not plant affected bulbs. |
| Botrytis Blight |
Oval to circular reddish-brown spots
form on leaves. Brown spots develop on flowers. |
Botrytis
cinerea |
Maintain humidity below 85%. Avoid
overhead irrigation. Apply mancozeb as a spray. |
| Leaf Scorch |
Semicircular
dead areas develop along leaf margins and may engulf leaf
tips. |
Uncertain. Fluoride toxicity, mineral
deficiency induced by root rots, and low soil pH have been implicated
in scorch. |
Avoid the use of super phosphate
and other fluoride-containing fertilizers. Control root rots.
Maintain a soil pH between 6.0 and 7.0. |
| Pythium Root Rot |
Lower
leaves yellow and die. Roots are limp and dark brown. Flowers
abort. |
Pythium |
Use pasteurized potting soil. Drench
potted bulbs with metalaxyl at planting and switch to other
Pythium-controlling fungicides for later treatments. Or, apply
etridiazole, mefenoxam, propamocarb, or thiophanate methyl +
etridiazole as a soil drench. |
| Rhizoctonia Stem Rot |
Bulbs are yellow rather than the
normal white. Stems and scales where the stem emerges develop
a soft rot, causing
the plant to topple. |
Rhizoctonia |
Use pasteurized potting soil. Drench
potted bulbs with PCNB, flutolanil, thiophanate methyl + etridiazole
at planting. Repeat treatment as stated on the fungicide label. |
| Scale Tip Rot |
The tips of scales turn tan or dark
brown to black in color. |
A complex interaction of Pseudomonas
bacteria and the fungi Fusarium
and Cylindrocarpon appear
to be the cause. |
Do not plant affected bulbs. |
| Twist |
Leaves along the middle stem area
twist while leaves above and below appear normal. |
Uncertain. Combined infection by
various viruses may cause twisting. The bacterium Pseudomonas
may be involved. |
None. Sometimes plants grow out of
these symptoms. In some cases, plants are stunted and never
recover. |
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