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Page 37:
https://www.seminis.com/SiteCollecti...ease-Guide.PDF
white tip
Symptoms:
Initial infection mainly occurs at the leaf
tip and less frequently between the leaf
tip and mid-leaf. Disease first appears
as water-soaked spots that expand into
lesions. Lesion margins remain watersoaked
as affected tissue wilts and
dries to the bleached white appearance
for which this disease is named. When
environmental conditions favor disease
development, secondary lesions elongate
to the base of the leaf. Crop losses are
generally due to reduced plant weight
in leek and storage rot of onion bulbs.
Total crop loss may occur under severe
disease pressure.
Conditions for
Disease Development:
Phytophthora porri oospores can survive
for years in soil. High humidity and
rainfall combined with low temperatures
[15°C (59°F)] favor disease development.
This disease tends to be more severe
in fields with poor drainage. Once the
disease is established, wind-borne and
water-splashed sporangia and zoospores
are easily spread.
Control:
Avoid sprinkler irrigation. Rotation to nonhost
crops helps to reduce soil inoculum
levels and losses from this disease. Some
fungicides may be efficacious during early
stages of infection