Seeds can spread plant diseases from one farm to another,
from one State to another, and from a distant country to the other. Some
disease pests may survive for years, safely lodged on or in a seed or on bits
of stem or leaf mixed with the seeds. Many seed borne diseases cannot be
recognized when seeds are examined, and cannot be detected during incubation.
Only by inspecting the growing crop can one be sure that the seeds are free of
viruses, bacteria, and fungi, organisms that cause disease and are called
pathogens. Most seed borne parasites do not affect germination immediately. They
do not harm the seeds but multiply on emerging seedlings, which may then
succumb to the disease. Some seed lots that show high germination in tests are
nearly destroyed when they are planted under conditions that favor development
of the organisms they carry. Below is a short brief of diseases that are
present in lettuce leaf, and their control measures. Lettuce leaf is probably
the most common and popular salad leaf among all other salad leaf, Therefore
one must be aware of the diseases it gets affected with.
Downy Mildew
Lettuce Leaf symptoms of downy mildew first show as angular,
pale yellow patches which are delineated by leaf veins. The underside of the
leaf opposite the yellow patch will show white masses of spores from 7 to 14
days after infection. Downy mildew damaged leaf tissue can be an entry site for
secondary rot producing organisms. These rot organisms may compound crop losses
in the field, and can also cause losses later when the lettuce is in transit.
Control: There are downy mildew resistant varieties of
iceberg lettuce, but no cultivar is sufficiently resistant to all the races of
downy mildew to allow culture without fungicides. Both systemic and contact
fungicides are necessary in a spray program to combat downy mildew. Control of
the disease depends upon good coverage with the fungicide material, timely
first applications, and repeated applications as weather and disease
development dictate. Currently maneb, fosetyl-A1, and at times, copper
compounds are the primary fungicides used for disease suppression.
For more informaton visit: http://www.seedbuzz.com/knowledge-center/article/lettuce-seeds-diseases
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