Tuesday 16 April 2013

Lettuce Seeds – Diseases


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.

No comments:

Post a Comment