a large, irregular spot or blot.
Plant Pathology.
a diseased, discolored spot or area on a plant.
a disease so characterized, usually accompanied by cankers and lesions.
a skin eruption; blemish.
verb (used with object)
to mark with blotches; blot, spot, or blur: The floor of the forest was blotched with cool, dark moss.
Textiles. of or pertaining to blotch printing, or to the colored ground produced by this process.

1595–1605; perhaps blend of blot1 + botch2

1. splotch, mark, blemish, stain. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
blotch (blɒtʃ)
1.  an irregular spot or discoloration, esp a dark and relatively large one such as an ink stain
2.  to become or cause to become marked by such discoloration
3.  (intr) (of a pen or ink) to write or flow unevenly in blotches
[C17: probably from botch, influenced by blot1]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin & History

c.1600, perhaps a blend of blot and botch or patch.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
blotch   (blŏch)  Pronunciation Key 
Any of several plant diseases caused by fungi and resulting in brown or black dead areas on leaves or fruit.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica


plant disease characterized by splotchy black stain or coating on leaves, stems, and fruit, composed of dark fungal threads (Capnodium, Fumago, and Scorias species) that grow in flowing sap or on honeydew excreted by aphids and other sucking insects. The condition is unsightly but usually not harmful. Control includes spraying or dusting for sucking insects, washing off sticky coatings of sap or honeydew on plant surfaces, and avoiding the wounding of plants.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
In late spring, the plant is covered with fragrant white or pinkish white
  flowers with yellow blotch.
Genetic studies of net blotch resistance in a barley cross.
Similar levels of net blotch were found for both seeding dates.
Treatment thresholds for leaf and glume blotch in wheat.
Image for blotch
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