Alan
McNab
Professor of Plant Pathology |
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Wilts are caused by
several agents. Four common wilts that can be confused with eachother
are Verticillium wilt, Fusarium wilt, bacterial wilt, and walnut
wilt. Information on varietal resistance, range of crops affected,
proximity to walnut trees, soil temperature, and past cropping history
help determine which of the wilts is present. usually a laboratory
isolation is needed to verify the causal agent. Bacterial canker,
southern blight, leaf roll, root knot, and stem rot -- five other
disorders often mistaken for wilts -- are also described here.
Verticillium
Wilt
Fusarium Wilt
Walnut Wilt
Bacterial Wilt
Bacterial Canker
Southern Blight
Leaf Roll
Root Knot
Stem Rot
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Leaf Spots and Blights, caused
by several different agents, include early blight, late blight, Septoria
leaf spot, gray leaf spot and bacterial spot.
Early
Blight
Late Blight
Septoria Leaf Spot
Gray Leaf Spot
Bacterial Spot
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Fruit Spots and Rots frequently
observed are anthracnose, soil rot, early blight, late blight, buckeye
rot, blossom-end rot, bacterial spot, bacterial speck, bacterial
canker, and ghost spot.
Anthracnose
Early Blight
Late Blight
Buckeye Rot
Soil Rot
Bacterial Spot
Bacterial Speck
Bacterial Canker
Ghost Spot
Blossom-End Rot
Catface
Sunscald
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Internal Browning and Graywall (Blotchy Ripening) are
thought by some scientists to be two different disorders with similar
symptoms. Affected green fruit has grayish brown blotches on the
shoulders; internal wall tissue is brownish. As fruit ripens, discolored
blotches are yellowish on an otherwise ripe fruit.
Internal browning is the name given to a fruit disorder caused by
tobacco mosaic virus. SYmptoms will develop on fruit approaching maturity if
plants are infected at this late stage of fruit development. Fruit on one or
two clusters may be severely affected while other may be symptomless. Symptoms
are less likely to appear on fruit if plants are infected during an early stage
of fruit development. Graywall (blotchy ripening) is the name given
to a fruit disorder that has been associated with specific environmental factors
and possibly bacteria. The cause is not clearly understood. Graywall is promoted
by low light intensity (a condition prevalent among dense vines), low temperature
levels, excessive soil moisture, excessive soil compaction, high nitrogen levels,
and low potassium levels. |
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Viruses and Herbicides often cause
leaf deformation that is most severe on new growth. Tobacco mosaic,
cucumber mosaic, and 2,4-D are three common causes of these symptoms.
Tobacco Mosaic
Cucumber Mosaic
Double-Virus Streak
Spotted Wilt
2,4-D Herbicide Injury
Lightening Injury
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