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Leaf spots can vary in size, shape, and color depending on the age and type of the cause or pathogen. Plants, shrubs and trees are weakened by the spots on the leaves as they reduce available foliar space for photosynthesis. Other forms of leaf spot diseases include leaf rust, downy mildew and blights. [4]
When lettuce is infected with INSV, it shows a number of symptoms, such as yellowing leaves, dead spots, and stunted growth. On the inner leaves there are patterns of necrosis and chlorosis. At the base of the ribs of infected lettuce plants there is significant necrosis and lesions. The necrotic tissue can look brown to dark brown.
Hoya carnosa Hoya mindorensis, Sydney, Australia.. Hoya is a genus of over 500 species of plants in the dogbane family, Apocynaceae, commonly known as waxflowers. [2] Plants in the genus Hoya are mostly epiphytic or lithophytic vines, rarely subshrubs, with leathery, fleshy or succulent leaves, shortly tube-shaped or bell-shaped flowers with five horizontally spreading lobes, the flowers in ...
Hoya meliflua has stiff succulent leaves with a very clean look to them with no venation. The flowers are reddish orange and have nectaries near the base of the central column from which a dark sap is produced that stains very easily.
As the season continues into summer, apothecia begin to form, giving rise to brown-black leaf lesions that resemble spots of tar. [2] Leaves retain their yellow border from the initial chlorosis. Apothecia survive in the fallen plant debris over winter, releasing spores when the temperature is warm again. [5]
Stegophora ulmea is a foliar disease of elms commonly known as black spot of elm, twig blight, and elm leaf scab. [1] It is characterized by yellow spots that become black spots on the leaves. The pathogen is an ascomycete fungus native to North America. Stegophora ulmea is its teleomorph name. [2]
Infected leaves are filled with numerous black lesions that cover an obvious portion of the leaf. [5] These lesions first appear as small purple spots which turn red to brown and then black. Most spots are circular but can amalgamate to form large, irregular dead patches. [6] These spots tend to enlarge and separate from healthy tissue.
Black spot leaf disease is a physiological plant disorder that affects some grape varieties such as Concord.It is essentially a potassium deficiency that causes the leaves on a vine to turn purple and eventually black as chlorophyll is lost.