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Black spot (Diplocarpon rosae) Black spot (class Leotiomycetes: family Helotiales) Diplocarpon rosae syn. Marssonina rosae – Marssonina rosae causes black spots on leaves. [4] The spots, which may be as much as 12 mm across, are generally circular and have an irregular edge often with a yellow halo. Leaves frequently turn yellow and fall early.
Black spot of rose is the single most impactful disease of roses globally. Every year around 8 billion flowering stems, 80 million potted plants and 220 million garden rose plants are sold commercially. [7] All species of roses (Hulthemia, Hesperrhodos, Platyrhodon and Rosa) are affected by black spot
Spots are usually worse on older leaves. Stem lesions are dark brown to black and may cut the stem all the way around its surface. Lesions on stems enlarge and may blacken large areas near the base of the plant. Affected stems are brittle and easily broken. When at its worst, entire stems can be blackened and killed.
Infection causes a black or grey sunken lesion with a characteristic yellow border. [1] [2] On the leaves of some plants, infection can cause dark, water-soaked spots. [3] The lesions can be observed anywhere on the plant. [1] In seedlings, fungal lesions on the stem are a cause of damping-off. [4] Infected seeds appear black or grey. [1]
Other fungicides such as zineb, chlorothalonil and Captan, also treat leaf spot disease and Benomyl specifically treats Cercospora leaf spots, cherry leaf spot and black spot of roses. [7] Thiabendazole is used to treat leaf spot diseases of turf and ornamentals. [7] Both fenarimol and nuarimol are pyrimidines that also treats leaf spot disease.
raphani is a gram-negative, obligate aerobic bacterium that like many other Xanthomonas spp. bacteria has been found associated with plants. This organism is closely related with Xanthomonas campestris pv. campestris, but causes a non-vascular leaf spot disease that is clearly distinct from black rot of brassicas.
Alternaria black spot of canola or grey leaf spot is an ascomycete fungal disease caused by a group of pathogens including: Alternaria brassicae, A. alternata and A. raphani. This pathogen is characterized by dark, sunken lesions of various size on all parts of the plant, including the leaves, stem, and pods. Its primary economic host is canola.
The bacteria can affect the cotton plant during all growth stages, infecting stems, leaves, bracts and bolls. It causes seedling blight, leaf spot, blackarm (on stem and petioles), black vein and boll rot. On cotyledons small, green, water-soaked rounded (or irregular) spots form which turn brown.