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Pyrenophora tritici-repentis and Drechslera tritici-repentis is a necrotrophic plant pathogen of fungal origin, phylum Ascomycota. [1] The pathogen causes a disease originally named yellow spot but now commonly called tan spot, yellow leaf spot, yellow leaf blotch or helminthosporiosis.
Symptoms can overlap across causal agents, however differing signs and symptoms of certain pathogens can lead to the diagnosis of the type of leaf spot disease. Prolonged wet and humid conditions promote leaf spot disease and most pathogens are spread by wind, splashing rain or irrigation that carry the disease to other leaves. [2]
The species are mostly herbaceous perennial plants 0.3–1.5 metres (1–5 feet) tall, but some are annual plants and a few are shrubs up to 3 m (10 ft) tall. An exception is the chamis de monte (Lupinus jaimehintonianus) of Oaxaca in Mexico, which is a tree up to 8 m (26 ft) tall.
Prevention is the best option for management of gray leaf spot as hyphae on plant debris is the primary source of inoculum. [1] There are various cultivars of St. Augustine grass, perennial ryegrass and tall fescue on the market that have variable resistance to gray leaf spot but none are confirmed as completely resistant.
The lesions found in Northern corn leaf blight are more acute if the leaves above the ear are infected during or soon after flowering of the plant. [4] In susceptible corn hybrids, lesions are also found on the husk of ears or leaf sheaths. In partially resistant hybrids, these lesions tend to be smaller due to reduced spore formation.
An albino corn plant with no chlorophyll (left) beside a normal plant (right) In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll.As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white.
A raspberry leaf spot infection initially causes dark green circular spots on the upper side of young leaves, which will eventually turn tan or gray. [3] These spots are typically 1–2 millimetres (0.039–0.079 in) in diameter, but can get as big as 4–6 millimetres (0.16–0.24 in). [4]
There are many ways to try and manage Drechslera leaf spot. The most favorable would be to find a resistant plant variety. Other ways include collecting fallen leaves in order to reduce inoculum from plant debris, as well as pruning to increase air circulation for the grasses (a reduction in moisture is unfavorable to the pathogen). [5]