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A leaf spot is a limited, discoloured, diseased area of a leaf that is caused by fungal, bacterial or viral plant diseases, or by injuries from nematodes, insects, environmental factors, toxicity or herbicides. These discoloured spots or lesions often have a centre of necrosis (cell death). [1] Symptoms can overlap across causal agents, however ...
Unknown (viruslike) Peanut clump. Peanut clump virus. Peanut green mosaic. Peanut green mosaic virus. Peanut mottle. Peanut mottle virus. Peanut ringspot or bud necrosis. Tomato spotted wilt virus.
Gypsy moth populations usually remain low, but occasional increases to very high levels can result in partial or total defoliation of host trees. [ 6 ] According to a 2011 report, the gypsy moth is now one of the most destructive insects in the Eastern United States; it and other foliage-eating pests cause an estimated $868 million in annual ...
Centaurea stoebe. L. Centaurea stoebe, the spotted knapweed or panicled knapweed, [ 1 ] is a species of Centaurea native to eastern Europe, although it has spread to North America, where it is considered an invasive species. It forms a tumbleweed, helping to increase the species' reach, and the seeds are also enabled by a feathery pappus.
Diabrotica undecimpunctata, the spotted cucumber beetle or southern corn rootworm, is a species of cucumber beetle that is native to North America. The species can be a major agricultural pest insect in North America. Spotted cucumber beetles cause damage to crops in the larval and adult stages of their life cycle.
Contrail created by a KLM Boeing 777 over London, England at sunset in 2012. Contrails, short for "condensation trails," are linear cloud formations produced by aircraft exhaust or air pressure changes, usually at commercial cruising altitudes several miles above the ground. [15]
A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, [ 1 ] although the word cyclone is used in meteorology to name a weather system with a low-pressure area in the ...
The terminus of an avalanche in Alaska 's Kenai Fjords. An avalanche is a rapid flow of snow down a slope, such as a hill or mountain. [ 1 ] Avalanches can be triggered spontaneously, by factors such as increased precipitation or snowpack weakening, or by external means such as humans, other animals, and earthquakes.