Outbreaks of sawfly larvae can defoliate trees and may cause dieback, stunting or death. The caterpillars can completely defoliate trees if large quantities are present. The caterpillars can completely defoliate young citrus trees (below 2 feet) and devastate citrus nurseries. An infestation of the larvae can defoliate an oak tree. Mopane worm outbreaks defoliate shrubs, depriving game of browse. Biological warfare can also specifically target plants to destroy crops or defoliate vegetation. The larvae are most detrimental to younger trees, which they can more thoroughly defoliate. Leaf-eating insects, especially the forest tent caterpillar, Malacosoma disstria, occasionally defoliate trees. These lichens can be red or orange colored and are known to defoliate rocks. After extensive research, "Aphalara itadori" has been shown to defoliate knotweed species substantially. The pathogen-caused leaf spot disease can almost defoliate "V. agnus castus". Cyclones can defoliate an area, knock down canopy trees, and create landslides and flooding. It can defoliate trees and eat smaller plants to the ground. A colony can "[defoliate] a mature eucalyptus tree overnight". In extreme droughts, it may defoliate completely.