Burning bush or winged euonymus (Euonymus alatus) is grown for its foliage, so when the shrub begins to lose its leaves, it may be a blow to your landscaping plan. Cold injury can leave burning bush plants susceptible to pest invasion and disease. As a clue to tell you if your plants are stressed, watch for an early change in their leaf coloring.
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The two-spotted spider mite infests a wide range of plants, trees and shrubs; but, according to the University of Kentucky Department of Entomology, spider mites are particularly destructive to burning bush plants. Mites stress the plants, leading to an early change of color in burning bush foliage, browning of foliage and leaf drop. The mites are relatives of spiders. They prefer hot, dry conditions and produce several generations a year.
To check for mites, hold a white sheet of paper beneath a branch, shake the bush and look for dark specks. To fight an infestation, spray your shrubs with water to wash away mites. The mites feed, shelter and create their webs beneath leaves, so direct the spray to the underside of foliage. Horticultural oils and miticides, such as malathion, can treat mites.
Euonymus scale and winged euonymus scale damage burning bush plants by feeding, which leads to leaf drop and stress on plants. Infested plants are susceptible to winter injury.
Keep your plants adequately watered. Use pruning to treat limited infestations. Use horticultural oil, insecticidal soap or the insecticides carbaryl or malathion to treat shrubs when crawlers -- the immature form of the pest -- are present. "Compactus" is resistant to euonymus scale.
While not a major pest in every state, even small infestations of the euonymus caterpillar can lead to defoliation. The caterpillars start creating their webs on the tips of branches and move toward the interiors of affected shrubs. They can spread to affect entire shrubs. Damage is caused by larvae hatched the previous summer. These larvae begin to feed on foliage the following year in May or June.
Prune or remove any webbing and caterpillars. Insecticides, such as carbaryl and permethrin, are useful against these caterpillars. The University of Illinois Extension warns that growers should take care to ensure the insecticide penetrates the webbing for best results.
Environmental stress can cause decline in burning bush shrubs. The symptoms of stress include leaf drop, which can be severe and involve almost complete defoliation of shrubs.
According to the Ohio State University Extension Plant Clinic, samples of affected plants have not shown an infectious agent as the cause, which leads the specialists involved to blame root problems due to moisture and temperature stress. While cold injury occurs due to low temperatures and drought stress, too much moisture leads to the death of root tissues. According to the University of Illinois Extension, the shallow roots then can’t supply nutrients or water, leading to off-color or wilted foliage.