The variegated red-twig dogwood (Cornus alba "Elegantissima") is a deciduous shrub that grows to a height of between 6 and 8 feet tall, with a 4- to 6-foot spread. In autumn, when the leaves fall, the plant is afire with upright flaming red stems, adding plenty of interest to the winter garden. Variegated red twig dogwood is susceptible to several disease organisms and pests which adds to its maintenance regime. Grow variegated red-twig dogwood in zones 2 through 8 on the U.S. Department of Agriculture Plant Hardiness Zone Map.
The dogwood borer is the larva (Synanthedon scitula) of a small moth that infests the dogwood's bark. It gains access through wounds or cracks, gorging on the cambium. In the process, twigs and branches die -- sometimes the entire dogwood succumbs. Symptoms of an infestation include red foliage that falls from the plant. Bark around the entry points peels away and sometimes a sawdust-like substance is seen on the ground beneath the entry point. Prevent dogwood borer infestations by using caution when mowing around the plant to avoid injuring it. Spray the tree with an insecticide containing permethrin in May and repeat the application every three weeks.
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There is no doubt how deadly dogwood anthracnose is once you know the scientific name of the fungus that causes the disease: Discula destructiva. Symptoms of the disease include leaf spots, either small and purple or larger and light brown. If the disease spreads to the branches and twigs, it causes cankers. Multiple cankers may girdle the trunk, killing the tree. Prune off infected parts of the tree and destroy or dispose of them. Spray the tree with a fungicide labeled for use on dogwood anthracnose. You may have to spray repeatedly throughout the growing season.
Some dogwood problems have nothing to do with disease or insects, and everything to do with how you care for the plant. Many problems can be prevented with sound cultural practices such as watering and fertilizing according to the dogwood's needs. Variegated red-twig dogwood does best when grown in full sun or partial shade. If the tree is failing to thrive in its current location, you may need to move it. The plant is also intolerant of excess moisture in the root zone. Water consistently, but avoid fertilizing in the fall, to allow the tree to harden off before winter.
To avoid lifelong problems, use care when transplanting the new red-twig dogwood in the fall. It requires more protection when planted in this season than others. Amend the soil to ensure proper drainage and pile 4 inches of mulch around it after planting. Wrap the tree to avoid salt spray and high, drying winds.