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All About American Elms


To ensure that your Denver elm tree has a healthy and long life, it’s crucial to correctly prune and take properly care of it. Before you decide to prune your elm, make sure it’s the right time of the year because pruning at incorrect times can cause injury to an elm and make it more susceptible to diseases. 

Just like many other deciduous trees, the best time to prune them is in early spring. During this season, a thick tissue, called callus tissue, develops quickly over the areas that are pruned. This helps protect the tree from pests and prevents the spread of Dutch elm disease. If you wait until summer to prune your elm tree, it can disrupt foliage creation and slow new growth. 

Elm trees should be pruned once every three years. If you prune your tree more than this, it can inhibit development and can stunt its growth. However, if a leader branch on your elm tree breaks off, damaged, or diseased, immediate pruning is required. To repair a lost leader, you must make sure to prune competing branches. 

A harmful pest to the American elm tree is called the European elm scale, a soft scale insect that attacks a variety of elm trees. If the infestation is large, the tree may be weakened and may cause branch dieback. European elm scale can be treated with products that are applied to the soil at the base of the tree to be taken up through the root system. Some contact insecticides can be sprayed on the scales, but this is rarely used for larger trees. The European elm scale has one generation per year and females begin laying eggs in late May. The insects start hatching in late June through July. Crawlers migrate towards the leaves where they feed until late fall. You can actually see the black insects with white fuzz along their edges of the insect attached to the twigs and branches.  After feeding, they go back to branches for the winter and hide in the bark crevices. Elms with a European elm scale infestation show yellowing leaves leading to premature leaf drop and dieback. Honeydew secretions on the top braches and mold growth are also signs of an infestation. 

Deep root fertilization is a great way to prevent diseases and insect infestations. The process uses a nutrient solution that is injected into the root zone of the trees and helps provide oxygen to the root system. Soil injections start just below the surface and go 12-14 inches deep. Ideally, it should be done once or twice a year. Careful watering and feeding is also crucial in keeping your elm healthy. Your Denver tree service can help find out what fertilizer formula that is best and how often your elm will require it based on its unique needs. Contact us today to make sure that your American elm lives a happy and healthy life. 
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