Dutch Elm Disease Diagnostic Guide
Dutch elm disease (DED) is a fatal disease of elm (Ulmus sp.) caused by the fungus Ophiostoma novo-ulmi. Introduced to the United States in the 1930’s the disease has killed millions of elm trees and remains a key focus for urban foresters throughout the country. The fungus can be spread by root graft transmission but is most commonly vectored from diseased trees to healthy trees by the European elm bark beetle and the native elm bark beetle.
Trees at Risk
All native American elms are at risk from Dutch elm disease. Asian elms and hybrid cultivars of elms can be resistant but are still known to be susceptible.
Signs of Damage
- Dutch elm disease symptoms begin to develop 4-6 weeks after infection.
- Wilting or "flagging" of one or more branches, usually starting at the branch tip.
- Leaves on infected branches turn dull green to yellow, curl, and become dry and brittle.
- As the infection spreads, the sapwood beneath the bark displays a brown discoloration.
- None without magnification.
- The fruiting bodies (pycnidia) of the fungus can be seen under a microscope.
Dutch Elm Disease spreads overland by Elm Bark Beetles and below ground by root grafts. The elm bark beetle feeds in the 2-4 year old branches of healthy elms. If the beetle is carrying the disease spores on its body, it introduces the fungus at that time. Thus, the purpose of Arbotect® macro infusion is to evenly and completely cover all the 2-4 year old branches with enough fungicide to keep the fungus from being able to grow. Arbotect® is diluted and macro-infused with high volumes of water to ensure complete and even distribution of the fungicide in the crown of each tree.
Arbotect® protects elm trees for 3 growing seasons from Dutch elm disease using the Rainbow macro-infusion system.
Arbotect® DOES NOT protect Elms from root graft infections and Arbotect® DOES NOT SAVE DISEASED elms without pruning out the infection.
* Reduce the dosage rate for trees < 20 inches that are missing canopy. Reduce the dosage rate by the % of canopy missing, for example if 20% of the canopy is missing, reduce the dosage rate by 20%. Do not reduce the dose for trees over 50” DBH.
Tree Injection using Arbotect 20-S
Notes: Reduce rate for trees < 20 in if missing canopy. Reduce rate by the % of canopy missing i.e. 20% of the canopy is missing, reduce rate by 20%. Do not reduce for trees over 50 in DBH. Dosage: American Elms: 2.4 fl. oz. Arbotect®/DBH” All Other Elms: 1.2 fl. oz. Arbotect®/DBH” Dilute each 2 fl. oz. of Arbotect 20S in 1.0 gallon of water Timing: After full leaf expansion in the spring (coincides with seed drop) and may continue through the growing season until just prior to the onset of fall color. Re-Treatment: Every 3 years. In areas of high disease pressure, re-treatments at 2 - 2 1/2 years may be warranted.
- Protects healthy elms from beetle transmission of Dutch elm disease.
- Arbotect is the only fungicide known to move into new tissue each spring.
- 99% success rate.
- Arbotect 20S does not prevent root graft infections.
- Arbotect DOES NOT SAVE DISEASED elms without pruning out the infection.
A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy forestryimages.org. Use of the images does not imply endorsement of treatments by forestryimages.org