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.
Treatment Strategy
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. 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.
Other Treatment Practices
- Promptly remove infected trees.
- Remove bark from any elm firewood.
- Trench between infected and health trees to prevent root graft transmission.
- Diseased trees may be saved by utilizing the Tracing technique to remove the fungus from the tree and then treating the remaining tree with Arbotect 20-S. Alamo (propiconazole) may be used the year this process is preformed, followed by an Arbotect treatment the following year.
Tree Injection Using Arbotect 20S
Expected Results
- 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.
- *Do not treat Camperdown elm (Ulmus glabra 'Camperdownii')
Signs of Damage
- Dutch elm disease symptoms begin to develop 4-6 weeks after infection.
- The first noticeable symptom that results from the fungal occupation of the water conducting vessels is 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 wood beneath the bark displays a brown discoloration. Using leaf symptoms alone to determine where the leading edge of the infection is does not work.
- To determine where the leading edge of the fungal infection is, the arborist must peel back the outer bark and examine the sapwood for staining.
Wilting or "flagging" in the canopy
Vascular Staining
Trees At Risk
- American (white) elm* (U. americana)
- Red (slippery)* elm (U. rubra)
- Rock elm* (U. thomasii)
- Winged Elm* (U. alata)
- Cedar elm (U. crassifolia)
- Siberian elm (U. pumila)
- Chinese elm (U. parvifolia)
*denotes those most susceptible
References
University of MN
https://extension.umn.edu/plant-diseases/dutch-elm-disease
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.
