Crop Production News - 2018
By Mackenzie Hladun, Dutch Elm Disease Technician, Regina
Dutch elm disease (DED) is an infectious disease in elm trees caused by the pathogen Ophiostoma novo-ulmi. This fungus is spread by the elm bark beetle, which will feed on an infected tree, resulting in spores of the DED pathogen adhering to the beetle. The beetle also breeds under the bark of the elm tree, resulting in a new generation of infected beetles feeding on other healthy elms. This causes the disease to spread. A similar disease is Dothiorella wilt, caused by the pathogenic fungus Dothiorella ulmi.
In Saskatchewan, DED was first detected in 1981, but disease surveillance and the removal of infected trees have helped keep the disease in check. The distribution of DED in Saskatchewan is illustrated in the 2017 Known Extent of Dutch Elm Disease in Saskatchewan map. Both DED and Dothiorella wilt are detrimental to elm trees because they affect the tree’s ability to move water. Water must be moved from the roots of the tree to the leaves, and everywhere in between, in order for the tree to generate energy and survive. Infection by the DED and Dothiorella wilt fungi prevents sufficient movement of water throughout the tree, resulting in the following symptoms:
- Brown staining of the internal wood; and
- Yellowing/browning, wilting and/or curling of leaves.
The ultimate result of DED or Dothiorella wilt infection is death of the tree. Preventing the spread of DED can be accomplished by getting suspected trees diagnosed. Both DED and Dothiorella wilt can be identified via culturing infected wood.
The provincial Crop Protection Lab tests for DED and Dothiorella wilt. Testing is free for Saskatchewan residents and is concluded within 15 business days. To submit a sample, follow these simple instructions:
- Examine the elm tree. Look for yellow/brown wilting or curling leaves.
- Only sample an elm tree between June 1 and Sept. 30. Infected leaves may be confused with leaves changing colour in the fall.
- Sterilize your pruning tools with 10 per cent bleach, 70 per cent rubbing alcohol or gas line antifreeze.
- Choose a branch showing symptoms of wilting or flagging. Infected wood may appear to be stained brown. To confirm, peel back the bark and look for brown staining in the sapwood, or just under the bark. While staining is a strong indicator of DED, it is not always present in a diseased tree.
- Select a smooth and straight branch, without any cankers or knots, that is not dried out or dead.
- Ensure each branch is one to 1.5 cm in diameter (about the size of your index finger).
- Each piece should be 10 to 15 cm long.
- Cut three to four branches.
- Please do not send elm leaves, elm trunks or large branches to the lab.
- Remove the leaves and twigs from the cut pieces of the branch, but do not remove the bark.
- Wrap all branch pieces in wax paper and secure with tape to prevent drying.
- If sampling more than one tree, be sure to sterilize your pruning tools between each tree. Keep each sample separate and clearly marked/identified.
- Place the sample(s) in an envelope. Make sure to include your name, address, phone number and the location of the tree(s).
- Send the sample as soon as possible to:
Crop Protection Laboratory
346 McDonald Street
Regina SK S4N 6P6
Important Points to Remember
- Samples can be submitted between June 1 and Sept. 30 each year. Samples will not be accepted after Sept. 30.
- If the sample needs to be stored temporarily prior to submission, it should be kept in a cooler or a fridge to prevent deterioration.
- Ensure that the sample is taken from a branch showing symptoms; otherwise, the results may not be accurate. A positive result means DED is present on the sample and the tree must be removed. A negative result indicates the absence of the disease.
What to do When the Tree Tests Positive for DED
- DED is provincially regulated under The Forest Resources Management Act and is federally regulated under The Plant Protection Act. Trees confirmed to have DED are to be removed immediately, and the wood must be promptly disposed of at the nearest elm tree disposal site. The Saskatchewan Ministry of Environment will be notified of any positive results.
- To find out more about DED and what you can do about it, or if you suspect an elm tree has the disease, contact the Saskatchewan Ministry of Environment DED line at 1-800-567-4224. Contact your local municipal office for more information about infected elm tree or wood disposal sites.