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PAL Questions: 1 - Garden Tools:
On the Master Gardener phone clinic today, a caller was concerned about wilted and dried leaves on his tree. This seemed to be throughout the tree, as opposed to being only at the top which might have indicated damage from the bark beetle causing Dutch elm disease.
He asked about ELMguard, which is apparently an injectable substance that increases the immune system of Camperdown elms. Do you know anything about this?
I know that there are fungicide injections that are supposed to stave off the demise of elms which are already suffering from Dutch elm disease, but if this is not what the caller's tree suffers from, it would do little good, and might actually cause harm. He should bring samples to the Master Gardener Clinic for diagnosis as a first step.
From the description of the problem, it might be phloem necrosis (also known as elm yellows), which shows up as wilted yellow or brown leaves which drop early, and affects the whole crown of the tree. It is spread by leafhoppers.
Bacterial leaf scorch usually starts with the oldest leaves and progresses through the entire crown. Leaves are brown at the edges and have a yellow halo.
Dutch elm disease does affect Ulmus glabra 'Camperdownii.' This USDA Forest Service page describes it in detail, and compares it with the two problems I mentioned above. It also talks about the use of fungicide injections.
"Foliage symptoms: Symptoms of DED begin as wilting of leaves and proceed to yellowing and browning. The pattern of symptom progression within the crown varies depending on where the fungus is introduced to the tree. If the fungus enters the tree through roots grafted to infected trees (see disease cycle section), the symptoms may begin in the lower crown on the side nearest the graft and the entire crown may be affected very rapidly. If infection begins in the upper crown, symptoms often first appear at the end of an individual branch (called "flagging") and progress downward in the crown."
"Multiple branches may be individually infected, resulting in symptom development at several locations in the crown. Symptoms begin in late spring or any time later during the growing season. However, if the tree was infected the previous year (and not detected), symptoms may first be observed in early spring. Symptoms may progress throughout the whole tree in a single season, or may take two or more years."
"Injecting elms with fungicide. Certain fungicides, when properly injected, are effective in protecting elm trees from infection via beetle transmission. This treatment is expensive and must be repeated every one to three seasons, thus it is appropriate only for high value or historically important trees. The treatment itself also may pose risks to the health of the tree."
"Eradicating Dutch elm disease from newly infected trees. If a new crown infection of DED is detected early enough, there is opportunity to save a tree through pruning, fungicide injection, or both. Eradicative treatment is not possible on trees that have become infected via root graft transmission. Pruning, which can literally eradicate the fungus from the tree by removing it, has a high probability of "saving" a newly infected tree that has less than 5% of its crown affected."
To answer your question about ELMguard, there are serious doubts about its efficacy as an elm immune booster. I did find an article, dated July 2000, from South Dakota State University Extension which states:
"Dutch elm disease is showing a very large increase in the last week or two. Several cities are now reporting a four- to eight-fold increase in the incidence of the disease. Generally when we have a wet May the problem increases for the year. According to Dutch elm disease researchers the wetter years result in the creation of a vascular system that is more susceptible to the development of the disease. We have had several calls from people wanting to use ELMguard to save their trees, particularly those already marked by the city as having the disease. ELMguard is not a fungicide but a product that is designed to increase the tree's ability to fight infection (according to the ELMguard company). It may be an excellent product and we hope to have more information on it later in the year. However the company does not recommend treatments with ELMguard at this time of year or into fall, thus homeowners should not be expect this to save their infected trees. If the city has marked a tree for Dutch elm disease the tree should be removed as soon as possible to reduce the chance of infecting nearby elm."
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March 22 2017 13:26:25