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I am working with an apartment complex here in town who thinks their pine trees have needle blight. They were told this by their manager from Western MT and have begun cutting down and disposing of the most severely infested trees. When I went and looked at the trees, I found a severe scale infestation. I am attaching pictures to this email of some of the trees and the infected branches. I have some branch samples in my office I can send to you if that would help. I don’t know anything about pine needle blight or what to look for, but if this is treatable, I would really like to help them out. The needles on the trees are similar in pattern to mugo pines, but the trees generally have a single trunk and are pretty large. I don’t know for sure what species they are. In general, the current year growth is the least damaged.
In the more infested tree (pictures 446-the tree
on the right and 448) the dying needles are twisted and orange. In the less infested tree (next email) (Pictures 451, 452), the dying needles tend to be the older growth, but are also interspersed in the newer growth. This could well be a very severe scale infestation, but I would appreciate any information you can provide me about needle blight!
The trees appear to be either scotch pine or really stunted Austrian pines, probably the former. As such they are maladapted to Montana and thus stressed. In addition to the pine needle scale (white waxy flecks on needles) it appears they have been in contact with 2,4 D – probably as a result of weed killer in the lawn. Evidence of this are the twisted needles at the terminal end of the branches - 2,4 D stimulates certain growth auxins causing abnormal and twisted needles growth. Since this is this year’s growth it was probably applied early this summer or spring. They also do have what appears to be needle blight, which is a common name for one of several needle fungi that affect all pines though especially exotic ones. This fungus infects needles and feeds on the carbohydrates within them and then fruits either as spots or dark bands on the needles. It is favored by humid weather and can be enhanced in yards by frequent watering that creates a humid microsite. The banding appears evident on the pictures you sent me. What to do? Dormant oil spray for the scale insects, a broad spectrum fungicide for the needle cast disease such as Daconil or Bordeaux mix , applied shortly after a rain when the fungus is particularly active, and perhaps a generic 10-10-10 fertilizer for the tree applied in late spring of next year. Spraying new needle growth with fungicide shortly after it has elongated in the spring of next year will help keep the fungal problem in check, as will raking up and disposing of dropped infected needles. This of course realizing that the trees are not especially well adapted for Montana – though they can be grown here – they just tend to suffer an inordinate amount from pests and pathogens.
Poor Douglas-fir crowns
Attached are the pictures of the diseased trees we discussed. I am anxious for your feed back on what may be wrong with these trees.
Reply: Dear poor tree crowns:
Dead tree tops and thinning crowns are a typical symptom for drought stress. Drought stress can be brought on by many circumstances that do not necessarily relate to climatic drought. In this case the Douglas-fir trees are most likely suffering from root dieback brought on by excessive landscaping fill being placed over the trees root system thereby starving them of oxygen which tree roots need to respire. This kind of root stress can also cause root diseases of Douglas-fir such as Armillaria spp. or Phaeolus schweinitzii (cowpie conk) to become active on the tree and further cause root damage. With fewer functional roots the tree(s) cannot absorb enough water to keep the crown healthy. The last part of the tree to get water is the top of the crown, so under water stress this is the first part of the tree to die back. Such damage and disease is difficult to control. If you want trees in this location I would suggest planting a tree species that is not as susceptible to Douglas-fir root diseases such as ponderosa pine, western larch, or if the site is moist enough blister rust resistant western white pine. Removing the afflicted trees is an option to consider as they may recover or they may die. Mature trees suffering this kind of damage rarely recover fully and there is conflicting evidence that about whether leaving trees infected with root disease will enhance the pathogenicity of the root disease to afflict neighbor trees. An argument is that the stumps will feed the root disease, another argument is that a live tree will continue to "feed" the root disease even more. There is also conflicting evidence of the effectiveness of pulling out the stumps. In forests root diseases often take out groups of trees, perhaps because they are related and exhibit the same genetic weakness or because the root disease gains strength from one tree and can attack others - we don't know. In all such cases, introducing a less susceptible species is a good idea.
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