There are numerous trees in the pacific northwest. Many are conifer trees. The main tree of choice in Vancouver and surrounding areas is the Douglas-fir tree. This is because it grows deliciously in all of the forest regions, and its wood is preferred by millions worldwide. Its wood is durable and strong. The Douglas-fir grows best in open sunlight, making it an exceptional choice for cleared land. The Douglas-fir has 1-inch long needles, yellow-green in color, and is commonly known as the Christmas tree. Something else you may not know about the Douglas-fir is that it is the most important lumber tree in the USA & Canada!
Diseases and Insect Identification and Control – The Douglas-fir is susceptible to the following diseases:
1. Rhabdocline Needlecast – March through May is the time to watch for this one. The needles from the previous year will get yellow spots on them. Left unattended, these spots enlarge and become yellow-brown patches, and eventually the leaves fall.
2. Swiss Needlecast – March through June is the season for Swiss Needlecast. Similar, but not nearly the same as Rhabdocline Needlecast, this type of Needlecast will brown the needles making them fall off. If you get a magnifying glass, you will find rows of black fruiting bodies on the underside of the needle along the spine.
3. Twig Blight – A disease that causes twig tips to curl downwards and die, leaving small black growths dotted along the dead tissue.
How to Combat and Treat Diseases
These trees need good air circulation. Maintain effective weed prevention and control techniques, so that air moves freely through the tree. After about 10 percent of the buds have opened, apply a fungicide. Apply again a week later, and again 3 weeks after all buds break. If cold temperatures last through the spring, causing the new shoots to mature slowly, apply fungicide a fourth time 2 to 3 weeks after the 3rd application.
For Twig Blight
Prune and destroy affected tips for best control.
Insects That Affect Douglas Fir
Douglas-fir Twig Weevil – These insects will cause damage that destroys twigs, and small branches.
Douglas-fir Engraver Beetles – These beetles kill patches of cambium on the stem, and could likely lead to branch or top kill.
Round Headed Wood Borers – By the time these insects start causing damage, the tree is usually dead or dying, but they start to infest the branch collar area and the main trunk of the tree first.
Flat Headed Wood Borers – These insects attack and infect the entire tree. The adults fly from May to September. It is said that stocking control, as well as other vigor-enhancing treatments, may be an effective way for reducing insect damage.
Douglas-fir Beetle – Namely the most destructive beetle attacking Douglas-fir trees in the Pacific Northwest. You can identify damage by a reddish-brown dust left behind in holes near the base of the tree, from the beetles boring. These beetles tend to attack trees that have suffered severe stress, such as drought, fire, etc. They may attack other trees, but successful breed development has only been reported in downed trees. The beetles multiply rapidly in the downed trees, and then begin to move out into greener ones. By keeping trees in good condition and health, and removing tree waste, you should be able to keep the beetles at a minimum. Extremely cold temperatures can kill breeding beetles, and hotter weather with droughts will let them flourish.
Treating Insects – Have a tree professional applicator assess the damage, and treat accordingly. For any fungus related diseases, the common treatment is pruning, and/or fungicides.
1. Douglas-fir does not like extreme drought.
2. The Douglas-fir tree does not like extreme drought.
3. Several canker-causing Fungi can attack and kill branches of severely drought-stressed Douglas-fir. Look for signs of fungi right after a drought subsides.