I have a row of 11 spruce trees that are planted in a narrow strip of land between two parking lots. They were topped years ago and now are about 70 feet tall. There is a narrow strip of grass alongside that I fertilize and water just enough to keep the grass alive but dormant in the summer, but not lush green. I do understand that conifers need a summer drought because of their evolution. Last year I contacted a national tree service about a a noticable decline in one of the trees. The diagnosis was black aphids. They recommended a root injection of a systemic pesticide because the trees were too big to spray. Unfortunately they were unable to do anything because the only chemical wasn't registered for use on spruce. I was left with no solution. This year I have seen aphids, scale and woodpecker damage (bark beetles?) on three trees. The decline of the first tree is quite significant now. I'm sure that if one tree has these problems then they all do. I want to keep all of these trees but understand that having 11 large trees in 1500 square feet of exposed land wasn't the best plan then or now. I fear one of the best solutions is to remove a few of them to allow the remainder to survive with less competition. Culturally I can't change their surroundings and I'm unsure as to the effects of applying more or less fertilizer and water to large conifers. I appreciate all of your pest control recommendations.
Buggy spruces are a common sight in local metropolitan areas. Even native Sitka spruce is healthier on outer coast and in lower mountains than in drier climates between. Likely you will either have to remove your grove of Norway spruce or continue with pest controls.
I'd be inclined to thin out the poorer trees (particularly that sickly-looking one ?4th from the left) to give the rest more space.
I cant see where a little extra water could hurt? Black aphids can be controlled by just painting cygon on the bark. But I would like to know the name of the root injection systemic insecticide that your tree company said they couldn't use. I've been spraying trees a long time around Vancouver, and never new there was such a product registered in BC for any tree. Also bacterial blight leaves the same damage as black aphids do on Spruce trees, declining of older needles, and the over all health of the tree. As well as this blight will single out a certain tree, aphids don't care and generally effect all the trees in a short stand like that. Could'nt hurt to get a second opinion, or a plant lab test done. If there is a disease, then the tree, trees may be dying, if it is only a pest, then I would water the crap out of them. We have had some pretty dry years in Vancouver, Jim.
Thanks for all of your replies. I will have the weekest tree removed and then water the rest aggressively. Then I'll try the Cygon. I hadn't thought of the blight possibility. My biggest concern is the woodpecker damage and pitch flowing down the trunk. They're after something under the bark. The tree company never told me what the chemical was. In fact I never received a report. After their site visit I had to repeatedly call them to find out what the problem was and what to do. My earlier post explained what they said.
