Every tree species is vulnerable to some kind of problem whether it be a biotic disease, a pest or an “abiotic” environment-related disorder. Last week I encountered a fairly unusual one in a tree that is not very common in our region. It is revered in bonsai culture as one of the longest-living trees: Japanese black pine. The problem I was investigating is noticeable as white masses on the needles and buds.
In their native environment — moist coastal areas of Japan and South Korea, and similar environments like the Pacific Northwest – Japanese black pines (Pinus thunbergii) can grow to about 100 feet tall. The few I have seen in gardens around Napa Valley are small and irregular in shape, but healthy. They tolerate many challenging conditions including dry sites, salt spray, soil salts, alkaline soil and acidic soil. A couple of things they do not tolerate well are poor drainage and excessive shade.
I can attest they hang on for dear life when pot-bound. I had 1 in a 15-gallon nursery container for about 20 years, intending to develop it as a bonsai. I just kept it in full sun exposure and watered it regularly, but I never got around to repotting and beginning its formal training. It refused to die but its growth gradually slowed down. Eventually, I found a good home for it with a local bonsai enthusiast who is now developing it into a styled specimen.
On the specimens I examined last week, I recognized the “white mess” as a sign of adelgids, also known as wooly aphids. I had seen it on pines long ago, and on other trees that are subject to similar insects. Various species are common on crabapples and some oak species. They have complicated life cycles that may include colonizing roots.
One of the main concerns about infestations in oaks is the sticky mess of the wooly material shedding on furniture and surfaces under and near the trees. They feed by sucking sap, so they are of some concern for tree health.
There is some confusion as to proper identification of species found on pines. Some references call them wooly aphids while other say “adelgid” is correct.
Short of sending samples to a lab for identification, a search through reference books and websites turned up a good probable identification. At Bugwood Wiki: Pineus strobi, the pine bark adelgid.
That website characterizes the insect as “one of the most serious insect pests of nursery, ornamental and landscape Eastern White Pine in Tennessee.” Infestations become so heavy that the bark appears as if coated with snow. Heavily infested young trees may “become discolored, stunted or weakened and death may occur”, the article says.
Here in Napa, we have no eastern white pines except, perhaps, for a few collector’s items in gardens, but we do have a few of the other susceptible pines including Austrian and Scots pines.
For control, the “Bugwood” article mentions dormant oil sprays before growth starts in spring. UC IPM online offers some recommendations for wooly aphids in general including insecticidal soap or “narrow range oil” solution applied at high pressure.
As trees and their associated pests now begin their period of rapid growth, this is a good time to get out there, have a close look for problems and nip them in the bud.
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