Blue spruce disease

Asked April 13, 2019, 6:54 PM EDT

We have 3 20 ft. Blue spruce in our yard. Last spring I noticed the white "bumps" on the needles. The infected needles start on the inside and bottom of the tree and work their way up and out. I sprayed the trees all summer with a fungicide at 2-3 week intervals and I thought that it slowed the disease but now this spring it seems to be very active again. We live at high altitude with desert like weather...any help would be greatly appreciated!

Saguache County Colorado tree health horticulture

1 Response

Based on the photos it looks to me like pine needle scale. I would imagine that you saw what appeared to be some relief from the fungicide application because the continual wetting (spraying every 2-3 weeks) had an affect on the insects, but the actual chemical you used has a different target (fungus, not insect) and so that wasn't doing anything. This is why it's important to get a proper ID of the disease or pest before applying pesticide. Moving forward you will be able to adjust your treatment accordingly. Also, you mentioned you live at high elevation and pine needle scale typically only has one life cycle at higher elevations. At lower elevations they will have two.

Here is select info from our fact sheet and a link to the full publication is below:

"During outbreaks, needles may be nearly covered with the bodies of the scales, giving an appearance that the plant is spattered with white paint. Heavily infested needles drop prematurely. Sustained outbreaks cause needle loss and sometimes twig dieback.

Additionally, egg hatch dates vary with elevation and seasonal temperatures. An early hatch, sometimes beginning in late April, can occur following periods of warm weather in late winter and early spring. Under cooler conditions, initial egg hatch can be delayed until as late as the first week of June. If cooler weather persists all spring, hatching can continue for a month or more.

Pine Needle Scale Control

Several natural enemies are associated with pine needle scale colonies in Colorado. A minute lady beetle (Coccidophilus atronitens) is commonly found feeding on eggs and developing scales in the spring and summer. Several species of chalcid (parasitic) wasps also are common. To see if these beneficial insects are present, examinine the white, waxy cover of the scale. Parasitic wasps produce small, round emergence holes near the center of the cover. Predatory lady beetles chew more irregular holes. Unfortunately, natural enemies of pine needle scale are not always sufficient to prevent damaging outbreaks.

Pine needle scale is more readily controlled with horticultural oils than are some other armored scales, such as oystershell scale. Oils applied during the dormant season (dormant oils) are recommended for pines. Spruce may temporarily discolor at the rates used for these treatments (about 2 percent concentration). Alternatively, oils that can be used during
the growing season can be very effective. These summer oil applications can kill young, settled scales, as well as crawlers and eggs. Do not apply horticultural oils when new growth emerges or if plants are under stress from drought. Summer applications also can discolor spruce.

Often, the most effective controls of pine needle scale are “crawler sprays,” insecticides applied to coincide with the vulnerable crawler stage of the insect. Many yard and garden insecticides are labeled for this purpose, including insecticidal soaps, Sevin, Permethrin, Orthene, cyfluthrin and various oils.

Apply crawler sprays shortly after egg hatch, which can be determined by monitoring. The small, rosy-colored crawlers are detected by shaking a branch over a piece of white paper. Try this survey when crawlers are expected to first appear, from late April to late May. If egg laying and crawler activity occurs over a period of several weeks, repeat applications of insecticides, particularly if short-lived residual treatments (soaps, oils) are used. To conserve natural enemies, avoid insecticides at other times in the life cycle of the scale.

On many plants, infestations are localized and can be controlled with spot sprays."