In this Issue:
- Black pineleaf scale: crawlers begin hatching in about a week
- European elm scale: crawlers begin hatching in a few days
- Ips bark beetles: the most common urban bark beetle pest
Black Pineleaf Scale
Crawlers begin activity June 13 – 21 along the Wasatch Front
Black pineleaf scale affects Austrian, Scotch, and mugo pines. If trees are to be treated with a foliar application (instead of spring-applied systemic), it should be applied by June 13 (warmer areas of Wasatch Front) or June 18 (cooler areas). By mid-July, crawlers will have settled to immobility for the remainder of their lives, and treatment will be too late. Examples of more specific dates are:
- Kaysville, Linden (Orem), Provo Airport – June 21
- Pleasant Grove, Syracuse – June 15
- Pleasant View – June 19
- Riverton, SLS (Univ Utah) – June 18
- SLC Airport – June 13
The black pineleaf scale is an armored scale, concealing its body under a thick waxy covering. This scale feeds on nutrients and contents of mesophyll cells, and unlike soft scales, does not produce honeydew.
Where it feeds, needles becomes yellow with localized necrosis (death). Under heavy and prolonged infestations, needles that are normally retained for 5 years will drop in 1 to 2 years. New needles are sparse, stunted, and chlorotic. Branches die back and the tree may eventually be killed.
Treatment
Trees under stress from drought conditions or nutrient deficiencies are more susceptible to infestation, so remedy these conditions.
A systemic insecticide application (soil drench or lower trunk spray) can be highly effective, but is more expensive than foliar applications. The systemic should be applied in spring, while a foliar application must be timed with crawler emergence. In light infestations, two sprays of horticultural oil (1-2%), one week apart during crawler stage, could be all that is needed. Usually a professional applicator is needed for larger trees and/or high infestations.
- Residential: Organic options are horticultural oil (1%) or insecticidal soap, and conventional options are GardenTech Sevin (zeta-cypermethrin), or BioAdvanced Insect Killer (cyfluthrin).
- Commercial: Carbaryl, cyfluthrin (Tempo), Movento, dinotefuran (Safari) as a foliar spray
European Elm Scale
Crawlers begin activity June 13 – 16 along the Wasatch Front
European elm scale crawlers will begin activity along the Wasatch Front area in the next few days in warmer areas to next Monday in cooler areas. All elm species are hosts, including native American elms and all its cultivars, camperdown elm, and Siberian elm. It may rarely be found on the elm relative, zelkova.
This is a soft scale that produces honeydew as it feeds. This sticky material drips down onto cars, people, and other plants, which can be a nuisance. Branches and bark covered in black sooty mold (that thrives on the honeydew) is a sure sign of a heavy infestation. In addition, leaf yellowing, leaf drop, branch dieback, and loss of tree vigor can occur.
Females lay hundreds of eggs in early summer, and the eggs hatch into “crawlers” starting in early to mid-June and continue for approximately 4 weeks. Crawlers move to the underside of leaves and succulent twigs to feed for the summer, and then migrate back to twig bark and crevices for the remainder of their lives. There is a single generation per year.
Treatment
Scale insects are difficult to treat, but there are a few windows of opportunity for control. Since this scale is a sap-feeding insect, a systemic could be applied in spring (now is too late), such as one with the ingredient imidacloprid, dinotefuran, or orthene.
For targeting the insect without systemics, the first line of defense is a dormant oil spray in early spring. It will smother many overwintering soft scales. And then for severe infestations, target the crawler stage (now) because nymphs are more susceptible to treatment than adults.
- Residential: Horticultural oil (1%; in temps below 85°F on non-drought-stressed trees) or insecticidal soap, or if you can find it, a product containing azadirachtin are all organic options. Otherwise, Spectracide Triazicide, GardenTech Sevin, or Hi Yield Farm and Garden Insect Control.
- Commercial: horticultural oil, insecticidal soap, or azadirachtin are organic options. Conventional options are carbaryl, a synthetic pyrethroid, malathion, imidacloprid (foliar spray), acetamiprid, or dinotefuran (foliar).
Ips Bark Beetles
Keep conifers healthy and well-watered this summer
It is starting off to be a hot and dry summer, which is not good for many of our conifers. Conifers that are under stress are “attractive” to bark beetles.
The most common bark beetle in Utah’s urban conifers is the engraver beetle, also known as Ips. There are several species of ips beetles that attack conifers, primarily pines and spruces. The adults are tiny black beetles that are attracted to certain chemicals that the host trees exude.
Adult females bore into the bark of host trees and create a egg gallery in the inner bark, and lay eggs along that gallery. Larvae that hatch tunnel along the inner bark laterally, creating characteristic feeding galleries that prevent the flow of nutrients. Most ips beetles prefer to feed on smaller-diameter wood, which is why we often see the tops of trees dying first. Once the population builds locally, the ips will attack any size tree.
Treatment
As mentioned, the beetles are attracted to stressed or wounded trees, so keep your conifers as healthy as possible this summer to provide the best measure of defense.
- Prune trees properly and dispose of debris or any fresh-cut trees.
- Water as needed. Spruce trees are very shallow-rooted and are more susceptible to changes in water moisture.
- Prevent soil compaction.
- Avoid root damage.
- If needed, insecticide options are a trunk spray (from top to bottom) with carbaryl or a pyrethroid in early spring, late spring, and mid summer. The only systemic that has shown efficacy against bark beetles is emamectin benzoate, which is applied by a professional as an injection, providing two years of protection.