Despite their miniscule size, pine scale is actually classified as an insect. They are in the order hemiptera. This alone will tell us a great deal about the scale as insects in the hemiptera are the ones that have developed piercing and sucking mouthparts.
Unfortunately there are a number of plants that can act as a host for pine scale. We have found it to be very common in pine, obviously, but specifically Austrian, Scotch and the ornamental mugo varieties. Spruce, fir, Douglas fir and eastern red cedar are also known to be susceptible to this pest. The level of infestation will actually depend more on the overall health of a particular plant than anything else. A tree that is already weakened by drought stress, a nutrient deficiency, or mechanical injury will make a potential host tree a more ideal target than one that is up to full strength.
Pine scale will generally overwinter as an egg underneath their protective shell. When they will hatch is more closely tied to the weather than it is to the date on the calendar. Shockingly they have no consideration to our meticulous calendar system of days/ weeks. They can start to hatch anytime from late May to late-July. It will all depend on how cool or wet the spring/ early summer happens to be that year. Any days less than 50 degrees won’t count towards the development of the “crawlers”.
Once the needed number of warm days have come and gone the pine scale will hatch and come out as incredibly tiny (but visible) orange to reddish crawlers. These crawlers will then move around for a few days before settling down and starting to feed. They are most likely to settle down on the current year’s tender new growth.
Feeding will trigger the next change as they will start to yellow and become more visible withing a few days of insertion. After about 7 days they will then molt and enter what is called the hyaline stage.
The hyaline stage is the beginning of the end because in just 3-7 days after entering this stage they will begin to excrete the waxy material that forms their “armor”. We call it armor because it is very effective in protecting the scale from weather, pests and pesticides. Once that armor has formed the pine scale will stay underneath it until they start the cycle all over again next spring.
Damage starts as a small yellow spot around each of the individual scale insects insertion points. These spots will then coalesce to create an overall yellowing and then browning of whole needles and then branches. A severe case of pine scale will have a flocked look to the outer needles and a thinning of the older needles on the trees interior.
Pine scale is a little bit like an immunodeficiency disorder, it isn’t necessarily the first problem that kills you it is the second one that came because your immune system was compromised by the first. Aka pine scale weakens a tree by removing nutrients in the form of sap and by then causing enough needles to drop that the tree loses the ability to replace those nutrients.
Treatment, whether by pesticide or soap or oil needs to happen during the 1-3 week vulnerable period between egg hatch and the development of the waxy armor. Deciding what treatment is necessary will depend on: the importance of the tree, the level of infestation in the tree, the risk of spreading it to other high value hosts etc.
The market has a number of treatment options that range from dormant oils, introducing natural predators into your landscape as well as pesticides and insecticidal soaps. Each type of treatment comes with its own pros and cons. A dormant oil will cause a discoloration on blue spruce but will not harm any beneficials, aka natural predators or fly by insects. Introducing natural predators has the benefit of being worry free of off target effects but there is no way to ensure that those predators will stay on your tree or even your property. Insecticides can be very effective but can cause undo harm to other insects if they are not applied while properly following all label instructions.
There are several natural predators that will be able to keep a reasonable pine scale infestation in check. These include, multiple varieties of ladybird beetles (especially their larvae) as well as a parasitic wasp. If you see a clean hole poked into the white armor that is the sign of the wasp whereas a slightly larger and more irregular hole is the work of the ladybird beetle and its young. The ideal type of control would be to use a full IPM strategy. This means to strengthen the overall health of the tree, allow the natural predators to do their work and treat only what needs to be treated if something more direct is needed. The days of simply blanket treating an entire property with any chemical we have on hand is ending and we say “It can’t happen fast enough!”.
I have added some links and references to what I have used to write this blog down below if you would like to research pine scale on your own. Of course if you think you may have scale or are seeing something else in your landscape that you have questions about, feel free to give us a call at 208-523-5296.