Soft scales of spruce and pine

Spruce bud and pine tortoise scales can produce lots of “honeydew” that allows black sooty mold to grow, possibly making trees unharvestable.

Spruce bud scale. Photo credit: Steven Katovich, USDA Forest Service,
Spruce bud scale. Photo credit: Steven Katovich, USDA Forest Service,

Spruce bud scale

During the week of June 8-14, 2014, we found numerous spruce bud scale (Physokermes piceae) on Norway, Colorado and white spruce. Spruce bud scale may often go unnoticed since their size and color can cause them to be mistaken for buds. They are round, reddish-brown in color and are often clustered in groups of three to eight at the base of new shoots. Often, populations become noticeable because the trees become coated with “glistening” honeydew. Lower branches are more often attacked than higher branches. Severe infestations can produce lots of honeydew that will allow sooty mold to grow.

On trees that are already weak or stressed, severe infestations may cause lower branches to die. There is only one generation per growing season. Young females overwinter on the underside of the needles. In the spring, females move onto the twigs to complete their development. Usually we see eggs hatch and tiny crawlers move around the twigs and branches in June or early July, or 700 to 1,150 growing degree days (GDD) base 50. Growers should be checking fields now. As with other scale insects, wait to apply treatments until you find the crawlers are active.

Pine tortoise and striped pine scales

Pine tortoise (Toumeyella parvicornis) adult female scales are reddish-brown whereas striped pine scale (Toumeyella pini) is similar in appearance, but has distinctive white stripes. For many years, both of these soft scales on Scots pine were called tortoise scale, but a scale expert finally made separation of the two species in the mid-1990s.

Michigan State University Extension suspects that you will find both active in many Scots pine fields that are heavily infested. What does this mean? Probably nothing to a grower since the biology and control of the two species are quite similar with a single generation each year. Also, there doesn’t appear to be much difference in timing of crawler emergence.

If you have Scots pine trees with moderate or high populations of scale, you need to start scouting your trees now. Both of these scales that feed on the woody part of pine shoots and small branches excrete amazing amounts of sugary honeydew. Black sooty mold then grows on the honeydew that coats the needles and branches. Trees can look pretty awful if the scale population builds up to even moderate levels. The black sooty mold seldom comes off the needles, even if you spray them with a power washer. Usually growers have to wait for two years or so until the affected needles are shed before they can sell these trees.

Pine tortoise scale Crawlers emerge
(Left) Pine tortoise scale on branch. (Right) Crawlers emerging from pine tortoise scale. Photo credits: Jill O'Donnell, MSU Extension

Pine tortoise scale eggs usually begin to hatch around 400 to 500 GDD50 and stripe pine scale at 750-800 GDD50. The crawlers are pinkish-red and can easily be seen moving about on the shoots and needles. What has been difficult for growers to try and control these scales is that the eggs hatch over a relatively long period of time, continuing through 1,000 to 1,200 GDD50 (end of egg hatch and the last of the crawlers). Also, coverage is usually an issue. Often we find populations in the “shadow” areas where the pesticide doesn’t reach or penetrate the foliage.

Horticultural oil might be something to consider, especially if you can apply the oil after the crawlers settle and begin to feed. The oil will suffocate and kill the crawlers, but will have much less effect on the ladybird beetles.

If you choose to use a conventional insecticide, choose a product with some systemic activity or a longer residual. Whether you use horticultural oil or a conventional insecticide, be sure to get good coverage!

While you are scouting, keep an eye out for white, fuzzy insects that look like little mealy bugs. These little white insects are actually larvae of a ladybird beetle in the genus Hyperaspis. This species of ladybird beetles specializes on pine tortoise scale. The adults and larval ladybugs will eat the scale eggs and crawlers. At this time of the year, the ladybird beetle larvae will be very small. They may even crawl up and hide under the female scales on the needles. Once the eggs are laid, the Hyperaspis larvae will feed aggressively on the eggs and then on the crawlers. They will get larger over the next few weeks and you will probably see them on the infested shoots and branches. These ladybird beetles can be pretty amazing. We have seen a number of fields where this ladybird beetle controlled even heavy tortoise scale infestations in a single summer.

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