photo tcc
If you find your arborvitae looking sickly and covered in black sticky scale, chances are you have Fletcher Scale, Parthenolecanium fletcheri. This soft scale attacks a variety of hosts cedars, arborvitae, yews, hemlocks, and occasionally junipers.
The most commonly seen
stage of this insect’s life cycle is the female, who forms an almost
hemispherical tan/brown protective scale where she is attached to the stem of
the host tree or shrub. It is from this protective cover that she inserts her
moth parts in to the phloem of the plant and dines on carbohydrate rich sap.
This sugar rich diet results in the scale secreting the excess carbohydrate as sticky
honey dew that coats the foliage below the scales. This sugar is then attacked
by a sooty mold that turns the foliage black. If the infestation is severe the
plant will turn yellow and will lose foliage.
Females are the
only known sex that these scales exhibit. Reproduction is by parthenogenesis, without
sex.
The female lays as
many as 600 eggs in May and these will hatch in June, into crawlers that move a
short distance to a feeding site. They remain in this feeding site as a second
instar nymph, (developmental stage) until next spring when they rapidly develop
into mature females.
Control of this
pest is not difficult if your timing is perfect. Treating early in the year
with appropriate dormant oil reduces the number of overwintering second instar
nymphs. Verdant oil or registered chemical control must be applied when the
crawlers are active and exposed. Typically this occurs early June to early
July.
Because timing
varies due to climate, when Japanese tree lilac, or little leaf linden are
blooming, you are a week ahead of crawler hatch. Another simple way to
determine crawler emergence is to take several infested branches from your
plant, put them in a well-sealed zipper bag and put it on your desk or shelf
out of the sun. Check the bag daily and when the foliage appears to have fine
orange dust or speck on it they have hatched. Again you will be a week ahead of
the hatch in the outdoors as your office should be warmer than the woods.
I.S.A Certified Arborists
are industry recognized experts in plant insect and diseases control. Contact
your I.S.A. Certified Arborist to see if you have this damaging plant pest.
