European Elm Scale (EES) is normally a secondary pest of fruit and ornamental trees. This is the abbreviation we use throughout the text.
There is one generation of this insect a year in Calgary, with overwintering nymphs breaking diapauses in late May or early June. Shortly following this, the nymphs become adults and egg production begins about mid-June. Females produce eggs for most of their adult life. The egg-producing period lasts at least six weeks and several hundred eggs may be produced by each egg-laying female during this period. Eggs begin to hatch about late June or early July, and the first nymph stage is known as the crawler stage. Crawlers are minute (2-3 mm), quite mobile and are capable of dispersing several metres. The duration of the crawler stage is one to two weeks. However since females are producing eggs for most of the season, crawlers are encountered for about six to eight weeks with peak numbers occurring around mid-July.
By mid-July in Calgary, EES crawlers have moved to temporary feeding sites on the leaves of the host plant. The mouthpart, or beak, is not hard enough to penetrate harder plant tissues. As a result, crawlers start development on leaf tissues, seeking a protective niche within the crevice beneath the leaf mid-vein or larger veins.
Beginning in late August or the first week of September in Calgary and continuing throughout the month, nymphs migrate off of the leaves to overwintering sites on the twigs and branches. Nymphs overwinter in masses and are forced to initiate overwintering prior to leaf-drop or early frost regimes.
ArborCare recommends use of three opportunities to exert control on EES populations. The first is early spring with an application of horticultural oil; the second, between leaf emergence and June 30th, is a systemic insecticide injection for season-long control; and third, another horticultural oil spray in the fall if necessary.
Other forms of scale can be controlled through early season horticultural oil applications followed with Trounce® sprays during the crawling stages. Contact us today.