Tuliptree scale—Toumeyella liriodendri
This introduced (exotic) sucking insect (Coccidae) is a serious pest in the San Francisco Bay Area on tulip tree, Liriodendron tulipifera, and on deciduous magnolias. Its other hosts include gardenia and linden.
Identification
Mature females are up to 1/3 inch long, irregularly hemispherical, and variably colored, usually brown or gray with irregular black blotches and markings of green, orange, pink, red, or yellow. Older females are more uniformly brown and resemble certain lecanium scales, Parthenolecanium spp. However, the lecanium females mature earlier and by late June are dead and dried out; female tuliptree scales are alive through the fall.
Male tuliptree scale nymphs mature into adults within gray to white, puparia (hardened skins of the older nymphs). Puparia are about 1/10 inch long, flat, and broadly oval. The delicate adult male has a red body and one pair of wings.
Crawlers (mobile first instars) are reddish. Settled first instars and early-second instars are about 1/24 inch long, oval, chocolate brown, and very difficult to see. Large colonies of tuliptree scale commonly have a distinctive, strong, musky odor.
Life cycle
Females mature in late spring and are alive throughout the summer and fall (they exude liquid when their body is squashed). Males develop into adults in spring, mate, live only a brief time as adults, and do not feed.
Adult females produce crawlers from August through November and give life birth to nymphs. First instars settle to feed on leaves and young twigs. Overwintering is as dark, second-instar nymphs on twigs. There is one generation per year.
Damage
The scales suck phloem sap and excrete copious, sticky honeydew, which results in blackish sooty mold growth and attracts ants. Heavy infestations weaken or kill young trees. Feeding on terminals can cause shoot dieback, leading to bushy regrowth. On older trees, feeding by prolonged high populations causes limb dieback and the decline and sometimes death of tulip trees.
Solutions
Control ants, which attack scale parasites and predators, interfering with biological pest control. If applying horticultural oil, spray overwintering nymphs during late winter (delayed-dormant season, as buds begin to swell) or spray foliage and shoot terminals during September or October, after most crawlers have emerged.
Applying a systemic insecticide is the most practical method for managing this difficult-to-control pest on large trees. Because systemic insecticides can move into nectar and pollen, to minimize toxicity to pollinators and natural enemies that visit flowers, make the application after plants have completed their seasonal flowering.
For more information, consult the Pest Notes: Scales and The Scale Insects of California Part 1: The Soft Scales. |
Adult female tuliptree scales
Females (left) male puparia (white, right)
Second instars overwintering
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