Tulip poplars, Liriodendron tulipifera, can be good fast growing trees in some urban
situations. They frequently come up as volunteers so you probably have them whether you like it or not. Tulip poplars are also very good nectar sources for honey bees and native bees. This shows how urban trees can perform multiple functions, including conservation. Concern for bees may lead more people to plant tulip poplars in the coming years so here is a primer on the major pests to watch out for.
A great thing about tulip poplars is that they only have two main pests: tulip poplar aphids and tulip poplar scale. The names are easy to remember. Unfortunately, both are copious honeydew producers. Thus, many tulip poplars and the ground, cars, patios, and slow dogs below them get covered in sticky honeydew and black sooty mold. This is the primary reason for citizen complaints related to tulip poplars and many other tree species.
Tulip poplar aphids, Illinoia liriodendri, are the only aphid typically found on tulip poplar. They overwinter as eggs in crevices around buds and become active in late spring. You can find them by late April in Raleigh. To scout for tulip poplar aphids just walk under a tulip poplar tree and look up. The first things you will see are small yellow aphids feeding on the undersides of the leaves. You may have a couple per leave or a couple hundred per leaf. The second thing you will notice is that you should have worn safety glasses because your eyes are stinging from drops of honeydew. The third thing though is that there may be a lot of natural enemies present on the leaves with the aphids.
Tulip poplar aphids become active before many natural enemies become abundant in the landscape each spring. In addition, many natural enemies, like ladybeetles, are attracted to aphids and won’t lay eggs if aphids aren’t present. Other natural enemies, like parasitoid wasps, lay their eggs inside aphids so of course would not be present without their hosts. Thus, some aphids need to be present before natural enemies find them and start to accumulate. Then the aphids typically crash as ladybeetles, green lacewing larvae, minute pirate bugs, parasitoids, syrphid flies, and other natural enemies go to work on them. Ideally, and in many landscapes, this is it; the aphids and natural enemies exist at low
levels throughout the summer and there is never a problem.
In other cases, particularly it seems in parking lots and near streets, the aphids go berserk. For whatever reason the natural enemies can’t keep up with them. This could be because the aphids are warmer and reproducing quicker or because natural enemies are not abundant in these stressful habitats, or both.
Tuliptree scales (Toumeyella liriodendri) feed primarily on tulip poplar though it is occasionally found on other trees including Magnolia spp. It occurs throughout the eastern US from New England to Florida. Tulip tree scales live on twigs. Nymphs and adults are gray or orange to brown. In August, adults swell to produce large brown hemispherical ovisacs. The scales overwinter as nymphs on twigs. In spring and
summer they feed heavily producing lots of honeydew. In late summer honeydew production declines as female scales begin producing eggs and crawlers.
Tulip tree aphids discolor leaves where they feed and produce honeydew but overall are probably not too bad for tree health at reasonable abundances. Tulip tree scales, however, can kill central leaders of young trees resulting in bushy plants with co-dominant leaders. Like other soft scales, they feed on phloem which is the sugary solution produced by photosynthesis in the leaves. By re