One of the most significant components to West Virginia’s forests is the yellow-poplar (Liriodendron tulipifera). Yellow-poplar is the largest tree in many forest stands, often reaching heights of 115 feet and diameters up to 36 inches. This tall, stately tree is one of the most important timber species of the central hardwood forest and provides substantial value to the wood products industry. Aside from its use in the wood products industry, yellow-poplar is also important to apiarists as its late spring flowers contain copious amounts of nectar.
The large size of a mature yellow-poplar generally causes many homeowners to be wary of allowing it to grow too closely to their homes. However, the tree is still widely used in landscapes, particularly larger area such as parks and campuses. The genetics of the species vary between individual trees and overall from region to region.
Overall, yellow-poplar is generally free from serious pests and diseases. A few insects that sometimes cause noticeable damage on yellow-poplar in West Virginia are the root collar borer (Euzophera ostricolorella), yellow-poplar weevil (Odontopus calceatus), and the tuliptree scale (Toumeyella liriodendra). This article provides an overview of the yellow-poplar weevil and the tuliptree scale.
For example, many sources will rate yellow-poplar as very susceptible to damage from loads of snow/ice and wind. However, in many areas, yellow-poplar is one of the most resilient species after a wind event or snow/ice storm. Indeed, there have been stands of mixed hardwoods where a tornado destroyed most of the trees, yet the yellow-poplars, though originally taller than most of the surrounding trees, remained standing. Granted, these yellow-poplars likely had severe ring shake, but at least some credit must be given them for withstanding such an event!
The yellow-poplar weevil is a beetle, a member of the Coleoptera insect order. It is native insect with a range that extends across much of the eastern and southeastern United States. While the preferred host is yellow-poplar, the insect also feeds on the leaves of other members of the Magnoliaceae family and sassafras. Although the damage can be quite noticeable and unsightly, it seldom causes healthy trees to decline or die.
Adult yellow-poplar weevils overwinter in organic materials on the ground. In mid spring, as new leaves emerge, they emerge from the materials on the ground, and begin to feed on new growth and leaves. Adult yellow-poplar weevils are often confused with various species of ticks. During late spring, female adults lay eggs inside the midribs of leaves. Tiny larvae emerge from the eggs and feed in between the layers of the leaves. The larvae are essentially leafminers at this stage and cause symptoms typical of a leafminer. Large areas of leaves become uniformly brown. However, at this stage, the tree doesn’t typically appear brown from a distance since most leaves are not infested.
As the season progresses, the larvae pupate between leaf layers inside mines where the larvae have fed. In a few weeks, typically around early to mid-June in West Virginia, adult yellow-poplar weevils emerge. There is generally a much larger number of adults present from eggs laid in the current season compared to the number of adults that overwinter and emerge the following spring. The adults that emerge during June from the current season eggs feed on leaves and cause conspicuous browning during years where yellow-poplar weevils are at high population levels. When viewed up close, the damage on leaves has a rice shaped area where the leaf tissue has been consumed. The adults that emerge in June feed on leaves until early to mid-July and then seek shelter in leaf litter and other organic matter beneath the tree where they remain between mid-July and emergence next spring.
Although the yellow-poplar weevil life cycle occurs every year, outbreaks are not guaranteed to occur every year. In fact, many years may pass in between outbreaks. As populations of yellow-poplar weevils reach high numbers, parasites begin to attack the weevils and cause their numbers to decrease. Although the damage caused by yellow-poplar weevil can be quite unsightly, it usually does not occur in consecutive years for a given location. Unless a yellow-poplar is quite stressed, the insects seldom cause decline or death. Stressed trees such as those having recent construction activity around their roots can be severely injured by this pest and either die or enter into a decline. Overall, the insect is not known to significantly impact a healthy forest ecosystem.
In a landscape setting, where the damage from yellow-poplar cannot be tolerated, systemic products that contain the active ingredients imidacloprid or dinotefuran may be applied to reduce the numbers of and damage caused by yellow-poplar weevils. It is important to keep in mind however that since yellow-poplar weevils are fairly mobile, a tree that is treated will likely still suffer some damage from weevils that fly in from adjacent untreated trees and feed before succumbing to the insecticides. The best approach is to realize that the damage is generally only apparent for one or a few successive years and allow the trees to recover on their own.
A less conspicuous but more serious pest of yellow-poplar is the tuliptree scale (Toumeyella liriodendra). Tuliptree scale can be problematic across habitats and stages of stand development. Tuliptree scale hosts include any member of the Magnolia family and serious outbreaks occasionally occur on yellow-poplar in West Virginia. The pest causes damage by sucking large quantities of sap from the plant, causing loss of vigor, and depending on severity of infestation, death. As is the case with many pests, yellow-poplars that are stressed from drought or other causes are generally more likely to experience decline and mortality from the tuliptree scale.
The tuliptree scale is native to the eastern United States. In West Virginia, there is one generation of tuliptree scale per year. Tuliptree scale females have eggs which hatch internally. A single female tuliptree scale insect produces thousands of offspring. Once hatched these first instar nymphs crawl from the female, and are referred to as crawlers. Both male and female crawlers are mobile and move around within and between trees. This life stage is the only time that the females are mobile. These tiny (around half of a millimeter) crawlers are active in late summer through fall. The nymphs then overwinter on the bark of twigs and branches. In spring, the females are stationary but grow much larger in size and eventually reach around a tenth of inch in size. Males pupate and grow as well but remain quite small in comparison to the females. The adult males are mobile with legs and two wings. In mid-June, the males mate with females, starting the life cycle over. Males die after mating and females die at the end of the growing season.
Signs that a stand of yellow-poplar is infested with tuliptree scale become quite apparent as the growing season commences. The scale produce copious amounts of frass that causes objects and plants beneath them to look wet and shiny. Eventually, black sooty mold grows on this frass and turns all items (including yellow-poplar foliage) black. Premature yellowing and leaf drop occurs. This leaf drop is likely due to a combination of the plant not having enough sap to maintain foliage and also a response to the reduced photosynthetic activity of foliage that is coated with frass and mold. Plants growing beneath the canopy of a yellow-poplar infested with scale suffer reduced vigor and death due to the coating of frass and mold. This can potentially be beneficial if the understory is primarily invasive species, such as Japanese stiltgrass (Microstegium vimineum). However, this is often not the case and instead forest regeneration is hampered.
In a landscape setting, tuliptree scale is generally effectively treated with systematic insecticides such as dinotefuran. However, this treatment is not typically feasible in a forested setting. Fortunately, there are natural enemies of tuliptree scale that generally keep it in check and reduce outbreaks to simply a year here and there. Although little can be done to reduce drought stress, other types of stress such as root disturbance, should be minimized. Residual yellow-poplar post timber harvest are also quite susceptible to outbreaks of tuliptree scale. Although these are often poor form yellow-poplar and are generally not of concern, an outbreak of scale on these residual trees can certainly impact regeneration in the stand.
Overall, yellow-poplar is one of our most resilient forest trees in West Virginia. Not even the spongy moth (Lymantria dispar) threatens this species. Thus, compared to many other of our forest trees, there is lesser amount of literature devoted to its management and health. However, we need to remind ourselves to not take the health of such an important tree in our forests for granted and monitor yellow-poplar for both existing threats and new ones that we might not be aware of yet. A little monitoring could go a long way in preserving the health of this important West Virginia timber, ecological, and landscape species we call both yellow-poplar and tuliptree.