# The Slow Storm: Tree Mortality in CT from Invasive Insect Pests

By Thomas E. Worthley, UConn Associate Extension Professor, Forestry

During the early summer of 2018 it became apparent that numerous trees throughout eastern and southern Connecticut did not produce leaves this spring, having died sometime during the winter. While it is not unusual to lose a tree or two to natural causes here and there at any time of year, the massive scale and extent of oak tree (Quercus spp.)mortality during the winter of 2017 to 2018 due to the combination of recent gypsy moth (Lymantria dispar) infestations and associated drought conditions is notable and concerning. Combined with the anticipated loss of ash trees (Fraxinus spp.)in many areas due to the invasive emerald ash borer (Agrillus planipennis), which has been moving across Connecticut from where it was initially found in northern New Haven County, the sheer numbers of LARGE standing dead trees throughout the state presents what might best be described as a slow-moving environmental disaster.

Emerald ash borer first appeared in the Connecticut landscape in 2012 after a slow but relentless spread across the country and has been gradually decimating the ash population in Connecticut since that time. A long period of detection sampling and information dissemination has raised the awareness about this pest with professionals, elected officials and members of the public. We’ve known it was coming and in many ways arborists, foresters, town staffs, CT-DOT and utilities have been preparing for it.

The sheer degree and extent of oak tree mortality in southeastern Connecticut, on the other hand, was unexpected and has overwhelmed many homeowners, Tree Wardens, foresters and others.

Many adult citizens recall severe gypsy moth defoliations during the early 1980s. At that time the forest took on a winter-like appearance across a large portion of the state for a couple summers in a row as the population of gypsy moth caterpillars exploded into our vast oak forest canopy. The caterpillar population then crashed as quickly as it grew (due to caterpillar disease factors) and since that time fungal and viral diseases, among an assortment of other caterpillar predators, has kept the population in check. Those of us that take note would see only spot infestations in various locations since that time. During the 1980s, as expected, trees produced a second set of leaves each of those summers, and while there was some mortality, the severity was not as intense or as wide-spread.

Also, in some places an additional secondary mortality event is evident. Early and mid-season browning of leaves on individual trees that leafed-out and seemed fine this spring indicates that other pests or diseases are continuing to affect previously stressed trees. Among the factors that might be responsible are two-lined chestnut borer, a native pest, and armillaria fungus, also known as “shoestring” fungus.

The current problem is two-fold:

First, very large dead trees with wide spreading crowns are very numerous along some roadways in eastern Connecticut. These conditions seem quite variable. One can drive several miles along a local road and not see any dead trees and then pass a stretch that has as many as 30 or 40 dead trees per mile. Implications for public safety are apparent.

Second, there are forest stands throughout the affected area experiencing severe mortality rates. This author has been in stands ranging from a few more dead oaks than usual to as much as 80-90% canopy loss. And these are not necessarily the poor-growing, stressed and uncompetitive trees, but are often tall magnificent trees with large crowns that seemed most robust and healthy. Assessment efforts are underway to ascertain the degree and special extent of mortality in forest stands.

From a timber value standpoint the potential for severe economic loss for woodland owners is potentially staggering. The total volume of commercially valuable timber, standing dead, that might be salvaged is beyond the capacity of the timber industry to address it. From a public safety point of view, the numbers of dead trees that have the potential to ultimately impact roadways and power lines is well beyond the capacity of property owners, town budgets, CT-DOT and/or utilities to address.

Initial data from a random sampling of ninety miles of local roads in several towns from Sprague to Haddam has indicated an average of 18 dead roadside trees per mile, half of which can be categorized as high potential risk. This roadside tree mortality survey is continuing on more local roads in more towns. Additional survey data is being collected by a team from UConn.

High-potential-risk trees photographed in Higganum and Brooklyn, CT in mid-June, 2018. Photos: Tom Worthley

During roadside tree mortality surveys, a tree will have been characterized as high potential risk if it is a large tree, with slight to severe lean toward the road and/or with most of its limbs and branches over the road, such that if not removed, half or more of the mass of the tree will, over time, eventually drop in the road. A sampling of roads in East Haddam, for example, where mortality from both gypsy moth and emerald ash borer is occurring, indicated 134 such high-potential-risk trees on 21 miles of road (smaller, less-potentially risky trees are not included, but are much more numerous) for an average of about 6 problem trees per mile. At a cost of somewhere between $500.00 and$1000.00 per tree, just those 134 trees will cost upwards of $67,000, perhaps over$100,000 for removal. State data for local road mileage estimates 118 miles of local roadway in East Haddam, the problem dwarfs the \$25,000 annual budget the town allocates for tree issues. One or two or a half-dozen dead trees along roads in town might be “acceptable” risk, but if the sampling data is accurate and we estimate over 700 potentially problematic trees in town, it will (if not addressed) become downright risky to drive or walk in the community over the next few years.

Key are the phrases “potentially problematic” and “over the next few years”. Unlike ash trees, dead oak trees do not decay and disintegrate in a short period of time. The first heavy, wet snow will bring down small twigs and branches this winter, next summer, larger limbs and branches will decay and drop, a few at a time. Larger limbs and trunks of oak trees might retain some structural integrity for another 3 to 5 years, but eventually the root system will rot and, gravity being the law, the entire remainder of tree will topple in whichever direction it leans. The more severe the lean, the sooner it will happen. Liability for possible damage or injury, even a few years from now when gypsy moth is old news, is likely to rest with whoever owns or is responsible for the tree in question.

In July of 2018 two ad-hoc meetings were held by concerned stakeholders to exchange information and discuss roadside tree mortality. Attendees at these meetings included representatives from CT-DEEP, CT-DOT, Eversource, UConn, some town elected officials, CIRMA, Tree Wardens and members of the forestry and arboricultural communities. The discussion was wide-ranging and thorough. Major points of agreement amongst attendees included the following:

• Roadside tree mortality presents a serious potential public safety hazard.
• The scale and scope of the problem is beyond the capacity of CT-DOT, Eversource and many towns to address the issue.
• Time is of the essence. Dead trees are unpredictable and dangerous for tree workers and timber operators, and become more dangerous the longer they stand.
• Additional assessment data is essential, plans to continue that effort should be encouraged.
• Emergency funding and logistical support should be sought. Is FEMA an alternative?

Recommendations for homeowners and landowners with dead trees near boundary lines or roadways are to obtain the help of an arborist or qualified tree service as soon as possible. Dead trees are hazardous trees and the owners of hazardous trees can be liable for damage or injury they might cause. The sheer number of trees that need attention has made it difficult to contract with arborists, so be persistent, but also be careful about engaging inexperienced or unlicensed contractors. Check references. A listing of licensed arborists can be found at the web site of the Connecticut Tree Protective Association, www.CTPA.org.

Woodland owners are advised to consult with a Connecticut Certified Forester about the condition of trees on their properties. Recommendations for management actions will vary depending on morality severity and size of that affected area. A listing of Foresters can be found at the CT-DEEP Forestry Division web page. Look for the “Certified Forest Practitioners” listing. Text within the document explains the roles and authorizations for different levels of certification, and is important to note. Landowners should be aware, however, that trees can lose some commercial value once they have died, and that stands with numerous dead trees to harvest are likely to be extremely dangerous to work, again potentially affecting value. Please do not attempt to remove or harvest dead trees on your own without proper personal protective equipment (hardhat, eye and ear protection, chaps) and some chain saw safety training.

Woodland owners with specific questions can contact me at thomas.worthley@uconn.edu.

Severe canopy loss/oak mortality at Beaver Brook State Park in Chaplin – mid June 2018

# Understanding Gypsy Moth Outbreaks

Gypsy moths (also known as the North American Gypsy Moth or the European Gypsy Moth) were imported to North America from Eurasia in 1869 for a silk production experiment. They have caused periodic defoliations in New England since then and particularly severe defoliations in the early 1980s and again in Connecticut and Massachusetts in 2016 and 2017. (Gypsy moths do not build webs – the webs you see in cherry trees are tent caterpillars.)

Female moths lay between 500 and 1,000 eggs that overwinter until spring when they hatch. Eggs are usually found underneath the bark scales of trees, on trunks, branches or other protected sites. Eggs last for 8-9 months before they hatch. Adults only live for about one week while they mate and lay eggs. Gypsy moth populations can persist with very low numbers for years but under the right conditions can have outbreak years where populations explode.

The caterpillars feed on leaves of most deciduous trees and many conifers as well. After feeding for some time they descend to the ground by means of silk threads to change size (molt). Silk threads and numerous hairs on the bodies of small, early-instar (stage) caterpillars allow them to be spread by the wind. These caterpillars change size three times before entering the pupal stage and maturity.

Gypsy moths only damage trees during the larval (caterpillar) stage when they are feeding on the leaves, and leaf-feeding and defoliation is the only type of damage they do. In high numbers they can completely defoliate the trees. One gypsy moth caterpillar can eat as much as eleven square feet of leaf area.

Most deciduous trees have the ability to re-set buds and produce a second set of leaves following defoliation.

Coniferous trees do not have this ability. Multiple defoliations can be problematic for the trees. Gypsy moth caterpillars will feed on most tree and shrub species (500 total species!) but prefer oak and beech. Tulip trees (yellow poplar) are not affected. Pines and hemlocks are likely to die after one defoliation.

Multiple defoliations combined with drought are causing individual tree and stand-level mortality in some areas. Trees that have not “leafed-out” in 2018 can be seen in numerous locations around the state. In some places, large individual roadside trees and trees near structures that have died present potential future safety hazards. In forest stands on state and private forest lands, sufficient oak mortality can be observed to warrant consideration of forest harvesting activities to salvage timber value. Private woodland owners are well advised to consult with a CT-Certified Forester to evaluate their woodland conditions. (Links provided below.)

Since the 1980s, a fungus from Japan, Entomophaga maimaiga, has been keeping gypsy moth populations under control but during dry conditions the fungus is less active. Gypsy moth populations seem to explode when there are dry conditions during the spring and summer months.

Natural controls include:

• Birds (limited effectiveness, small instars only)
• Vertebrates (deer mice and shrews)
• Invertebrates (ants and ground beetles, parasitic flies and wasps)
• Viral Disease Wilt
• Pathogens like Entomophaga maimaiga fungus

There are a few management tools available:

• Bacteria-based treatments exists.
• Soapy water sprays (horticulture soap/oils mixed with water).
• Finding and destroying egg masses (too late for 2018).

Pesticides are not commonly used because of chemical toxicity and are impractical for entire forests. If used for an individual tree be sure to read the label.

On the UConn campus in Storrs the arborist crew will spray some campus trees using bio-based spray. Trees that don’t leaf out will be removed. Some salvage of dead trees in the UConn Forest will take place as appropriate for fuel wood and saw logs. Inspections will be done in early summer.

A Certified Forester should be consulted for stand-level management and a licensed arborist for individual trees near homes and buildings. More information is available from the Department of Energy and Environmental Protection: http://www.ct.gov/deep/cwp/view.asp?a=2697&q=589362&deepNav_GID=163 and the Connecticut Agricultural Experiment Station; http://www.ct.gov/caes/site/default.asp .

To find an arborist link to the CT Tree Protective Association, www.ctpa.org.

Article by Tom Worthley

# Gypsy Moth Caterpillar Update

From Extension Educator Tom Worthley:

“The attached photo is of a 26-inch diameter oak near my home with lots of caterpillars on it, and all of the caterpillars are dead. They exhibit symptoms of the fungus that attacks gypsy moth caterpillars, particularly when populations are high. So while I cannot say it with absolute certainty, I am of the opinion that the Entomophaga maimaiga fungus is at work (finally). Dry spring seasons the last couple years had a depressing effect on the fungal activity, leading to the caterpillar outbreaks we are seeing this year, but we’ve had a wetter spring and while the defoliation ‘damage has been done’ in many areas (almost total defoliation in my area, Higganum) we are now seeing increased fugal activity killing off the caterpillars.

Most trees will re-foliate. This requires some drawing upon stored reserves of carbohydrates by the individual tree, in order to send out new leaves and the evidence of gypsy moth activity will likely appear as reduced diameter growth. Some trees that have been stressed by repeated defoliations in multiple years and perhaps by drought or other issues, might not survive. We will know in the next few weeks.
We will also know later this summer whether many gypsy moth caterpillars have survived to maturity. Non-flying, mostly white females will take up positions in sheltered spots on the bark of trees, and males (more tan, or buff-colored) will by flying around seemingly at random.”
Extension Educator Donna Ellis adds: “As the caterpillars decompose, the fungus reproduces inside the cadavers and on the ground around the trees.  Entomophaga will further spread in the area and can persist in the soil for many years. We recommend that property owners leave the caterpillars in place on the trees to allow the fungus to continue to develop and spread naturally. It remains to be seen how successful the fungus will be in reducing future gypsy moth populations, but hopefully it will have an impact.”