Recent woody ornamental insect and non-insect arthropod pests of interest seen in the UMass Extension Plant Diagnostic Lab:
Eastern Spruce Gall Adelgid: Adelges abietis is a pest on spruce, primarily Norway and white spruce. This insect is believed to have been introduced to North America from Europe prior to 1900. The insect causes galls to develop on shoots, which predisposes them to breakage under the weight of snow (although this has not been a problem this year) and other abiotic stresses. Unlike Cooley spruce gall adelgid (Adelges cooleyi), the eastern spruce gall adelgid will have branch growth beyond the gall (the gall is rarely terminal on the twig). This adelgid overwinters as a partially developed female who will lay 100-200 eggs, covered in a woolly material, around bud-break. After egg hatch, nymphs will feed at the base of needles, causing abnormal twig growth and a gall to form. Until the gall breaks open in mid-late summer, the young adelgids are protected from predators, parasites, and most abiotic stresses. Due to the protection this gall offers the insect, a dormant oil application just prior to bud-break is the best strategy for management, allowing the user to catch the eggs and newly emerged nymphs prior to feeding and gall formation. Avoid using dormant oil applications on cloudy and cold days and seek a time period to apply when temperatures will remain above freezing for 24-48 hours after application to avoid plant injury.
Honey Locust Spider Mite: Eotetranychus multidigituli is a pest on honey locust, Gleditsia triacanthos. This particular mite species is interesting in that it overwinters as adult females, shown in the photograph below. Although this image may look more like the surface of Mars, it is actually a close-up view of the adult females hiding in the crevice of the bark on a branch of honey locust. Eggs are laid in the spring. Light feeding can cause white or yellow stippling in the leaves. Heavy feeding can cause honey locust foliage to brown and die. Large overwintering populations can be treated with a dormant horticultural oil spray (Childs et al., 2008). Be sure to get as complete coverage in bark cracks and crevices as possible where these tiny red-colored mites are seen. Again, avoid using dormant oil applications on cloudy and cold days and seek a time period to apply when temperatures will remain above freezing for 24-48 hours after application to avoid plant injury. Especially if populations are low, avoid using other chemical pesticides for management as they may impact populations of beneficial, predatory mites which usually manage honey locust spider mite effectively.
Norway Spruce Gall Midge: Piceacecis abietiperda is a pest on Norway spruce, Picea abies. This pest was first reported in Orange, Connecticut in 1983 and is thought to originate from Europe. It has since been reported in Massachusetts, Vermont, New York, New Jersey, and New Hampshire. This insect is thought to have one generation per year in our area. Adult emergence in the Northeast is thought to occur in April and May. Soon after emergence, the males and females mate and eggs are laid on twigs near the bud or on new shoots. Larvae then hatch in approximately one week and burrow into tissue around bud scales, shoots, and terminal buds causing swelling. The image below is of one such larva, exposed by slicing through tissue swelling near a bud. Past studies have shown larvae to be fully grown in mid-September to October, with pupation occurring in early April. Some samples received at the UMass Plant Diagnostic Lab have shown small overwintering larvae. Norway spruce branches can exhibit browning and needle drop along with bending in the branch with the presence of galls on the inside of the bend. While some samples seen in New York and Connecticut have not shown enough damage to warrant management of this insect, other samples received by the UMass Plant Diagnostic Lab from western Massachusetts have shown significant dieback associated with the presence of this pest. Chemical management of gall midges needs further study and many chemical options in Massachusetts are not yet labeled for this pest. Spinosad is labelled for the management of “gall midges” in ornamental trees as a foliar treatment in both landscape and nursery settings, although exposed life stages would have to be targeted as contact of the pest is required when using spinosad. Other gall midges have been monitored for their emergence as adults with yellow sticky cards, so this technique may be able to be adopted for this pest as well.
Woody ornamental insect pests to consider for the beginning of the 2016 season, a selected few:
Eastern Tent Caterpillar: Malacosoma americanum is native to the United States and has been reported as early as 1646. Large numbers of the caterpillars of this species occur at intervals of approximately 10 years. It is a pest of cherry, apple, and crabapple as well as ash, birch, willow, maple, oak, poplar, and witch-hazel. This insect overwinters as an egg in masses of about 150-350 eggs which can be pruned from the branches of its host trees. Egg masses of Malacosoma americanum vary from those of Malacosoma disstria, the forest tent caterpillar, as they have a rounded edge whereas M. disstria egg masses have square edges. Monitoring for and pruning of egg masses should be done immediately, as we are fast approaching the time period where egg hatch will begin. Eggs will hatch as early as 50 Growing Degree Days in Massachusetts (50-400 GDD’s, base 50°F). Once cherry leaves begin to unfold, eggs will hatch and larvae will emerge. These larvae gather together in branch crotches and begin to spin a silken web over themselves. If caught early, these webs can be pruned out of the host trees mechanically and destroyed. DO NOT BURN these webs while they are in the host tree. Not only is this practice dangerous from a fire hazard perspective, but it may cause more damage to the tree than the caterpillars ever would. Large larvae of M. americanum are black with a white stripe down their back with a series of blue spots on either side. Larvae will find tree trunks, fences, and other objects to settle on and pupate in white cocoons. Adults will emerge in late June to early July and there is generally one generation per year. Avoiding damage early by removing egg masses and small webs is best, but for populations that are not prevented this way, caterpillars may be treated on warm days after bud break as they leave their webs to feed on foliage. Some chemical management options for M. americanum in MA include insecticidal soaps, spinosad, and Bacillus thuringiensis ‘Kurstaki’ which should be applied to target young caterpillars.
Elongate Hemlock Scale: Fiorinia externa is an armored scale that can be found on eastern, Carolina, and Japanese hemlock and also on yew, spruce, and Douglas fir and was first discovered in New York in 1908. This non-native pest can be found as adults attached to the underside of host needles. Females can be seen year-round and are covered in a brown, smooth waxy covering whereas males are seen mostly during the growing season and at some stages are covered in bright white, woolly material. Both sexes are less than 1/8 of an inch long. This insect is a serious pest in forested settings, especially when combined with hemlock woolly adelgid, but can also be found in landscape trees and hedges. The insect feeds by inserting long mouthparts into the needles of these plants and removing the liquids inside. Females can live for more than one year and will lay eggs under their waxy covers. Eggs will hatch and young nymphs known as crawlers act as the dispersing stage and will settle out on new needles. Long-range movement of these crawlers may be accomplished by wind. Crawlers can be present in May; however overlap of many developmental stages at any given time has been observed. Management options for this insect, as with all others, can include doing nothing. This may be desirable in a forested setting if the severity of the infestation is too high and the value of the trees too low. This option may also preserve genetic diversity, if any resistance is present. Highly infested landscape trees can be removed and chipped and covered or dried away from healthy trees and replaced, if this is an option. Chemical management options can include foliar applications of insecticidal soaps and horticultural oils, if complete coverage of the insect is able to be achieved (on smaller plants). These applications may be most effective if made while crawler stages are present and exposed (not covered by their waxy scale). Some systemic insecticides are available for the management of this insect on larger landscape specimens where complete coverage cannot be achieved, including dinotefuran which can be effective within weeks of application. Although this chemical is a neonicotinoid which are currently under review, hemlock is wind pollinated and poses a reduced risk to bees and other pollinators for that reason (there is no pollen or nectar that would be attractive to beneficial insects which may have traces of the systemic insecticide). Application can be done as a trunk injection, soil drench, or basal bark spray. Dinotefuran can also protect trees from hemlock woolly adelgid for about 2 years. Please note that imidacloprid does not manage elongate hemlock scale populations. It is also important to observe scales with a hand lens or under a microscope in subsequent years following implementing management strategies as the waxy scale covering can remain for long periods of time without a live insect present, thus not requiring further management. As with all chemical insecticides, use best management practices to reduce drift, avoid applications during times of day when pollinators are most active or when flowers are in bloom, reduce impacts to non-target organisms, and observe all regulations when applying near schools, wetlands, and other sensitive areas or populations.
Forest Tent Caterpillar: Malacosoma disstria is native to North America and is a pest on oak, birch, ash, maple, elm, poplar, and basswood. While referred to as a tent caterpillar, this species does not construct a tent like that of M. americanum. The forest tent caterpillar larvae create a silken mat on the trunk or branches of their host trees and will forage on one branch at a time. Caterpillars of this species are very similar to that of M. americanum, but can be differentiated by the white, “key-hole” shaped spots down their back.Larvae will pupate in pale yellow cocoons spun in folded leaves attached to vegetation or inanimate objects. Adults will emerge around the same time as M. americanum and lay eggs which will overwinter for the next season. There is generally one generation per year. Eggs are laid in masses on host branches and can be distinguished from M. americanum in that they have a squared-off edge. Egg hatch occurs between 192 and 400 GDD’s (base 50°F) in MA. Scouting for these egg masses should also be going on at this time so that masses can be pruned out of trees and destroyed. Because no web is formed with this species, the simplest option for mechanical control is during the egg stage. Chemical management options are similar for the forest tent caterpillar as those listed for the eastern tent caterpillar and include insecticidal soaps, spinosad, and Bacillus thuringiensis ‘Kurstaki’ and should also be applied to target young caterpillars.
Gypsy Moth: Lymantria dispar is an insect native to Europe but very well known to the Northeast. Introduced to 27 Myrtle Street in Medford, Massachusetts accidentally by Mr. Trouvelot while in search of a silk moth that would survive in the United States in the 1870’s, it has been a significant defoliator of forest and landscape trees in Massachusetts ever since. Host plant species include their favorite, the oaks, however this insect will feed on many other species including apple, alder, basswood, hawthorn, poplars, willows, elm, hickories, maple, and sassafras. The Massachusetts Department of Conservation and Recreation reports that gypsy moth was responsible for 38,175 acres of defoliation mapped aerially in Massachusetts in the 2015 season, particularly in the eastern part of the state and areas around the Quabbin Reservoir. Many report seeing increased numbers of egg masses, caterpillars, adults, and pupae of this insect last year. Egg masses are laid in groups of 100-600 or more and are covered in a dense coating of brown hairs from the female moths. Eggs can be laid on host plants, fences, lawn furniture, vehicles, etc. It is this life stage that overwinters and may provide us with a sizeable population of these moths again in the 2016 season. If present in low numbers, they may be mechanically removed at this time. Gypsy moth eggs will hatch around 90-731 GDD’s (base 50°F) in Massachusetts. Larvae will emerge around April to May and can be distinguished by their hairy appearance and five pairs of blue spots directly behind the head followed by six pairs of red spots to the end of the abdomen. Large enough larvae will find a sheltered place to pupate in a dark brown pupal case and adults will emerge around the middle of July. The female is flightless and will attract the male using pheromones. The increase in gypsy moth last year has been attributed to a dry and warm spring, conditions that are not favorable for the fungus, Entomophaga maimaiga which has been a significant factor in decreasing gypsy moth populations. For this reason, we should hope to have a wet spring to allow for the fungus to multiply and perhaps reduce the numbers of young gypsy moth caterpillars. An NPV virus also helps lead to crashes in the Lymantria dispar populations in Massachusetts. If you are living or working in an area that saw an increase in gypsy moth egg masses last year, you may be interested in management options in addition to waiting for the NPV virus and fungus to catch up to the population. Insecticidal soaps can be used on small caterpillars, as well as options such as spinosad and Bacillus thuringiensis ‘Kurstaki’.
Winter Moth: Operophtera brumata has been a significant defoliator, particularly in eastern Massachusetts for over a decade. It is a pest of oaks, maples, cherries, basswood, ash, certain species of elm, crabapples, apple, blueberry, and even some spruce and heathers in other countries. Originally thought to have come to Massachusetts from the population in Nova Scotia, Dr. Joe Elkinton and his lab are in the process of completing a study of the genetics of populations of winter moth from Massachusetts, Canada, and areas across Europe and have reason to believe our winter moth is genetically different from those in Nova Scotia. Winter moth continues to defoliate in eastern Massachusetts and has been observed by the Elkinton lab to be mixing (and even interbreeding!) with a very similar species, Bruce spanworm (Operophtera bruceata), on the western edge of the population. Bruce spanworm is very difficult to distinguish from winter moth using morphological identification techniques. The Massachusetts Department of Conservation and Recreation reports that winter moth was responsible for 61,924 acres of defoliation mapped aerially in Massachusetts in the 2015 season, particularly in the eastern part of the state mainly in counties such as Essex, Norfolk, Bristol, and Plymouth, along with pockets in Barnstable and Middlesex counties. For monitoring and management purposes, knowledge of the lifecycle of this insect (and other insect pests) is very important. Eggs are tiny and laid by female winter moth in the cracks and crevices of host plant bark in groups of 150-350 eggs per female (Faubert, 2016). Eggs should be orange-red in color at this time, but will be very quickly turning the light, powder-blue then dark blue color exhibited just prior to egg hatch. Using a base of 50°F when monitoring Growing Degree Days, winter moth egg hatch should occur around 20-50 GDD. Dr. Elkinton recommends monitoring Growing Degree Days beginning January 1st using a base of 40°F when trying to predict winter moth egg hatch as this threshold of 40°F is closer to the insect’s actual developmental threshold. If you are using the Network for Environment and Weather Applications (NEWA; http://newa.cornell.edu/index.php?page=degree-days) web site to monitor GDD’s with a base 40°F, Dr. Elkinton recommends expecting winter moth egg hatch to begin around 240 GDD accumulated from January 1. He estimates that the majority of winter moth egg hatch will occur early this year, perhaps by the end of March. However, this could happen earlier if we experience prolonged periods of warm temperatures, or be delayed if cooler temperatures prevail. If cool weather continues and egg hatch is delayed until April, Dr. Elkinton reports that fewer GDD’s are required for egg hatch. For example, in 2013 egg hatch occurred around April 15th at a mean GDD accumulation of 177, well below hatch observed at 240 GDD in 2012. As you can see, monitoring winter moth egg hatch this way is incredibly complex. There are reports that a few winter moth eggs are turning blue in Franklin, MA as of 3/16/2016, however the majority are still orange. Knowledge of when to expect egg hatch is important as chemical management options need to be applied at that time.
For information about winter moth management options in blueberry, visit: http://extension.umass.edu/fruitadvisor/sites/fruitadvisor/files/fact-sheets/pdf/Winter%20Moth%20Recommendations%20in%20Blueberry.pdf . For ornamental trees and shrubs, dormant oil can be applied to winter moth eggs just prior to hatch and followed with an application of spinosad at the time of hatch on young caterpillars. The timing of this application is critical as caterpillars must be reached before they wriggle into the buds of their host plants where they will be protected and begin their destructive feeding. Larvae will feed in the bud before it opens, then free-feed after trees leaf out through June. Larvae will then drop to the soil and pupate there. Please be aware that when moving soil from nearby host-plants or transplanting host trees of winter moth, you may be inadvertently moving winter moth pupae to a new location. Look for and remove any pupae in such soils from May through the fall. Adults will emerge in November through January and mate and the flightless females will lay their eggs again. To make monitoring of winter moth eggs easier next season, tree bands can be set up in mid-late October (emptying them throughout the adult flight season) which encourages female winter moths to deposit eggs above and (primarily) below the tree band. These eggs can then be monitored next spring for the color change indicating egg hatch. When managing winter moth, be aware that Dr. Elkinton and his students have released the parasitic fly, Cyzenis albicans, throughout eastern MA. They have had successful establishment of this biological control agent in Wellesley, MA and have been able to collect this fly from overwintering populations. Winter moth populations in Wellesley, MA seem to be decreasing as the numbers of this fly increase. Management of the winter moth should include the preservation and encouragement of beneficial insects, such as Cyzenis albicans.
For More Information About Pesticides and Pollinators:
Clemson University. 2012. How to Protect Honeybees from Pesticides: A Guide for Beekeepers and Applicators. http://www.clemson.edu/public/regulatory/pesticide_regulation/bulletins/bulletin_5_protecting_honeybees.pdf
Cowles. 2016. Neonicotinoids, Bees, and Urban Trees: The Controversy Defined. Urban Forestry Today Noonhour Webcast Series. https://vimeo.com/157623443
Mandy Bayer. 2015. Pollinators in the Landscape I: Importance of Pollinators and Causes of Decline. https://ag.umass.edu/fact-sheets/pollinators-in-landscape-i-importance-of-pollinators-causes-of-decline
Oregon State University. 2006. How to Reduce Bee Poisoning from Pesticides. https://www.cdfa.ca.gov/files/pdf/ReduceBeePesticideEffects.pdf
Report by Tawny Simisky, Extension Entomologist, UMass Extension Landscape, Nursery, & Urban Forestry Program