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Invasive pests attacking Marylands forests - January 16, 2014

Trees, like all living organisms, are susceptible to diseases, pests, blights, parasites and other problems. While some of these issues are not life threatening, some can cause serious damage to the tree leading to death or an infestation that kills entire stands. In Maryland, we have had numerous pests, diseases, blights and other factors that have drastically changed our native tree populations and the make up of forests statewide.

 

Many of the pest and nuisance species that prey on trees in Maryland are invasive species, making their way to our local forests from infected nurseries and plants brought back to the mid-Atlantic states. Out of all the pest and nuisance species found in Maryland the gypsy moth is by far the most destructive pest of forest and shade trees. The caterpillars eat the leaves of oaks and other hardwoods in spring, mostly May and June, and if the infestation is heavy enough than the tree can be eaten bare or have only a few remaining leaves. Heavily defoliated trees may refoliate, but are still weakened, especially if defoliation occurs again in continuous years. Weakened trees are more vulnerable to other forest pests, diseases, drought and other stresses, and may die. Large outbreaks of gypsy moth caterpillars have affected hundreds of thousands of acres of trees statewide leading to the Maryland Department of Agriculture (MDA) conducting an Integrated Pest Management program for the gypsy moth to minimize unnecessary losses as the result, through monitoring, assessment, education, and pest control actions.

 

MDA personnel monitor the presence and severity of gypsy moth infestations using different surveys, but the most important are surveys of gypsy moth egg masses. Information from these surveys are used to assess the potential for damage and tree loss in each area, and is provided to landowners, managers and the general public so individuals and groups can make informed decisions about these infestations.

 

The gypsy moth, just like the trees they feed on, can be attacked by predators, parasites, and, most importantly, diseases. While these sources of mortality are monitored by MDA personnel, if these natural controls have not suppressed the populations, very high infestations may need to be treated with insecticide to protect trees in areas where dieback or mortality can not be tolerated. Two other major pests that can cause serious damage to forested ecosystems, trees, and even farmers is the Southern Pine Beetle and the Pine Shoot Beetle.

 

The Southern Pine Beetle can be one of the most destructive insect pests of pines. It is commonly found on the lower Eastern Shore and Southern Maryland, but its populations have been below outbreak level since 1994 thanks to diligence from MDA personnel who monitor and inform landowners, organizations and farmers about this dangerous pest and effective management practices.

 

The pine shoot beetle, an invasive European pest, was first found in Ohio in 1992 eventually spreading to 16 states, from Iowa to West Virginia and Maine, throughout most of the mid-Atlantic and Northeast areas. The small black beetle lives and feeds in the shoots of pine trees in summer, and burrows into the bark in fall and winter months. In spring, the adult beetles emerge and lay their eggs in stressed or dying pines, recently cut pine stumps, logs and even bark mulch. Damage can occur not only during the changing seasons but also during two phases of the beetles life cycle. Shoot feeding from young beetles during summer results in dead pine shoots and can reduce growth and weaken trees. In the spring, during the breeding phase, adult beetles can kill weak or diseased trees. Infested pines sustain damage to growing shoots and buds, stunting the trees' growth permanently and diminishing its canopy and leaf output. In large numbers, pine shoot beetle adults and even juveniles can weaken and kill otherwise healthy individual trees and even whole stands of pine trees.

 

While Pine shoot beetles are capable of infesting almost all species of pine occurring in Maryland, they will generally not infest spruce and fir trees, instead preferring Scots pine amongst others. Although pine shoot beetles have the potential to be serious forest pests, most damage has been reported from Christmas tree farms where the beetles can reproduce and spread rapidly.

 

Maryland and the MDA is especially concerned about the beetles reaching small Christmas tree farmers who might not be aware of the threat or effective management practices.

 

"Even though we haven't seen much damage in Maryland, we're … on the front lines, trying to keep it from moving into the big, pine-producing regions in the South, including the Eastern Shore," said Carol Holko, manager of the Maryland state Agriculture Department's Plant Protection and Weed Management Section. A Pine Shoot Beetle Quarantine Zone has been put into effect in Baltimore, Carroll, Harford, Howard, Garrett, Alegany, Washington, Fredrick and Montgomery counties in order to help slow the pests advance toward valuable Loblolly pine stands and Christmas Tree Farms on the Eastern Shore.

 

If left unchecked these pests, along with others like the Emerald ash borer and the Asian long-horned beetle, can do massive amounts of damage to not only forested ecosystems but also stands of trees being grown for economic purposes. By monitoring, surveying and educating about these pests we can keep their populations below infestation levels and keep our trees and forests a bit healthier and more productive.

 

Harrison Jackson is the Coastal Stewards Coordinator for the Maryland Coastal Bays Program. 


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