2024 Tree Pest News

By Jeff Osborne, Forest Stewardship Program Associate 

With warmer weather, it’s not just humans that get more active. There are many pests that could be affecting forests in the next few months. Some are established statewide and have cyclical population spikes and lows; others are newer and spreading across the state. Here’s an overview of pests that are expected to make a large impact and/or spread further within Pennsylvania this year, and what can be done or is happening to address them.

              As in years’ past, this May state agencies are coordinating the spraying of hundreds of thousands of acres of public forests with biological (e.g., BtK) and chemical (e.g., Mimic®) agents from aircraft in an effort to reduce defoliation due to the spongy moth. With the early warm-up, caterpillars may begin to hatch before May 1. Exact spray timing is determined by larva development and oak leaf size. Spray blocks are mostly through the north central and south central parts of the state, with some blocks in Pike and adjacent counties. The treatment areas were identified during egg mass surveys conducted in 2023. Guides to surveying for egg masses, conducting aerial spraying on public land, and interactive maps of PA DCNR and PGC spray programs are available on DCNR’s website. Spongy moth in the forest is most detrimental to oak stands. They can also defoliate fruit and nut trees and shrubs. The USDA Forest Service has a great guide which lists 36 tree species or species groups and whether they are susceptible, resistant, or immune to spongy moth defoliation. It also lists treatment options for small and larger properties.

The map above shows this year’s predicted period when 90% of spongy moths will have hatched across PA. https://bioforest.ca/en/united-states/

Beech leaf disease (BLD) is a newer disease in Pennsylvania. It was first found in Lake County, Ohio, in 2012. As of December 2023, it has been found in every Pennsylvanian county.  

Map showing spread of BLD from its initial discovery in Ohio to its spread into 15 other states and a Canadian province. https://www.clevelandmetroparks.com/parks/education/education-resources/publications

BLD affects all beech species. BLD is associated with the presence of a non-native species of nematode which lives in the buds during winter then feeds on the foliage. It is unclear if the nematode causes all the damage or if it is vectoring a yet-to-be-identified organism that causes further damage. Dark bars between the leaf veins are evident as the leaves develop in early spring. These leaves will either die or their efficiency will be reduced. The disease can spread quickly and cause mortality in saplings within two years after infection. As the disease spreads in larger trees, there will be progressive twig dieback.

            Early-stage beech leaf disease symptom. Photo: Jim Chatfield, OSU Extension

Although no practical forest stand-level treatment has been developed, on a small scale there is research indicating potassium fertilizers help the tree mitigate the effects of the symptoms. There is also the option for stem injections containing the fungicide thiabendazole, or foliar sprays containing fluopyram.

Hemlock has been affected by two non-native invasive species: hemlock woolly adelgid and hemlock elongate scale. As of 2023, the adelgid has been found in every county and the scale is mostly found in the central to eastern part of Pennsylvania. The hemlock woolly adelgid can prove fatal to hemlock trees, but can be treated with insecticide soil drenches which can protect the trees for multiple years. A video that shares the basics of managing the pest can be found here. The hemlock elongate scale can affect spruce and fir species as well. They are similar to native scale insects and may require a specialist to identify them.

For recent information on these pests and others you can view this year’s Forest Health Insect and Disease Briefing  or the USDA Forest Service forest health publication page.