Pests and Diseases Ride the Summer Wave

As the weather warms up the time is ripe for pests and diseases to emerge and continue their life cycle, causing damage to our beloved plants.  Now is a good time to keep your eyes open for certain pests so that you can try to get ahead of them and their destruction.  Here are a few pests and diseases you should look out for. 


This moth overwinters in a ‘bag’ cocoon made from silk and tiny chewed up needles/leaves, the eggs hatch in May/early June.  The bagworm is a pest of arborvitae, juniper, pine, spruce, and many other evergreen species.  It also attacks certain deciduous trees such as black locust, honey locust, and sycamore.  Bagworm larvae injure plants when they feed on needles and leaves, leaving small holes in the foliage. Damage by mature larvae is especially destructive to evergreen plants.  When the infestation is light the bags can be manually removed and destroyed, killing anywhere from 300 – 1000 overwintering eggs.  When the infestation is beyond integrated pest management levels you can combat the infestation with JMS oil or Lepitect. 

Bagworms on a Juniper branch

Bagworms on a Juniper branch

Oak Wilt

Oak wilt is a disease that effects oak trees.  It is caused by a fungus, Bretziella fagacearim that develops in the xylem.  All oaks are affected by the fungus, but the red oak group often die much faster than the white oak group.  The oak wilt fungus blocks the flow of water and nutrients from the roots to the crown, causing the leaves to fall off, usually killing the tree.  Red oak group (scarlet, pin, black, etc. ) can die within a few weeks to six months and the disease spreads quickly from tree to tree because the roots of this group graft together, allowing the disease to spread quickly. Trenching between trees is one way to prevent the spread of the disease. White oak group (bur, swamp white, etc) often take years to die, if they die at all, and the disease rarely spreads to additional trees. 

Red Oak Symptoms

-          Brown coloration develops on leaves starting at the outer edge and progressing inward toward the mid-vein of the leaf.

-          Branch dieback may be visible starting at the top of the tree’s canopy and progressing downward.

-          Leaves suddenly wilt in the spring and summer and may fall while there is still some green on them.  Fungal spore mats may develop under the bark of infected trees and beetles who feed on the sap can spread the fungus to other trees.   


White Oak Symptoms

-          Symptoms may develop in the upper crowns of white oaks as with red oaks, but they do not spread as quickly.

-          Sporulating fungal mats are not produced on the living tissue of white oaks and they can recover or take many years to die, which significantly reduces the spread of the disease.

-          Symptoms are often restricted to one or a few branches at a time. Leaf discoloration occurs, but the changes are often more gradual than with the red oak group. 


The best practice is to prune Oaks from October to February. If Oak Wilt symptoms are spotted contact the Department of Environmental Conservation.

Top L to R: grafted red oak roots, red oak leaves affected by oak wilt, comparison image, fungal mat beneath red oak bark

Bottom L to R: oak wilt damage, oak wilt preventative injections to reduce tree loss

Spotted Lantern Fly

The spotted lantern fly is a plant hopper native to China and Southeastern Asia.  It was first spotted in Pennsylvania in 2014.  It presents a threat to both woody and non-woody hosts.  The greatest agricultural concern applies to grapes, hops, apples, blueberries and stone fruit.  Although eradication efforts are underway in Pennsylvania it has been found in Delaware, Maryland, New Jersey, New York and Virginia.  Spotted Lantern Fly eggs are laid on any hard, smooth surface, including plants, trucks, stones and bricks.  Nymphs are able to feed on many hosts, but adults prefer Ailanthus altissima and grape vine.


The plant hopper pierces the plant and sucks up sap.  Piercing the plant’s tissues and feeding on the sap weakens the plant, causing it to weep, giving off a fermenting odor and leaving a dark colored trail on the bark.  They also excrete honeydew while feeding, which may encourage the growth of sooty mold if the infestation is high. 

Think you’ve spotted the spotted lantern fly in New York?  Check out this website for more information.


spotted-lanternfly stages.jpg

Emerald Ash Borer

This invasive beetle from Asia infects and kills North American Ash species.  The adult beetles leave distinctive D-shaped exit holes in the outer bark of the branches and the trunk.  The adults may be present from late May – early September, but are most common in June and July.  Signs of infection in the canopy are dieback, yellowing, and browning of leaves.  Increased woodpecker activity is often the first sign of EAB infestation.  This increased pecking can lead to “blonding”, large strips of bark falling off.  When the trees bark splits or falls off, s-shaped larval galleries may be visible.  Most trees die within 2-4 years.  EAB is not a particularly strong flier, therefore most long distance movement of EAB has been directly traced to ash firewood or ash nursery stock.  New York State currently has a regulation restricting the movement of firewood to protect our forests from invasive pests.  Ash is a very common street tree in many New York communities, so keep an eye out for these signs.

Top L to R: larvae in an S-shaped gallery, emerald ash borer (actual size .5”), EAB emerging from D-shaped holes, blonding area is covered in S-shaped galleries

Bottom L to R: notice of pesticide application on Union St. in Brooklyn, injection sites, an alley of EAB casualties

Aaron Smith