SEASON UPDATES FROM UVM PLANT DIAGNOSTIC CLINIC 7/30/25
Spring was cool and wet, much like last year. As a result, we saw a fair amount of peach leaf curl, caused by the fungus Taphrina deformans. This pathogen causes thickened, purple pink twisted foliage in peaches. It is a bit striking due to the color but really does not cause much harm to the tree, so I do not recommend fungicides, especially in home garden/landscape situations. Here is more info on the disease with pictures and management. https://hort.extension.wisc.edu/articles/peach-leaf-curl/.
Another common issue in wet cool springs is damage from the pear leaf blister mite. This small eriophyid mite causes leaf damage in pear that starts as 1/8-1/4-inchpale green to reddish blistered areas on the leaves. With time, the blisters turn black/brown and are often mistaken for a fungal leaf spot disease. I have noticed in my own pears that the first leaves that emerge have this but the later leaves (when it is warmer) are free of the damage. For garden/landscape situations no treatment is necessary. https://hortsense.cahnrs.wsu.edu/fact-sheet/pear-pearleaf-blister-mite/.
Another common disease in wet cool springs is anthracnose. The fungal pathogen can cause blighted leaves in birch, maple, ash, oaks and sycamore among others. The brown/black dead areas on the leaves often are concentrated around the leaf veins since it stays wetter there longer. In severe cases defoliation may occur and in sycamores there can be a twig blight associated with the disease. If the trees defoliate early in the season they often flush a new set of leaves. By the time you see the disease it is too late to do anything about it and fungicides are rarely warranted. If you have a tree with anthracnose, try to reduce further stress by adequate watering throughout the growing season. Fertilizer is not necessary unless the soil test indicates the need and rake and destroy fallen leaves in the autumn. Prune the tree to remove weak or dying twigs and improve air circulation and light penetration. https://extension.umn.edu/plant-diseases/anthracnose-trees-and-shrubs.
Brown rot of stone fruits was common again this year because we had a lot of rain during bloom. This fungus disease blights blossoms and causes cankers on the twigs resulting in dieback that looks like fire blight except it is on a cherry, peach, plum or ornamental stone fruit rather than an apple host. There is often a droplet of ooze associated with the twig cankers. It can look quite devastating. The fruit that develops often will be covered by the gray/brown spores of the pathogen. Blighted twigs can be pruned out as soon as possible. Any infected fruits should be picked and destroyed. See https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/insects-pests-and-problems/diseases/fruit-spots/brown-rot-of-stone-fruits for pictures of the disease, the lifecycle and management options.
The rainy weather early in the season also sets up susceptible trees to repeated leaf infections of apple scab (https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/insects-pests-and-problems/diseases/scabs/apple-scab),cedar apple rust and Marssonina leaf blight (https://extension.psu.edu/apple-disease-marssonina-blotch) in Malus spp. The past several years crabs and apples have shown early defoliation from these fungal diseases. In orchards this is managed by spraying every week to ten days with fungicides but in a landscape the diseases can be minimized by thorough yearly pruning to open up the tree so leaves dry more readily and by raking and destroying the leaves in the fall. If raking is not an option, repeated mowing of the fallen leaves will also help the leaves breakdown quicker and lessen the number of overwintering spores of the apple scab and Marssonina. Choosing resistant cultivars to scab and cedar apple rust will help avoid the diseases. Cedar apple rust needs two hosts (apple and juniper) to complete its lifecycle, so eliminating one of hosts would eliminate the disease. However, the spores can travel long distances from either plant so you maybe out of luck in a neighborhood! For pictures of the brown woody galls with bright orange appendages on juniper and the yellow leaf spots on the apple host go to https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/insects-pests-and-problems/diseases/rusts/cedar-apple-rust. Cedar-hawthorn rust, in addition to affecting apples and crabapples, sometimes infects pears, quince, hawthorn and serviceberry. Cedar-quince rust has the broadest host range and can infect many genera in the rose family. In addition to those plants already mentioned, mountain-ash, flowering quince, cotoneaster, chokeberry, and photinia are also hosts for this disease.
Rhizosphaera needlecast in spruce continues to defoliate resulting in dead branches in spruces and other susceptible hosts from the ground up as a result of our rainy cool springs.This disease is easily diagnosed by looking at older infected needles with a hand lens. Diagnostic black fruiting bodies in lines emerge from the stomates on the undersides of the needle. Young trees may benefit from fungicide sprays but in older trees the cost is prohibitive. Being sure there is good spacing among trees is also helpful. https://extension.umn.edu/plant-diseases/rhizosphaera-needle-cast.
We are probably in for a repeat of 2024 with more lilac defoliation due to the fungal blight caused by the pathogen Pseudocercospora. Look for brown leaf spotting on the foliage, sometimes coalescing to blight the entire leaf followed by defoliation. Last year many thought their lilacs had died but healthy buds were already set for next year. If you scrape the bark with your fingernail, as long as you still see green,the plant should be fine next spring. However, several years of defoliation in a row may affect the vigor of the plant. Prune the plant thoroughly to open it up to air and light. The bushier the lilac the more disease you will see! Fungicides are rarely warranted but could be used on specimen plants early in the season, but at this point it is too late.
Powdery mildew is also commonly seen this time of year on lilacs and peonies. This pathogen prefers high humidity rather than rainy weather and signs of the disease include the whitish powdery-looking growth on the leaves. Pruning plants and spacing them well helps to minimize this disease.
Spotted Lantern Fly has not been spotted in Vermont yet. Be on the lookout! It is a beautiful little plant hopper that is very colorful. Nymphs are black with white spots and turn red before transitioning into adults. The black nymphs can appear as early as April and until July. Red nymphs are found from July until September. Adults begin to appear in July and are approximately 1inch long and ½ inch wide at rest, with forewings that are grayish with black spots. The lower portions of their hind wings are red with black spots and the upper portions are dark with a white stripe. In the fall, adults lay 1inch-long egg masses on nearly anything from tree trunks and rocks to vehicles and firewood. They are smooth and brownish gray with a shiny, waxy coating (not to be confused with spongy moth formerly known as gypsy moth) when first laid. Adults and nymphs use their sucking mouth parts to feed on the sap of more than 70 plant species, stressing plants and making them more vulnerable to other disease and insect pests. They feed in large masses and excrete lots of “honeydew” which encourages black sooty mold. https://www.vtinvasives.org/invasive/spotted-lanternfly. You can report a sighting here: https://vtinvasives.org/reporting-spotted-lanternfly.
Beech leaf disease continues to spread in the state. The disease is caused by a nematode (microscopic worm). All beech trees are susceptible to attack, and symptoms are easiest to see in the early spring as the leaves emerge.Leaves show a distinct yellow and green banding between the leaf veins and the leaves are often curled and distorted. Dieback in branches occurs each year and eventually the tree will succumb. See pictures and more info here: https://vtinvasives.org/invasive/beech-leaf-disease.
A good resource for disease and pest info is the Landscape Message from UMASS Extension Landscape, Nursery and Urban Forest . The online newsletter provides updates on disease and insect pests occurring on trees and shrubs in Massachusetts. https://www.umass.edu/agriculture-food-environment/landscape/landscape-message.
There is a helpful online map of the latest locations of our statewide invasive forestry pests (beech leaf disease, elm zigzag sawfly, hemlock wooly adelgid, emerald ash borer and elongate hemlock scale). The map is constantly updated. https://experience.arcgis.com/experience/4a3efe4febd24254947e600372793632/page/Statewide-Status/.
If you are seeing a disease or pest problem and need help identifying it samples can be dropped off or mailed to the UVM Plant Diagnostic Clinic, Jeffords Hall, 63 Carrigan Drive, Burlington, VT 05405. Sending pictures is a good place to start. Reach out to Ann at: ann.hazelrigg@uvm.edu.