The UNH Cooperative Extension Office in Brentwood is receiving calls from seacoast residents regarding leaves falling from their white ash and oak trees.
The leaf diseases causing these problems are called Ash Rust and Anthracnose. This is the second year in a row in which these diseases have infected seacoast area trees. The recent spate of rainy weather creates ideal conditions for these diseases to proliferate.
Ash Rust is caused by the rust fungus Ruccinia sparganioides. Symptoms show up in mid-May as small yellow to yellow-orange spots on upper leaf surfaces. About ten days later, bright orange-yellow pustules become apparent on leaf under surfaces. Leaves become wilted and fall off the tree. Ash rust has a secondary host, marsh or cord grass. This disease is especially prevalent in ash trees adjacent to salt marshes or creeks.
Anthracnose is caused by several pathogens and infects ash, oak, maple, sycamore, and dogwood trees. Leaves exhibit a scorched or blighted appearance, wilt and then fall off. With the exception of sycamore and dogwood trees, where the blight will also affect twigs and stems, the disease is not usually fatal to ash, oak and maple trees.
Once the symptoms appear, it is too late to apply a fungicide. The best control method is to rake up any infected leaves and twigs that fall from the tree, and dispose of them by bagging them, burning them (a permit may be needed from your town fire officials), or by taking them to your transfer station for disposal. You should not compost infected leaves, as the source of the pathogen will remain on your property.
If you have a specimen tree you would like to protect next year, a fungicide can be applied by a licensed arborist just as the leaf buds are breaking.
If you have any questions, contact your local UNH Cooperative Extension Office or the UNH Cooperative Extension Home and Family Garden Center at 1-877-398-4769.
UNH Cooperative Extension provides New Hampshire citizens with research-based education and information, enhancing their ability to make informed decisions that strengthen youth, families and communities, sustain natural resources, and improve the economy.