Maple trees are extremely popular in home landscapes all over Georgia. Some maple species are native to this part of the country, so they naturally do well with limited maintenance.
You can find several varieties that do well in our area, including red maple, sugar maple, silver maple, paperbark maple and Japanese maple.
We have experienced large amounts of rainfall in the past few weeks, and with it, perfect conditions for fungal leaf spot.
Most leaf spots require high temperatures, high humidity and extended periods of leaf wetness to infect their host. Of course, this season the weather conditions are optimal for fungal diseases.
There are two leaf spots known to affect maple trees. The first is called Phyllosticta, or purple eye. This is caused by the fungus Phyllosticta.
These fungal spots can be round or irregular, and are about a quarter inch in diameter.
They have purple margins with yellow or tan centers.
A small black fruiting body will appear in the middle of the diseased area, somewhat resembling an eye. The good news is that Phyllosticta leaf spots are mainly an aesthetic issue and rarely cause any long term damage to maples.
Phyllosticta leaf spot is the most common disease I see of the leaves of Japanese maples, especially on the darker varieties, such as "Bloodgood."
The disease appears as small, round bleached spots, easily contrasting the dark red of the leaves.
Another common leaf spot on maples is tar spot, which is caused by the fungus Rhytisma acernium.
We normally see this disease in spring and early summer.
Tar spot first appears as light-green or yellow round areas. These spots then develop a black, shiny, tar-like dot on the upper side of the leaves. In many cases, leaves with several spots will prematurely drop to the ground. This is another example of a leaf spot is more of an aesthetic problem.
Your best defense against these fungal leaf spots will be proper management.
Rake all of the leaves from around the maples in the fall and remove them from the property. The fungal spores survive the winter on the fallen leaves, so this will help remove much of the disease pressure.
However, I always see weedy red maples growing on roadsides, so the disease spores will always be present.
Pruning may also help control these diseases by allowing more air flow to dry out the leaves. If your affected maples have a very dense canopy with many touching branches, you may consider pruning out several of the branches.
Be careful to avoid too much pruning in the summer months, as this will stress the root systems and leave the pruning wounds open to fungal infection.
Chemical control is rarely needed, and is most often not feasible due to the size of most maple trees.
However, some homeowners choose to treat their Japanese maples because they are small enough to easily spray and are expensive enough to justify the cost. Propiconazole, a systemic fungicide, can be found in the brand names "Bonide Infuse" and "Fertilome Liquid Systemic."
Chlorothalonil, a contact fungicide, can also be used against Phyllosticta leaf spot. It can be found under the brand name "Daconil," which is the product name used by several different companies.
Always read and follow all label directions when applying pesticides.