The bottle brush buckeye plant (Aesculus parviflora) is a showy, deciduous shrub so named for its large stalks of white flowers that resemble small bottle brushes. The flower clusters can be upright or drooping, depending on the cultivar. This hardy, woody shrub tolerates common buckeye diseases better than other species of Aesculus family, according to the University of Connecticut. Still, these diseases do affect the bottle brush buckeye, even if they aren't life-threatening.
All buckeyes are susceptible to verticillium wilt, according to North Dakota State University. While this disease can and does kill many other trees and woody shrubs, it usually only kills a few branches of buckeye bottle brush shrubs, if that. This fungal disease lives in the soil and attacks the wood of the shrub. The primary symptom is the leaves of the buckeye turning pale and dropping off the branches. This usually happens from the ground up. Affected branches should be pruned off. Because the bottle brush buckeye is so hardy, this may be enough to save the shrub. Unfortunately, this fungus can live in the soil for years, even if the soil is drenched with a fungicide, so the only way to control for it is to transplant the bottle brush plant to a location with healthier soil.
Powdery mildew is a fungal disease and appears as a white or gray fine coating that covers the broad leaves of the bottle brush plant. There are two types of fungi that commonly cause this disease in buckeyes, according to North Dakota State University. The fungi are transported on water such as wind-blown rain, or if the shrub is watered from above--a practice that should be avoided.
As the water sits on the leaves, the fungus takes hold of the plant. Early leaf drop, yellowed leaves and withered flower buds are all symptoms of this disease, in addition to the powdery coating on the plant. Leave plenty of room around your plant for air to circulate, and water in the morning, when the sun can quickly dry the leaves of the plant. This is not a life-threatening disease, but it can prevent the shrub from blooming and the fungus is unattractive. If the problem persists each year, spray your bottle brush buckeye with a preventative fungicide treatment in the spring. Apply according to the instructions on the label for the size of your plant.
Leaf blotch is another fungal disease that spreads on water. The first symptom is small, brown spots with yellow halos. The spots quickly grow and merge into each other. Sometimes, the leaves will drop prematurely from the shrub. Premature leaf drop may also occur.
This disease is not life-threatening and only affects the appearance of the plant. The fungus can overwinter in the soil, however, so affected leaves should not be allowed to sit on the soil after they fall from the shrub. Instead, gather them up and dispose of them. This simple step may prevent the fungus from returning the following spring, according to North Dakota State University.