Recognizing Diseases that Harm Your Forsythias
Forsythias are remarkably robust plants and are immune to most diseases. However, while there are one or two insects that attack forsythias, even a healthy plant can become infected. Here are some tips for recognizing diseases and preventing instects from infesting you forsythias.
The trunk and stems of forsythia can be attacked by a fungus if they are injured. The fungus creates a nodule or gall that looks very rough. Prevention of the disease is to keep the fungus away from healthy plants. Check any plants you buy for damage to the bark or for any unexplained swellings on the woody parts.
If you find galls and there are only a few, you can cut-off the infected stem and destroy it. If there seem to be galls on most of the stems the plant must be torn out and destroyed. The fungal spores can attach themselves to your gardening tools so boil and bleach any tools you have used on infected stems. If some of the plant is left growing, recover all the leaves as they fall at the end of the year and destroy them and the mulch under the plant.
Though not very common, this fungal disease attacks the flowers and the stems. The fungus has black fruiting bodies that can develop virtually anywhere on the plant. First indication of a problem is that the flowers start to wither and die. Some stems also show signs of distress before dying. Often this fungus only gets a foothold because the forsythias are in an area of static air and the spores are able to settle and get established. The disease can be halted by cutting out all the dead and infected parts of the plants. To improve ventilation some of the surrounding foliage has to be removed. The older stems on the forsythia should be removed to get rid of any danger of re-infection.
Leaf spots are caused by different fungal infections that are once again enabled by poor ventilation of the plant. With a healthy breeze, most fungal diseases do not affect forsythia because it is quite resistant. Signs of leaf spot are, as the name suggests, spots on the leaves. The spots can look really alarming with colors from yellow to black. If they come together, the spots will resemble some form of blight.
Sometimes the damage to the leaves can be confused with insects because the leaves can be partially devoured. Once the ventilation is improved around the plant, removal of infected twigs and leaves will often be enough to enable the plant to make a full recovery. To make sure all of the infection is removed the pruning should be quite savage. The plant will probably recover after being heavily pruned but another attack of leaf spot will probably kill it. A general fungicide will probably kill off any remaining spores or low level infections.