Sterilize your pruning shears before cutting the plants, and plant clean stock in soilless media to avoid the viruses that are transmitted by nematodes in the soil. Quickly remove infected plants and their parts. In some cases, plant parasitic nematodes can transmit the viruses. Transmission can occur by knives, leaf contact, and insects like aphids. Viral Diseasesįifteen different viruses afflict hydrangeas! Hydrangea macrophylla is the most susceptible. If you have a susceptible plant, you can protect it with copper hydroxide (Kocide). These spots become larger lesions and can kill the leaves. The spots darken and become angular in shape. The first symptoms are water-soaked spots. Photo (cropped) by Elizabeth Bush, Virginia Polytechnic Institute and State University, via via CC 3.0. The bacteria that cause this disease can enter the plant through natural openings like stomata or through wounds.īacterial Leaf Spot (Xanthomonas campestris) on oak leaf hydrangea. Bacterial Leaf Spot ( Xanthomonas campestris) There are no chemical options to control this disease. However, more severe infestations can cause both wilting and root rot.īacterial wilt occurs mainly in hot weather and heavy rains. This important bacterial disease first manifests as blight in the leaves and flower clusters. Bacterial Diseases Bacterial Wilt ( Ralstonia solanacearum) If you know that rust is likely to be a problem, you can grow the cultivar ‘Frosty,’ which is resistant to this disease. Thin inside the hydrangea making sure to disinfect your pruning shears. This disease is difficult to control, but you can manage it by cleaning up infected leaves and debris that has fallen to the ground around both hosts. The first symptoms are orange pustules on the bottoms of the hydrangea leaves and yellow spots on top. arborescens, and hemlock as its alternate host. This rust only infects the smooth hydrangea, H. Like other rusts, hydrangea rust needs two hosts to survive and does not kill either of them. One way to control this disease is to apply a fungicide as soon as you discover it. You can prevent the disease by reducing humidity and increasing air circulation. Powdery mildew is most likely to be a problem on hydrangeas when the days are warm and the nights cool. Left unchecked, the fungus can infect the newly developing buds and stunt their growth. As the lesions get larger, the leaves can turn yellow and fall off the plant.Ī severe case of powdery mildew. Leaf Spots ( Cercospora species and Phyllosticta hydrangea)Ĭercospora manifests as circular purple or brown spots on the bottom of the plant. Options include iprodione, or thiophanate-methyl. If you have a persistent problem, you may need to use fungicides. Clean up debris around the plant, so that Botrytis can’t live on the dead tissue. Treat your pruning shears with bleach as you prune, so you don’t accidentally spread any disease.Īlso remove dead or damaged flowers and leaves to prevent the fungus from gaining egress into the plant. Space them properly, and prune branches that are closely spaced. If you can, keep good airflow around your plants. Don’t water late in the day, and only water at the roots, so you don’t get the flowers and leaves wet. You can take steps to try and prevent this infection. The reddish lesions on the leaves are a sure sign of Botrytis Blight.īotrytis is more likely to be a problem under cool and damp conditions, such as several days of cloudy, humid, and rainy weather.
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