The creativeness of a creative woman
I think the most frustrating thing about gardening are the pesky bugs and diseases. There is nothing worse than to spend time and effort on your plants/flowers only to have them munched on by tiny critters or come down with an illness. Our best defense is to recognize the symptoms and take corrective action before the plant is overcome and stressed to the point of dying.
The diseases listed below are not specific to only Hydrangeas, some can also affect other flowers, shrubs, trees, fruits and vegetables. If available I have provided a link to a fact sheet (in pdf format) from a University or State Extension Office for the specific disease. They include more detailed information and pictures.
Petals turn brown and fall. Leaf spots form, especially where faded petals have fallen. Flower buds are killed before opening
Remove and discard attached and/or fallen leaves. Space plants to insure good air circulation. Maintain low humidity. Avoid watering late in the day. Remove and discard leaf debris. Apply chlorothalonil, iprodione, mancozeb, or vinclozolin.
CERCOSPORA LEAF SPOT
Tan spots with reddish-brown halos develop on leaves.
Rust spots occur with too much direct sunlight after overhead watering.
Remove and discard attached and/or fallen leaves. Water at the base of the plant, in a manner that keeps moisture off the leaves. Protect foliage with mancozeb, copper, or chlorothalonil.
Yellow areas form on leaves. These may become purplish. White, cottony fungal growth forms on the lower surface of the leaf.
Erysiphe polygoniOccurs in shady locations when the hydrangea gets poor air circulation. Space plants so there is good air movement between them.
Management:Remove and discard any leaves (attached or fallen) with traces of mildew or fungus. Apply a few ounces of skim milk in a quart of warm water sprayed on just the affected area or apply triadimefon, piperalin, thiophanate methyl or fenarimol to protect leaves.
The abnormal development of green pigmentation on plant parts not normally green. Flowers may be stunted. Leafy shoots grow from the flower parts. Plants decline and die.
Discard infected plants. Maintain good insect control.
Leaves may be mottled, have yellow spotting, dead flecks, line or ringspot (pale colored rings) patterns. Plants may be distorted or have flower color breaking, or few flowers.
Hydrangea Ring Spot virus, Tomato Spotted Wilt virus , Hydrangea Latent virus
There is no cure for viruses in plants. The infection is systemic, so all tissues in the plant carry the virus(es). Remove plant and as many of the roots as possible – they are also infected. It is suggested to wait a year before replanting another hydrangea in the same site. Residual roots take some time to deteriorate, and contact between old and new plant roots can cause virus transmission to the new plant. Viruses can be transmitted in plant sap. Gardening tools will be infective once coming into contact with the diseased plant. Therefore, be sure to disinfect gardening tools before the next visit to the garden patch.
Photo shows Hydrangea Ring Spot virus
Hydrangeas are minimally affected by most pests with the exception of deer which savor the young, tender green buds and foliage much as we might a salad. Wire cages or fences are the most effective defense. Deer can devastate unprotected plants in a day or two. Slug and snail damage can also be a problem as they chew extensively on new foliage. There are organic baits that are very effective and will not harm children, pets or other wildlife. Aphids, thrips and spittlebugs are attracted to soft new growth on some plants but do minor damage. All three of these insects may be washed off with a strong jet of water or sprayed with a solution of 1 quart of lukewarm water and 1/3 teaspoon of liquid castile soap.
I hope this has given you some insight as to some of the problems you might run across with Hydrangeas. There is a tremendous amount of ongoing research in regards to the diseases listed above and from what I have learned cultivators are striving to produce plants tolerable to them.
Next stop on my Hydrangea posts? – Pruning and General Maintenance.